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Comment by timr | Hacker News Reader

> This should not come as a surprise, and it was largely predictable from the outset....the flu has a base reproduction number (R0) less than 2....Covid has an R0 in the vicinity of 2.5....In the meantime, public health measures like masking and distancing will work against both viruses....there's really no need for conspiracy theorizing.

Assuming that this is due to "masking and distancing" and the small difference in R0 is crude thinking. It's unlikely to be anything of the sort.

First, R0 is not a fixed constant. It varies by context and location, and we've seen influenza decline everywhere.

Second, R0 is an estimated value. There are big error bars on all of these estimates -- the overlap is far greater than the 0.5 you're using to claim causality.

Third, rhinovirus has not gone away (estimated R0 < 2). Nor has adenovirus (estimated R0 ~2.3) [1,2]

There's something far more interesting going on here, it is surprising, and it isn't a "conspiracy theory" to talk about it. It's science.

(FWIW, my current favored hypothesis is that the closure of schools, and possibly travel, significantly affected the spread of flu. Unlike Covid, kids are a significant vector of spread for influenza. It's one of those little facts about Covid that is...politically incorrect...to acknowledge right now. But I am speculating, and there are problems with this theory as well.)

[1] https://syndromictrends.com/metric/panel/rp/percent_positivi...

[2] https://www.medrxiv.org/content/10.1101/2020.02.04.20020404v...

View on HN

> and the small difference in R0 is crude thinking.

Given the reproduction number appears as the base of an exponent, I would not consider the difference "small."

If influenza has a typical R0 of about 2, reducing contacts by 50% would make its growth non-exponential. If covid has a typical R0 of about 2.5, doing the same would require a further 20% reduction of contacts, to 40% of baseline rather than 50%. Since population behaviour and legal restrictions have diminishing returns (eliminating casual contacts first at lower cost, then progressively higher-cost and more essential contacts), this could easily correspond to a large difference in effected (necessary) policy.

> Second, R0 is an estimated value. There are big error bars on all of these estimates -- the overlap is far greater than the 0.5 you're using to claim causality.

I have seen no credible evidence that typical (non-pandemic) influenza has an R0 greater than that of SARS-CoV-2. If you have a citation handy to the contrary, I'd be interested in seeing it. In the meantime, I tried to be generous in my estimation of influenza's R0; even your reference [2] places its central estimate at 1.68.

> Third, rhinovirus has not gone away (estimated R0 < 2). Nor has adenovirus (estimated R0 ~2.3) [1,2]

Rhinovirus and adenovirus both have mean-estimate R0 greater than that of influenza in your reference [2], so if policy is going to eliminate any of these disease from general circulation then influenza would be the first.

Furthermore, some analysis does show limited evidence of a reduction of rhinovirus cases (https://www.nature.com/articles/d41586-020-03519-3). A confounding factor here, however, is that we don't really have comprehensive like-against-like monitoring for rhinovirus in the way developed nations monitor for influenza. Adenoviruses as a broad category are also not limited to respiratory transmission, so air-focused restrictions would have less effect on these other routes.

Finally, I reiterate that flu has a pronounced seasonal variation, whereas rhinovirus is somewhat less variable. A set of social responses only needs to prevent the flu season from starting to make it "disappear."

> Given the reproduction number appears as the base of an exponent, I would not consider the difference "small."

The difference in measurement is small, relative to the error in measurement.

Look at the error bars on the R0 estimates in that paper. Influenza runs from 1.06 to 3.4. You are trying to make micrometer inferences from a parameter where our best estimates are measured in libraries of congress.

I'm not a clinician or public health policymaker, so I'm operating on the balance of probabilities rather than a p=0.05 standard.

If you consider the influenza estimate independent of equivalent estimates for covid, then there's a substantially greater than 50% chance that influenza's R0 is meaningfully smaller than that of the flu. If the estimates are partially dependent (i.e. methodology that gives a larger estimate for influenza would also give a larger estimate for covid), then that chance goes up further.

Moreover, we also have evidence in the actual observations of epidemic dynamics. Over the southern hemisphere fall of 2020 (northern hemisphere spring), covid cases increased more rapidly than influenza cases in countries that were entering their flu seasons. That's compelling-to-me evidence that covid in fact has a larger basic reproductive number, whether that be due to a fundamental difference in the virus or just the effects of low baseline immunity.

Now, your idea that the particular set of policy restrictions may be more effective against influenza than covid is very interesting. There's a basic horse sense to it, as well, since policymakers were largely operating from a playbook written for a flu pandemic. However, I do not think that "more effective" is a necessary component of the argument; "at least as effective" will do just as well given influenza's low baseline prevalence (out of season).

Remember, my original point upthread was not to explain every bit of the relative epidemic curves, but instead to claim that we really ought not be surprised by the difference. I see little need to resort to specialized theories to explain the broad outline, even though I'm sure they will be helpful in the details.

Your 2nd paragraph seems to have a mistake: influenza vs flu?

> we also have evidence in the actual observations of epidemic dynamics. Over the southern hemisphere fall of 2020 (northern hemisphere spring), covid cases increased more rapidly than influenza cases in countries that were entering their flu seasons. That's compelling-to-me evidence that covid in fact has a larger basic reproductive number

Yes, we know that SARS-CoV2 increased, and influenza went away. That's trivially observed. We don't know why flu went away.

To turn that observation around and say "Covid grew faster than flu, and therefore it has a higher R0, and therefore, the flu went away because {insert your favorite NPI} was just good enough to stop it" is begging the question.

It could just as easily be any number of other factors that you're not accounting for. There's also a number of other faulty assumptions inherent in your logic. For starters: there's no particular reason, a priori, that a person couldn't have both flu and SARS-CoV2 in the same year.

+1 for the first constructive, correct use of the phrase "begging the question" I have encountered this year.

You are dodging parent's point:

> I have seen no credible evidence that typical (non-pandemic) influenza has an R0 greater than that of SARS-CoV-2. If you have a citation handy to the contrary, I'd be interested in seeing it.

Even if the difference in R of influenza and SARS-Cov-2 was only 0.1 (and there is no evidence suggesting the average difference is that small) and assuming both pathogens spread in a similar fashion [1], then over time SARS-Cov-2 will fluctuate around the meta-stable point of 1.0 and as a result influenza will decrease exponentially.

[1] https://virologyj.biomedcentral.com/articles/10.1186/1743-42...

