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Comment by redis_mlc | Hacker News Reader

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Why bother to disinfect when you can ventilate? Air with pathogens out, fresh air without pathogens in.

(Regarding herd immunity: you're aware that at the current rate of 55000 people per day, it would take 10 years to infect 60% of 320 million people? Nothing to say of the countless casualties that you would get in the process.)

Since eradicating the virus has become impossible, most national governments are currently pursuing a herd immunity strategy by default. They're just doing it at slightly different rates.

In the USA the current daily rate of confirmed new cases is about 43000, not 55000. However there are a large number of "dark matter" cases not counted in official statistics. About 40% of infections are asymptomatic, and many more are paucisymptomatic. Most of those patients never get tested.

Agree with "herd immunity strategy by default". Absent a vaccine, about the same percentage of people will become sick, while a larger percentage is exposed but does not become sick. At some point, again minus a vaccine, few enough people will be left as potential replicating hosts, that the virus will not be replicating fast enough to maintain the country's epidemic. Countries will differ by the breadth of the curve, but not the area under it (adjusted per-capita of course). On the other hand, if you are one of the countries with a long curve, and an effective vaccine arrives before the end of it, you benefit.

What countries are actually following a strategy to reach herd immunity by having "enough" people fall ill and hopefully recover (having "recovered" does not preclude persisting damages btw!)?

Most countries are rather waiting for a vaccine to become available and try to minimize the number of sick and dead in the meantime without interfering with economy too much.

(54.4k was number of newly confirmed cases on friday 10/2 by the John-Hopkins University btw. I'm aware that the US has inadequate testing [0] and that the real number is going to be a lot higher than this.

[0] https://ourworldindata.org/coronavirus-testing#the-positive-... )

A vaccine is unlikely to wipe out the virus for good. They just aren't that effective. We can't wipe out other coronaviruses or the common cold by vaccination even if we wanted to.

It will continue to circulate in the population, just in a less explosive manner. This also means it is possible we will never reach herd immunity in some absolute sense much like we haven't for other coronaviruses.

Only New Zealand, Taiwan, Vietnam, and maybe a couple other countries are actively avoiding herd immunity. Regardless of their public statements, other countries aren't actually trying to minimize the number of sick and dead. The public health measures in place are generally insufficient to contain the pandemic, so I predict that many areas will reach a significant level of herd immunity before a safe and effective vaccine is widely available. We won't know whether that prediction is accurate until about a year from now.

Probably cheaper to slot a component into your HVAC than it is to re-engineer it to draw outside hot air, cool it, and still keep interiors at a comfortable level. (Reverse for winter)

My house has a fantastic filter along with a UV system as well. When I bought the house I thought it was overkill, but now I’m quite happy it’s there.

The amount of heat in the air is small compared to that in other materials; buildings with stone or concrete walls have a sufficient heat capacity that you can ventilate without temperature changing too much. This works less well for buildings with wooden walls though.

Ventilating properly requires discipline though. No tilted/semi-opened windows for prolonged time for example. In winter, heating should be turned off and the windows should be as wide open as possible to minimize the time to exchange air. That's to reduce the loss of heat. 5-10 minutes of ventilating is good enough, usually. We usually don't have air condition here, so I don't know what's the recommended process in the summer.

It's common to ventilate like this in Germany in the winter for example. I know (now returned) former German expats that completely missed this development. They still tilt windows and let the heating run all day long.

US buildings are designed to recirculate most air for energy cost reasons. Ventilation sounds like a good idea, but it doesn't match how things work today because of how stale the air becomes.

(That's why in Silicon Valley large companies have "air consultants" measure the freshness twice per year and report the rate. I've talked to some.)

So my question stands on how and what to do to have more effective air circulation indoors, and what else we should do. And why is this conversation only happening several months into a lockdown. It's as if American government is falling down from learned helplessness.

I was thinking HEPA filtration may already cater for virus's, but with HEPA certification being .3 microns and the COVID-19 virus 0.12 microns, then it gets down to individual air conditioning systems. Some may use ionising in combination or UV.

So I foresee a whole raft of legislation and requirements for office spaces ahead. Which will only help drive the work from home long-term as cheaper office space. But also help shift us away from open plan offices that I've never met anybody who liked.

As for herd immunity - that really is best effective against viruses that do not mutate that quickly. Corona-viruses from my understanding, do mutate. Though it is often the case that mutations of a virus over time lean towards mutations that make them less impacting upon the host. Which may be down to natural selection in that those with no impact can spread it more and no virus really wants to kill the host. Impacted/dead hosts tend to be less effective in transmission. So may very well be down to that aspect in why they tend to become less impacting.

On the UV aspect https://www.nature.com/articles/s41598-020-67211-2 a UV wavelength of 222nm that is effective against the virus and safe for humans. Though how stable current UV output is and by that if you had a 222nm light, over time would that drift and become less human safe is something I'd want to check.

There again - flu's and colds are more prevalent during winter months when we have less sun and less UV. Can't ignore that pattern.

> but with HEPA certification being .3 microns and the COVID-19 virus 0.12 micron

HEPA can filter sub-0.3-micron particles, and the effectiveness trends to be even higher than its performance at 0.3 microns.

Although it's not certificated, but it's often true from a practical standpoint, due to the physics of mechanical filtration in general. The reason of using 0.3-micron in certification, is because it's the point where HEPA filters are the least effective. 0.3 um is the most difficult size to filter. Effectiveness goes up at both ends.

The effectiveness of HEPA filters trend to follow a U-shaped curve [0]. Below 0.3 um, particles are captured by the diffusion mechanism. Above 0.3 um, particles are captured by the interception and impaction mechanism. Around 0.3 um, neither mechanism is effective, and efficiency reaches a minimum.

[0] https://en.wikipedia.org/wiki/File:Filteration_Collection_Me...

Here's a document from a HEPA filter maker explaining the four mechanisms involved in a little more detail [1].

[1] http://donaldsonaerospace-defense.com/library/files/document...

> Corona-viruses from my understanding, do mutate.

Already, reinfection by different strains of COVID-19 has been documented (by DNA sequencing) in Korea. The more people who catch COVID-19, the greater the space of possible genetic mutations can be explored. Some of those mutations may decrease severity, but others are likely to merely increase the presympomatic contagiousness period.

All viruses mutate, but so far SARS-CoV-2 has been mutating relatively slowly. It has an error correction mechanism which blocks the majority of mutations. By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year.

The human species already has a significant level of herd immunity against four other endemic coronaviruses. The same thing will eventually happen with SARS-CoV-2 one way or another, but hopefully we will have an effective vaccine soon enough to accelerate that process while minimizing the death toll.

> By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year.

That's true, but that might change soon (the "every year", not the mutation speed): Results of [0] are supposed to be published this quarter. I am hopeful for them to be positive.

[0] https://www.biondvax.com/2020/07/last-of-12400-participants-...

There are plenty of viable ways to disinfect closed spaces, like cold plasma generation [0] or UV light disinfection [1].

[0]: https://drexel.edu/now/archive/2020/April/cold-plasma-filter...

[1]: https://www.cnet.com/health/can-uv-light-protect-you-from-co...

Thankfully you missed that the article discusses history from 1956 regarding the airborne transmission study methodology. Otherwise you might have gotten a heart attack. Goodness!

And remember all that "all scientists say masks dont work, why are you wearing a face mask, are you stupid?" only to change to the exact opposite in may/june ?

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