I am not dodging it. As the parent noted in their own post, the best mean estimates we have for SARS-CoV2 are a fraction of a unit away from the best mean estimates we have for influenza or rhinovirus.

Trying to use this tiny relative difference in fuzzy estimates of empirical parameters to make a complex causal arguments about...well, anything...is folly.

Sorry to be harsh here, but that's exactly what I meant by dodging: Parent asked for evidence that the R0 of influenza is higher on average than the R0 of SARS-Cov-2.

If there are no studies to show, refer to an opinion of an epidemiologist or any other expert in the spread of infectious diseases.

You seem to argue against a vast field of computer scientists, mathematicians, physicists, biologists, medical experts that do nothing else but study the spread of infectious diseases.

> Sorry to be harsh here, but that's exactly what I meant by dodging: Parent asked for evidence that the R0 of influenza is higher on average than the R0 of SARS-Cov-2.

Burden is on the parent to prove their claim, not for me to disprove claims advanced without evidence.

All current estimates for R0 have wide, overlapping confidence intervals that make it impossible to differentiate them from other viruses. The best anyone can say is that Covid and influenza have similar mean R0 estimates.

> If there are no studies to show, refer to an opinion of an epidemiologist or any other expert in the spread of infectious diseases.

I cited just such a paper. Please refer to it.

> Burden is on the parent to prove their claim, not for me to disprove claims advanced without evidence.

Multiple people have cited many papers that all generally agree with the trend that influenza has a lower r0. You've discounted those by making what are ultimately statistically unsound claims.

> I cited just such a paper. Please refer to it

The paper you cited supports the other person's contention: that r0 of influenza is lower than that of covid.

> The paper you cited supports the other person's contention: that r0 of influenza is lower than that of covid.

As "the other person[1]," I'd like to point out for the sake of accuracy that the paper you mention here does not in fact study covid. While published in February 2020, the "SARS-CoV" it talks about was SARS 1, not the virus behind the current pandemic.

I've taken my prior for covid's R0 from sources such as the CDC (https://www.cdc.gov/coronavirus/2019-ncov/hcp/planning-scena...), which seem to report a best guess of about 2.5 with some room for variation.

[1] -- Who is also leaving the argument. We've both made our points well enough for others to form their opinion, and I don't think there's much unexplored territory.

Last spring COVID was managing to achieve rapid spread at the same time that the flu season naturally ended. Despite the challenges in measuring R0 for both, this is pretty direct evidence that R0 is higher for COVID than for the flu.

R0 is not static. As people become immune to the current strains and the virus mutates, people will still have partial immunity to the new strains. Some people will be fully immune depending on their antibody response and the mutations.

Next year it is entirely possible that the R0 of covid drops below influenza.

If you introduced influenza to a naive population (i.e. native americans) you would get massive death.

<<Experts believe that as much as 90 percent of the American Indian population may have died from illnesses introduced to America by Europeans>>

R0 is indeed static. It's R(t), the reproduction rate at time t, that is not static.

how does that work? Native Americans didn't have disease Europeans where not exposed to? Only Europeans had diseases?

any info about this? very interesting

Europeans did bring back disease they weren't immune to:

Europeans brought deadly viruses and bacteria, such as smallpox, measles, urope. Europeans brought deadly viruses and bacteria, such as smallpox, measles, typhus, and cholera, for which Native Americans had no immunity (Denevan, 1976). yphus, and cholera, for which Native Americans had no immunity (Denevan, 1976). On their return home, European sailors brought syphilis to Europe. Although less n their return home, European sailors brought syphilis to Europe. Although less deadly, the disease was known to have caused great social disruption throughout eadly, the disease was known to have caused great social disruption throughout the Old World (Sherman, 2007)

https://www.kellogg.northwestern.edu/faculty/qian/resources/... (Note that I haven't read this whole thing, but wanted to find a source for my little factoid)

It is one of the major points from Guns, Germs and Steel. Most of our major diseases have transferred from domestic animals. For example both measles and smallpox (the two most deadly diseases for Native Americans) come from cows.

Europeans successfully domesticated animals, Native Americans did not. So Europeans had diseases that Native Americans were not adapted to.

I believe the theory is that Europeans kept various domesticated animals and Native Americans had far fewer, and that those animals were frequently sources of new diseases. Europe was also more interconnected, so diseases may have spread farther while Native diseases died out.

See the wiki page: https://en.m.wikipedia.org/wiki/Native_American_disease_and_...

ohh that makes sense, thanks

Small but important correction: nothing can make epidemiological spread non-exponential. Driving base reproduction below one additional infection per infected patient means the exponent is less than one, so the incidence of the disease rapidly decreases. This decrease is also exponential by definition: infection is simply an exponential process, and an exponential equation doesn't stop being what it is when the exponent is less than one.

The steady state is exactly 1, which is like balancing a pencil on its point.

It's plausible that two things happened here: the various local restrictions reduced the R0 of flu below 1, and the border closures kept mutations from traveling: and influenza is notoriously mutation-prone.

These can combine to practically extirpate influenza. Unfortunately, the effect is temporary, and the next flu season is likely to be a real doozy.

Which will be "fun" because our societies now have a hyperactive immune system, and there will be considerable political pressure to "do something" about the next flu wave. This must be resisted but I'm not optimistic.

> The steady state is exactly 1, which is like balancing a pencil on its point.

At exactly one, it's indeterminate; you could see a subexponential growth or decay. With no exponential terms remaining, lower-order terms that are ordinarily hidden by exponential growth become the dominant observables. (Since epidemic spread is also random, you're much more likely to see the stochastic terms show up in the overall statistics in these cases. You really can be lucky or unlucky with Rt ~= 1, but there's no persistent luck with Rt >> 1.)

This is also important before community spreading sets in, and it is the mechanism by which contact tracing can work. Rather than change the general susceptibility of the population to the disease (changing the effective reproduction number), contact tracing tries to operate at the level of individual cases in ways that cannot be scaled to uncontrolled community spreading (even if Rt is close to 1).

> and the border closures kept mutations from traveling: and influenza is notoriously mutation-prone.

Perhaps, but are influenza mutations an important effect within a single flu season? I know the determination of to-be-dominant strains has a great effect on the composition of each season's flu vaccine, but as far as I am aware we don't see declining flu vaccine efficacy over a season.

By the way, now that we are already talking about R ~= 1 ...

Over pretty much the last year you could observe, in different countries all around the world, that the reproduction number was 'magically' floating around 1.

Only recently did I learn that this effect was puzzling for epidemiologists as well and was only solved around 2012 (?) in a model that assumes a network of information about the disease in parallel to the network of disease transmission. The resulting feedback loops lead to the meta-stability of R=1. Super interesting how society acts as this distributed information processor, similar to 'the market' in economics.

A well-known Norwegian economic commentator pointed this out in a newspaper article a few weeks ago. You'll eventually be forced to maintain an R~=1 no matter what you do, so it's best for everyone if your cases have a low baseline when that happens. The measures will be the same, but the baseline risk can either be terrible or okay.

You can almost see the phenomenon in real time during this pandemic. Countries that have low trust in authorities will still freak out when the epidemic hits biblical proportions, and do various forms of impromptu distancing measures which will bring the R number down. Then when the signs of panic subside, they'll loosen them. And so on.

Societies with high trust in authorities will still pressure their authorities to loosen up when things feel safe, with predictible results, leading to further lockdowns.

The economic deviation caused by governments over reacting is your biggest pressure. Unless you shut down all travel, bars, restaurants, schools, universities and dating.

Then all of this will come back in the future and kick you in the teeth. Either we're going to have to accept this as a way of life, which is more detrimental. Or we're pushing off the inevitable.

No one has overreacted, unless you accept an outcome that both leads to improvised individual social distancing and the even worse worse economic devastation that follows.

This was uncertain to most people last year, but now we’ve seen so many examples that it really shouldn’t be so controversial any longer. But if it wasn’t, we wouldn’t be discussing it.

The covid virus is evolved to fit exactly into the niche of societal behavior where it will be a big fucking problem but not so bad that it’s immediately obvious to enough people.

We're not talking about a single flu season, effectively we're talking about skipping an entire flu season.

Influenza is pretty promiscuous. In normal conditions, very few people aren't exposed to it: either their existing immune resistance (vaccinated or otherwise) is up to the job, or it isn't.

Mutation is therefore the primary driver of flu, year upon year. This is why vaccines are continually reformulated for a best-guess at what strains are going to be dominant.

We had just concluded a northern-hemisphere flu season when travel restrictions started to kick in. This was followed by at least a 90% reduction in international travel, and for most of what remained, it was mandated that new arrivals isolate for long enough to eliminate any influenza they might have carried.

Lockdowns would mean less mutation to begin with, since it happens in human hosts. And such mutations as did present are going to have a tough time jumping oceans, and even when they do arrive, spreading through the populace is substantially inhibited.

Ironically, the universal mask mandates are likely to be more effective against flu than against COVID. Like it or not, masking has minimal effect on spreading aerosols, although using a "real" mask, and being pretty careful to wear it right, can mitigate inhaling those aerosols.

Influenza is believed to be spreadable through aerosols, but the primary vector is droplets, while the opposite appears to be true for SARS2. Bog-standard cloth masks are fairly good at keeping droplets off people and surfaces.

People don't inhale 1 or 0 covid particles they inhale n particles where reducing the value of n makes transmission less likely. Keeping more of your spit to yourself reduces chance of transmission even if masks are imperfect.

> Like it or not, masking has minimal effect on spreading aerosols

[citation needed]

> The overwhelming majority of transmission of SARS-CoV-2 is via large respiratory droplets as conclusively demonstrated by contact tracing studies, cluster investigations, the lack of infection spread in hospital settings with universal masking protocols and the low estimated R.

https://www.pennmedicine.org/updates/blogs/penn-physician-bl...

> The principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory droplets carrying infectious virus.

https://www.cdc.gov/coronavirus/2019-ncov/science/science-br...

From what I can tell, you may have your flu/covid mixed up. Covid is spread through respiratory droplets, the spread of which is reduced by wearing a mask.

Both those sources may be out of date now (July and October). While there is limited experimental evidence for airborne transmission except in animals, there is even less evidence for fomite & respiratory droplet transmission.

The claim that "lack of infection spread in hospital settings" rules out airborne transmission due to masking is also questionable. The opposite seems true. As I understand it, infections in hospital settings have been routinely documented throughout the pandemic despite masking, contact protocols, etc. - which implicates airborne rather than droplet/fomite transmission.

This is a really good article in the Lancet recently which solidified my opinion on this. It offers 10 items of evidence for airborne transmission being the primary driver of the pandemic.

https://www.thelancet.com/journals/lancet/article/PIIS0140-6...

For me, the key points are:

> Second, long-range transmission of SARS-CoV-2 between people in adjacent rooms but never in each other's presence has been documented in quarantine hotels.7

> Sixth, viable SARS-CoV-2 has been detected in the air. In laboratory experiments, SARS-CoV-2 stayed infectious in the air for up to 3 h with a half-life of 1·1 h.12 Viable SARS-CoV-2 was identified in air samples from rooms occupied by COVID-19 patients in the absence of aerosol-generating health-care procedures13 and in air samples from an infected person's car.14 Although other studies have failed to capture viable SARS-CoV-2 in air samples, this is to be expected. Sampling of airborne virus is technically challenging for several reasons, including limited effectiveness of some sampling methods for collecting fine particles, viral dehydration during collection, viral damage due to impact forces (leading to loss of viability), reaerosolisation of virus during collection, and viral retention in the sampling equipment.3 Measles and tuberculosis, two primarily airborne diseases, have never been cultivated from room air.15

> Seventh, SARS-CoV-2 has been identified in air filters and building ducts in hospitals with COVID-19 patients; such locations could be reached only by aerosols.16

> Eighth, studies involving infected caged animals that were connected to separately caged uninfected animals via an air duct have shown transmission of SARS-CoV-2 that can be adequately explained only by aerosols.17

> Tenth, there is limited evidence to support other dominant routes of transmission—ie, respiratory droplet or fomite.9, 24 Ease of infection between people in close proximity to each other has been cited as proof of respiratory droplet transmission of SARS-CoV-2. However, close-proximity transmission in most cases along with distant infection for a few when sharing air is more likely to be explained by dilution of exhaled aerosols with distance from an infected person.9 The flawed assumption that transmission through close proximity implies large respiratory droplets or fomites was historically used for decades to deny the airborne transmission of tuberculosis and measles.

>> there will be considerable political pressure to "do something" about the next flu wave. This must be resisted

Why on earth does it make sense to resist sensible public health measures to reduce the influenza to R0<1?

The measures would not need to be nearly as drastic as those for COVID ("normal" R0 of 2 vs 2.5+), so more handwashing (good to minimize a broad spectrum of pathogens), masks (already culturally ordinary in many countries), and especially better indoor ventilation systems would be a long-term benefit to everyone.

I'm mostly hoping that the success of better sequencing, mRNA vaccine technology, and the rapid development deployed for CV-19 will also be applicable to influenza and help minimize or practically eliminate it.

Are you assuming other measures?

"so more handwashing (good to minimize a broad spectrum of pathogens), masks (already culturally ordinary in many countries), and especially better indoor ventilation systems"

Let's not forget a substantial portion of the population working from home, using less public transportation (choosing to travel by car when traveling at all), a huge decrease in tourism and large public gatherings, much less eating out at restaurants, contactless food delivery becoming the norm, etc.

So many factors figure in to why much of the (wealthy, developed) world is a lot more resistant to contagious pathogens today than it was a year ago.

Politicians have shown themselves throughout this pandemic to be opportunistic authoritarians who obviously don't believe in their mandates since they break them themselves so frequently. There's no reason to expect that these sociopaths won't jump at the opportunity to drink more from the fountain of power again given the chance. Since they've gotten away with so much this time, they might even be tempted to go even further next time.

Are you serious?

If anything, politicians have vastly under-managed the situation, timidly afraid of offending constituents' offense at any inconvenience, and only partially at best following sound science.

In states that did issue orders for masks and stay-at-home, the orders were weak, late, and lifted early, resulting in multiple waves that only abate now because of the rapid deployment of vaccines.

Most importantly, there was very little and late funding to cover the costs of those who should most have been shut down, group travel, entertainment, dining, etc. - should have been fully shut down immediately, and everyone's costs covered.

6-10 weeks of hard shutdown, while standing up a full masking, test/trace/isolate protocol would have handled it, yet few countries did it.

A few countries did implement early, strong, and effective measures, such as New Zealand. They also then opened up many months earlier than the rest of the world with near-normal life.

Where are the politicians "drunk with power" who are restarting lockdowns for their own gratification?

Where is the advantage for such a "drunk on power" politician? What could they possible gain by unnecessarily implementing measures that are seen at best by the smart ones who understand it as a necessary inconvenience, and by the rest as an assault on them?

Even flat-out authoritarians do no such thing. E.g., China, who is unashamed to run literal concentration camps for Uyghur minorities, and who did hard lockdowns at the start, is not opening up as soon as scientifically feasible.

Unless you can show some citations of evidence, this looks a lot less like a real phenomenon, and more like a pseudo-libertarian teenager's trope.

This is basically a fantasy. Public health measures that restrict freedom are unpopular even when they are justified. More than anything else your least favorite lawmaker wants to remain employed and to do so they will eventually bow to the will of the people even when the people are ignorant.

Public health measures that you disdain aren't popular where they are because your neighbors want to step on your neck they are popular because people who know more than you do know they on net save lives.

When there is nothing to be gained by such measure support will blow away like dust in the wind. There is no battle for you to fight.

Those measures are not entirely different from the measures previously suggested, though.

Obviously your quoted poster’s concerns are less about “hand washing”, “wear a mask if you have symptoms”, and “stay home” while you recover, and instead are about an overreaction in which entire businesses are forced to shut down, children without symptoms are forced to wear masks even as they run and play, and people are forcibly prevented from leaving their homes “just because it’s flu season”.

This may be necessary, at times, for COVID-19, but as you recognized, not for the normal flu.

Given the spotty record of both public and private policy with regards to using actual science as a driver, these are not invalid concerns.

Or put differently, rather than presuming that anyone against “doing something” is against “common sense” measures, perhaps we should be supportive of making sure that we do something, AND that the “something” that we do remain in the realm of common sense, to assuage the very real concerns that “doing something” could mean something more harmful than good.

The normal flu can be pretty bad. In 2018 the spike in total deaths in TX and surrounding states were between a third and a half of the covid spike in those regions. Masks might have been a good idea in 2018 and I hope they become part of our culture at least when you think you might be coming down with something. You know, that first day of a cold when you are telling yourself its allergies or drainage. Shutting down stores makes less sense.

How about a culture and social support system where you can just stay home and rest if you feel something's up? Probably a lot more efficient than a mask, and would probably help with lots of other problems as well.

Plenty of people, hourly, gig, and self-employed people don’t get paid if they don’t work. You might be able to force some of those to be paid while sick-not-working, but the last category will be very difficult to address without either missing a lot of folks or creating tons of fraud and grift risk (and represent a lot of interactions with the public).

I think this goes under culture and social support system. Perhaps worth a thought that giving more support for everybody can help everybody. This interaction is quite apparent in e.g. epidemics, but probably has similar effects for many phenomena.

Of course it falls into the category of social support system, but what the specific design choices are matter in terms of driving behavior.

If I (salaried) take a sick day, I get paid the same amount from the same source; there’s next-to-no economic incentive for me to risk the health of others by working when sick: problem is solved.

We could more or less force the same by law for scheduled hourly workers. It’s a little more difficult for gig. It’s basically impossible (as I see it) to put self-employed people at the same outcome as if they worked without substantial risks of under-comping some and over-comping others.

It seems pretty clear that the person you’re replying to agrees with you, they just committed the crime of stating your position more succinctly.

Washington state has a tax funded state paid sick leave program for anyone who has worked at least n hours in the prior year and paid into it.

But sometimes it is allergies, and you feel fine and want to get some work done. Masks aren't a big deal, I forget I have mine on, and I wear it all day. Maybe some people have more difficulty? If I vwas in construction or something more physical vthan typing I might vfeel differently.

People who are subject to allergies know they are so and allergies doesn't cause most of the same symptoms. You could probably differentiate most cases of sickness by simply taking your temperature.

I think most people have allergies now don't they? It didn't used to be that way. I get colds with no fever usually.

I think only 1 in 6 or 7 are allergic to anything if you mean seasonal allergies to pollen what most people seem to mean when they say they feel poorly from allergies its only half as prevalent.

That is to say most people don't have allergies to confuse with illness and although you might wake up feeling poorly for a number of reasons flu sufferers are liable to suffer from one or more distinguishable symptoms for example for myself when I've contracted the flu I always get a really shitty body ache.

It's possible to get a cold without also having a fever. You are absolutely correct about that but even in that instance the majority are liable to be able to know when they are ill. They just don't stay home because the social pressure has been in favor of bringing your sickness to work as if you were doing everyone a favor by showing up and making your cohorts sick.

When I was a kid with allergies I think it was 15% had allergies. Now 30% of adults and 40% of kids have them. https://www.webmd.com/allergies/allergy-statistics

Sometimes my throat is sore but its just allergy drainage. It doesn't help that the things I'm allergic to line up with flu season.

7.8% of Adults suffer from hay fever. *1 Around 50 million out of around 330 or about 15% suffer from any sort of allergies according to the AAAAI *2 which references data from the CDC

https://www.aaaai.org/about-aaaai/newsroom/allergy-statistic...

https://acaai.org/news/facts-statistics/allergies

1 Hay fever, or allergic rhinitis, is a common condition with symptoms similar to those of a cold. There may be sneezing, congestion, runny nose, and sinus pressure. It is caused by an allergic response to airborne substances, such as pollen.

2 The American Academy of Allergy, Asthma & Immunology (AAAAI) is the most prominent membership organization of more than 7,000 allergists / immunologists (in the United States, Canada and 72 other countries) and patients' trusted resource for allergies, asthma and immune deficiency disorders. This membership includes allergist / immunologists, other medical specialists, allied health and related healthcare professionals—all with a special interest in the research and treatment of allergic and immunologic diseases.

WebMD's doesn't actually seem to actually source their data at all despite styling it like a link for some reason and since their is a disparity between what the CDC and AAAAI say I strongly suspect they are full of shit

I only think I have very occasional allergies by observing my health during the pandemic. I have no clue what it's from. I just assumed they were colds before, though I certainly had less illness of any kind this last year.

"Shutting down stores makes less sense."

Depends on what you want to achieve. If you like a increase of infection, you do it like here in germany and close down hardware stores etc. multiple times on short notice, without telling when they will open again - so people try to storm them before they close, all coming closely together by doing so, which they would not have otherwise.

This particular type of unintended consequence has been repeated multiple times during the crisis, it's puzzling.

For example here in order to avoid contamination in public transports they limited the hours of service. Consequence: same number of people took transport but in less time, increasing density and contact.

Similarly with the curfew forcing shops to close earlier in the day, more people gather in less time.

Most of the measures the public health community is pushing are:

- Paid sick leave. First and foremost.

- Increased flexibility for people WFH as possible if sick or vulnerable.

That's really about it. Maybe masking, though that well has been throughly poisoned.

We will be lucky if we can normalize washing your hands more and staying home when you are sick. The idea that we are going to react to flu with fanatical zeal and need to prepare to resist public health measures is a fantasy promoted by those who are preparing to fight a war that exists only in their own heads.

We've had, in the past year, at various times, public policies that have prevented grocery stores from selling "non-essential" items such as towels and blankets (while allowing alcohol), halted critical health services such as cancer treatments, and led to people from the same household being verbally and physically assaulted for not distancing or wearing masks - after a period of time in which people were verbally chastised for wearing masks when the official stance was not to.

We've sorted a lot of this out over the past year, but there is an all time distrust of institutions surrounding both policymakers and the public health recommendations informing them, and there's a reason for it.

We can either help assuage people's fears (whether you see them as founded or unfounded) by empathizing with their concerns and experiences and addressing them while ensuring that any measures enacted remain rooted in science that we can trust...

OR we can be part of the problem for why there's so much distrust, by ignoring anyone who may have real experiences that have caused them to lose trust in our science and health institutions, and telling them that it's all in their head.

I strongly hope for the former, myself.

OR we can shutdown social media. A lot of the misinformation has been spread through social media - it has a tendency to amplify extremism by providing 'echo chambers' people can select into to reinforce their preconceptions.

> children without symptoms are forced to wear masks even as they run and play

Well, yeah, they can be asymptomatic, spread their sickness to other kids, who then take it home to their parents and grandparents.

Agreed. There seem to be too many folks frantically "doing something" these days. The road to hell is paved with good intentions.

At a super fundamental level, epidemics take place on a social graph. In a well connected graph spread will be exponential, but depending on graph shape it could be something else.

In particular you could imagine that if people never venture outside their own block that the social network is an euclidean graph. In an ideal case where people are evenly spaced in the plane and only interact with neighbors, the disease would spread as a circle expanding outwards, so total infections would be proportional to ~ t^2, and current infections ~ t.

You are essentially describing a supersized plaque assay (https://en.wikipedia.org/wiki/Virus_quantification#Plaque_as...).

I'm perplexed why anyone would downvote this comment; it seems very interesting and insightful to me.

I'm perplexed as well. That the perfect mixing models most people think of for infectious diseases are an imperfect approximation of the actual dynamics on a graph is well known in epidemiology.

>>Small but important correction: nothing can make epidemiological spread non-exponential.

“Exponential with R varying over time” and “not exponential” differ only in interpretation imposed by an observer.

> infection is simply an exponential process

No, in the hyperidealized perfect mixing scenario, its a logistic process, like most other resource constrained processed that look exponential when analyzed over a dhort period.

In the real world, its neither exponential nor even perfectly logistic, even before considering changes to the environment in which the disease spreads (including those induced by the disease, including people’s response to knowledge of it.)

> Which will be "fun" because our societies now have a hyperactive immune system, and there will be considerable political pressure to "do something" about the next flu wave.

So, do something by taking a flu vaccine like is already available and recommended for annual use by the CDC?

The flu vaccine isn't hugely effective at the best of times, and with flu disappearing worldwide and global travel locked down I don't see how they'll even be able to figure out what strains to target for the next one.

Even when not perfectly matched, the flu vaccine does offer some protection.

Both @makomk and @enkid seem to be right [0].

[0] https://www.cochrane.org/CD001269/ARI_vaccines-prevent-influ...

> Unlike Covid, kids are a significant vector of spread for influenza

Kids are significant spreaders of both influenza and Covid (after school reopenings, in many countries kids become one of the top sources of inter-household Covid spread). They just tend to have mild or absent Covid symptoms and didn’t require regular testing for work etc., and therefore did not get consistently tested in most parts of the world. In some places parents deliberately avoided testing their kids for fear positive tests would interfere with their in-person schooling or extracurricular activities.

Repeated claims that kids don’t spread Covid were politically motivated and based largely on junk science.

Admittedly doing good studies was extremely difficult in places like the USA where spread was wildly out of control and contact tracing was completely overwhelmed.

Actually, what you're saying is untrue. The overwhelming evidence shows that children spread COVID less than adults do.

My favorite is this: https://www.nejm.org/doi/pdf/10.1056/NEJMoa2006100?articleTo...

The study isolated SARS-CoV-2 samples from every positive case, sequenced genome of virus, and tracked the mutation patterns. So, that will avoid a lot of the errors that improper qPCR usage can result in.

First things first, age and viral susceptibility:

> Of the 564 children under the age of 10 years in the targeted testing group, 38 (6.7%) tested positive, in contrast to positive test result in 1183 of 8635 persons who were 10 years of age or older (13.7%). In analyses involving participants up to 20 years of age, we observed a gradual increase with older age in the percentage who tested positive (Fig. S5).

That's more about who got it, but there's some discussion of transmission here where the senior author talks about it: https://www.sciencemuseumgroup.org.uk/blog/hunting-down-covi...

> Children under 10 are less likely to get infected than adults and if they get infected, they are less likely to get seriously ill. What is interesting is that even if children do get infected, they are less likely to transmit the disease to others than adults. We have not found a single instance of a child infecting parents.

> There is an amazing diversity in the way in which we react to the virus.

---

(I recognize I only presented one study here - there's only so much time in the day :P - but the other high-quality studies I've seen confirm this. Mechanistically it makes sense if you look at the enormous T-cell cross-reactivity in those age groups. And BTW, data on school closures for Influenza (which children seem to transmit much more readily) showed that school closures were ineffective anyway because they would just spread it more outside of school)

Interesting that this was getting downvoted. Obviously relates to what the poster above was saying about it being "politically incorrect."

We may disagree on what the science implies, but downvoting someone for sharing research means that people are refusing to listen to anything that disagrees with their preconceived notions.

(I guess perhaps the implicit assumption is that anyone pushing articles that show that kids are at less risk, or that kids don't spread Covid as well, must also be pushing for all kids to be running free and socializing?)

Edit: And now this comment is getting downvoted. Folks who disagree, why not speak up about what's wrong with the study, instead of just downvoting?

To be fair, that implicit assumption is pretty strong. There is an absurd bias to push kids back in schools so parents can get back to work.

Still, your points stand that there are some good studies showing kids are not necessarily the major spreaders. It is somewhat surprising to me, but it is data.

I work from home. My wife stays at home and takes care of young kids.

We sent our 6 yo back to (in person) school because computer school was a bad idea.

I have a friend who teaches high school. He is SO relieved to be ending computer teaching.

I think so people want in person school so parents can work, but plenty of people want in person school because it IS better.

I empathize. We had to switch to home schooling because we couldn't keep home internet.

I also think in person is better than remote. I can still think the bias to make it look safe to send kids back to school feels forced.

> but plenty of people want in person school because it IS better.

For some kids, lots of data showing some kids thrived and improved while others suffered.

There is an absurd bias to push kids back in schools so parents can get back to work.

Why is that absurd? Millions of Americans (mostly women) have had to work less or leave their jobs entirely in order to take care of their children, which is a major hit to both their finances and careers. It's a huge cost.

It is somewhat surprising to me

It shouldn't be if the media had been doing their jobs, but due to either incompetence or bias they haven't. People really don't seem to realize that schools have been open in large parts of the US (and many other countries) for months, and it hasn't led to mass infections of students or teachers or parents.

I'm far enough on the liberal end that a living income makes sense to me. Raising your kids is a job. And it is of value to society that one can do that well. Juggling low paying jobs is not beneficial.

Focusing the "child" cutoff at ten seems dubious. Why not set it at an age that includes school extra curricular activities? :(

As a parent of a 6 year old and 8 year old, I'm thankful for this cutoff. Many studies define child as <= 18 or < 20, and I'm not sure how relevant they are for our particular situation.

I'd prefer both. There is a meaningful difference in both compared to the rest of the world.

Similarly, nursing homes and any other assisted living makes sense as a category.

I think it’s entirely reasonable to believe that individual kids are more resistant to spreading COVID, but closing schools is a powerful intervention. Schools have _lots_ of kids in them, in close proximity, and _every_ child lives in a household with at least one, but on average more than one, other person.

This is not the only study implying closing schools was a sensible step:

https://www.nature.com/articles/s41562-020-01009-0

I'm going to lift one part of your quoted material, because this should get more eyeballs:

> We have not found a single instance of a child infecting parents.

That is a really strong claim. It also goes against common logic.

Children are more likely to be asymptomatic. Fine. They tend to resist the virus better, and avoid severe cases even when they do get it. Yup, all good so far. They are less likely to infect others around them. Still makes sense.[ß]

What doesn't make sense is that transmission probabilities in the list are all above zero. From a purely mathematical perspective, transmission probability of "infected child -> parent" should not be zero. I am not stupid enough to dispute scientific finds, but I strongly suspect there are more factors in play.

Also the cynic in me notes that "infected child -> parent" is NOT the same as "infected child -> adult".

ß: Recent news indicates that the latest variants do spread more aggressively among children and teens, and are more likely to show up with symptoms in them. I haven't seen anything about increased mortality among the same groups, though.

Would you mind providing a source for your assertions?

It should be an internet rule that whenever someone calls something scientific or trashing something as poor science, they should provide scientific references. I'm referring to you here.

2 was published in Feb 2020, so not sure how helpful that is...

1 is not normalized data. It does not account for testing frequency. These percentages are of tests using BioFire. My hospital, for example, does not use BioFire to test for SARS-CoV-2 and so we end up running BioFire much, much less frequently than during a normal year.

Anecdotally non-COVID respiratory infections in hospitalized patients have decreased dramatically. Working on trying to demonstrate this with data.

> 2 was published in Feb 2020, so not sure how helpful that is...

It's a meta-analysis of many other papers. The estimates for the other ILIs have not changed significantly in 2020. Again, this is nitpicking that misses the forest for the trees: the differences in estimated R0 between these viruses is not so precise as to be useful for claiming the effectiveness of something like "masks and distancing".

> 1 is not normalized data. It does not account for testing frequency

This is incorrect. The data is normalized across all samples. Your hospital's non-participation may change the coverage of the sample, but that doesn't really matter when it's just showing you that rhinovirus hasn't gone away.

In the paper associated with 1 it says:

The FilmArray RP test utilization rate (TUR) metric is defined as the non-normalized number of RP patient test results generated each week across the Trend sites (computed as a centered 3-week moving average). To calculate the pathogen detection rate (as displayed in Figure 2 [second data view] and on the Trend website), we compute the rate for each organism at each institution as a centered 3-week moving average. To adjust for the capacity differences between sites, a national aggregate is calculated as the unweighted average of individual site rates. Only data from sites contributing more than 30 tests per week is included to avoid noise from small numbers of tests. Because the calculation of pathogen detection rate includes results from patients with multiple detections, the detection rate for all organisms can, in theory, add up to greater than one. In practice, this does not occur.

These are rates. This does not account for testing frequency. If they only tested 1 person in the United States tomorrow, and they had rhino/entero, the graph would show 100% (obviously it wouldn't and they won't only test 1 person). That means that if testing decreased, because for example there were less patients with symptomatic viral infections, but the % positive stayed the same, the chart would not appear to change, even though there were fewer cases...

paper: https://publichealth.jmir.org/2018/3/e59/

The TUR is not the metric plotted on the website. Read the very next sentence in the section you're quoting:

> To calculate the pathogen detection rate (as displayed in Figure 2 [second data view] and on the Trend website), we compute the rate for each organism at each institution as a centered 3-week moving average. To adjust for the capacity differences between sites, a national aggregate is calculated as the unweighted average of individual site rates. Only data from sites contributing more than 30 tests per week is included to avoid noise from small numbers of tests. Because the calculation of pathogen detection rate includes results from patients with multiple detections, the detection rate for all organisms can, in theory, add up to greater than one. In practice, this does not occur.

The TUR is the the raw number of hits across all sites. They normalize this, which is why they talk about it possibly exceeding 1.0. It's why the Y-axis of the plot is labeled in percentages. The height of the bars is a moving average of detection rates across their network.

Regardless, this is still nitpicking. The point was that these other pathogens have not gone away. They have not. Even if you were right, it wouldn't change the argument.

> 2 was published in Feb 2020, so not sure how helpful that is...

When [2] speaks about SARS-CoV, it's referring to the earlier SARS-1, not SARS-2-aka-covid-19.

Possible explanations include:

- More asymptomatic transmission of rhinovirus/enterovirus and adenoviruses than influenza. People often don't notice these illnesses, so wouldn't assume it is COVID and quarantine like they would for influenza.

- More fomite spread than influenza. They may be more stable on surfaces or in food

These are reasonable theories as well. Though the second one would really have to be "SARS-CoV2 has more fomite spread than flu" to explain the observations.

In general though, any sort of explanation that focuses on differences in transmission is more plausible than hand-wavy theories involving R0 and masks. People just desperately want to find evidence that the stuff we did this year made a huge difference.

> People just desperately want to find evidence that the stuff we did this year made a huge difference.

I don't think that's true at all. People have been receptive to the increased evidence that transmission on surfaces is pretty unlikely, for example, despite all the efforts we've put into sanitizing surfaces.

I think most people can appreciate that all the shit we threw at the wall throughout the pandemic eventually comes down to how much effort it is vs how much benefit we get from it. And our understanding of each measure has changed over time. We now know, generally:

Masks indoors are low-effort, medium reward. Masks outdoors are low-effort, low reward.

Cleaning surfaces is medium-effort, low reward.

Staying home is (economically, societally) high-effort, high reward.

To be clear: I'm not making a specific argument about masks vs. sanitizing vs. whatever here.

I'm just saying: responses like the OP immediately leap to the conclusion that influenza went away because of all the stuff we did. It's an error in logic, driven by the emotional desire to believe that the stuff we did must have had a serious impact, and that anything else is not worth serious discussion.

That's ideology, not science.

I agree that leaping to conclusions isn't science. It doesn't get past the hypothesis stage and needs proper study.

That said, if the massive reduction in flu cases isn't a result of some or all of our Covid efforts, it'd be a hell of a coincidence.

> That said, if the massive reduction in flu cases isn't a result of some or all of our Covid efforts, it'd be a hell of a coincidence.

Mmmm...I wouldn't go that far. Like I said, my current preferred theory involves schools, but other plausible theories involve things like mutual inhibition: infection with one virus somehow interferes with infection by the other.

We have some evidence of this happening in the past. Strains of influenza have abruptly vanished due to this phenomena.

Certainly, I'd agree that this is interesting (which is pretty much where I end up on this, vs. the OP, who thinks the matter is settled.)

more generally, it's likely due to greater (indoor) distancing, of which school closures is a subset. the slight differences in transmission characteristics between flu and covid (also represented as differential r0) likely makes flu relatively more susceptible to reduction by distancing.

and distancing is a first-order mitigation that overwhelms the effects of inferior/ineffective mitigations like cleaning, sanitizing, mask-wearing, extra ventilation, etc. those secondary mitigations can make more of a difference when we want to pack it in, like at a movie theater, but otherwise they don't do much because those circumstances are relatively rare.

folks just don't want to accept such a simple answer because it means there's not much to hang their anxiety on, and that cognitive dissonance is unacceptable, as it always is.

> I'm just saying: responses like the OP immediately leap to the conclusion that influenza went away because of all the stuff we did. It's an error in logic, driven by the emotional desire to believe that the stuff we did must have had a serious impact, and that anything else is not worth serious discussion.

I feel like you're coming down too hard on OP. He makes a valid argument.

> immediately leap to the conclusion that influenza went away because of all the stuff we did

It's not an error in logic. It's a reasonable conclusion to draw based on what we've seen and the links he provided. Whether it's true or not, that's debatable and probably nobody here on HN is going to figure that out definitively.

I'm really not sure why you're so argumentative without actually providing any substantial arguments against OP. It feels more like you're the one arguing from an ideological basis.

Having school age kids means constant illness at home. Not usually severe, but annoying.

Was one nice perk having kids at home. 9 months of no illness.

6 weeks after going back family had Covid. No it’s back in the routine of mild illness at least monthly.

For clarity: are you genuinely claiming that you believe school closures prevent influenza transmission but that you think other related mitigation strategies like mask-wearing, restaurant closures, work-from-home, etc... don't?

That seems a little denialist, honestly.

Flu causes fever, which is one of the signs of covid, causing people to isolate. Whereas colds like the rhinovirus have different symptoms and are less likely to cause fever and so they 'fly under the radar' as it were.

> Unlike Covid, kids are a significant vector of spread for influenza.

Children, in fact, have been hypothesized to be the primary reservoir for influenza.

The implication of this is that it would be much better to vaccinate all children against influenza rather than everybody else.

Isn't that already the case worldwide? I live in Russia and all schools are routinely vaccinated every autumn here.

I have never heard of such a thing in the US. Someone else will have to chime in about European countries.

I live in Europe and never experienced such a thing. Perhaps to be more specific: I grew up in Spain and now live in the UK. To the best of my knowledge, children keep catching the flu every year and passing it on to their parents, who instead pass it on to their colleagues in the office (or used to, before 2020).

Romania, Luxembourg - no flu vaccinations from what I see.

> This should not come as a surprise, and it was largely predictable from the outset....the flu has a base reproduction number

I feel like you constructed a straw man by snipping this out from the parent comment:

> work against both viruses. If people become reluctant to socialize because of covid (whether or not there be legal restrictions), they will also not spread the flu.

You can socialize from 6 feet and with a mask. I took the parent to include staying home in their assessment and I have no clue why anyone would think otherwise. It's peak social distancing.

From the CDCs tips for social distancing:

> Choose Safe Social Activities: It is possible to stay socially connected with friends and family who don’t live in your home by calling, using video chat, or staying connected through social media.

Where I live in Canada schools never really closed and we are seeing the same thing.

Most of the Europe didn't close schools either or very short periods when numbers where out of the roof. School closure is American teachers union thing really, vast majority of the countries do whatever possible to send kids to school as it takes the priority above everything.

This makes sense. I've always caught a flu or cold in the tube or in the office, usually from an infected parent. Last year many parents were enjoying a flu-less life while the schools were closed, only to catch it again a week after opening the schools again. I don't have kids, so last year, for the first time in my life, I didn't spend a single day sick.

Which doesn't mean it's necessarily a good thing, as all these bugs will come back with a vengeance against immune systems.

Dueling anecdotes:

I live in a country where schools have stayed open and our 2 kids have been going to daycare normally throughout the whole pandemic.

Our kids have also been eerily free of colds/flus this winter, after the previous winter where it seemed like they had fevers weekly and so much snot they'd choke on it while asleep.

>FWIW, my current favored hypothesis is that the closure of schools, and possibly travel, significantly affected the spread of flu. Unlike Covid, kids are a significant vector of spread for influenza. It's one of those little facts about Covid that is...politically incorrect...to acknowledge right now.

You say "unlike covid". Maybe I'm biased because half of my family was infected with covid by a 6 year old(everyone's fine now) . Also here in Poland all 3 of our covid "waves" came few weeks after kids went back to schools (no masks are required at schools here, because feelings). It is obvious kids at schools are a very significant spread factor second only to spread at the workplace (also no need for masks at the workplace for some stupid reason unless you are public facing).

It is infuriating that tens of thousands of people have to die, because idiot politicians make policy based on stupid factors. For example, it would be inconvenient for everyone at workplaces to have to wear masks so let's tell them to ensure desks are 1.5m apart and everything is fine despite the fact they are not. There was even a local study done recently that estimated 40% of all covid cases were infected at the workplace. This info was major news for few days, then nothing changed and everyone forgot about it.

Also, the pinnacle of stupid (bordering on malice - hopefully it will be prosecuted eventually) is making covid treatment policy based on expected drug availability not on what works. It has been proved recently(9th of April) in Lancet corticosteroids given early on lower the incidence of hospitalisation a lot. However, despite many letters from the public "official medical guidelines" in PL still say the exact opposite using an irrelevant study as justification.

* The study is irrelevant because they measured efficacy of those steroids on people that are already hospitalised,it found no impact on death rate of already intubated people. The study authors also extrapolated their research of hospitalised intubated people to people pre-hospitalisation and for some reason wrote in their abstract corticosteroids given early actually have detrimental effect (no proof of this assumption in their study whatsoever).

Then the second study comes out that measures efficacy of (inhaled) corticosteroids in real early covid patients.It finds it significantly lowers development of symptoms that require hospitalisation. Everyone ignores it. Meanwhile we have over 80 thousand "extra" deaths in a country one tenth the size of US.

Oh, and my claim is that people making decisions on covid policy are perfectly aware of their wrongdoing because transcripts of their meetings are mysteriously unavailable.

My feeling is people are told to stay home when sick with flu like symptoms, this would also specifically target flu.

A R0 of 2 vs 2.5 is enormous. The OP's post was correct.

Did we even test for the flu? Or did we just presume that flu cases were COIVD because the symptoms are so similar?

The idea that the flu just 'disappeared' despite world trade continuing just sets off my bullshit detectors. Between all the countries that did little or nothing initially, and the people who refused to wear masks and didn't lock down...there's just no way it dropped to zero. Less? Sure. But gone? I simply don't believe it.

Yes, everyone with ILI symptoms (influenza-like-illness) who goes to one of the clinics or hospitals participating in the surveillance program gets tested for about 30 pathogens. That's how we know what's going on with all those critters.

None of that has changed in the era of COVID, although the pattern of who goes to clinic for what may have. If there were flu out there we'd be detecting it is the bottom line.

Around Autumn it was subtly mentioned that the UK figures were going to be for flu and covid combined.

Before that it was noted that flu was killing more than coronavirus in summer.

Do you have any links to substantiate those claims, please?

You have to understand - it was REAL subtle.

You have to understand: your claims are nonsense without evidence.

The WHO has the FluNET program and they constantly test a fixed set of people with respiratory symptoms for flu, all around the world.

FluNET is precisely why we know flu dropped so much, and hence the large chunk of people with respiratory symptoms have been COVID-19 or otherwise, but certainly not flu.

Thanks for sharing. That's why I was asking.

Also, username-bro.

Yes. They didn't just stop testing for flu when someone shows up with influenza-like illness (i.e. flu, covid). Maybe in some places where medical systems were already struggling in normal times, but not in developed nations certainly.

Most flu patients don’t get tested for flu.

Indeed, most flu patients don’t even see a doctor.

So, at the outset, the flu stats are coming from a very specific category of patients: in-patients and people with great insurance who have the time and money to get tested for the flu (even though it won’t make a bit of difference what the test says as it’ll be over in a couple weeks anyway.)

This second-category may be skewing things.

The personality-type that has a ‘need’ to know whether they have the flu was instead focused on Covid. They’d have the sniffles, go through a drive-through Covid testing site, get their negative result and breathe a sigh of relief. They would NOT however make an appointment with their doctor as they perhaps would have in years past as (a) they wanted to avoid sources of Covid, and (b) the doctors were discouraging appointments but for emergencies (and flu-like symptoms plus a negative Covid test, would not, in the patient’s mind, amount to an emergency.)

I doubt this explains all of the decrease in flu-positive tests. But, perhaps some of it.

It didn't drop to zero. "Gone" is hyperbole - it was an extremely light flu season, but it wasn't zero or anything like that.

And yes, we test for influenza a lot.

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