WHO study on Covid-19: We estimated that the median of estimated R0 is 5.7 | Hacker News Reader

WHO study on Covid-19: We estimated that the median of estimated R0 is 5.7

wwwnc.cdc.gov

81 pointspaganel23 comments

If R0 is truly 5.7 - roughly 82.46% of the population must become immune before “herd immunity” kicks in.

((R0 − 1)/R0) is known as the “herd immunity threshold” — that is, with an R0 value of 5.7 the computation would be ((5.7 - 1)/5.7) or 82.46%

Learn more here, — “Herd Immunity”: A Rough Guide: https://academic.oup.com/cid/article/52/7/911/299077#3862683

As a comparison, here are the R0 values of other well-known infectious diseases: https://en.m.wikipedia.org/wiki/Basic_reproduction_number

I read this recently:

I've noticed a fair number of people assuming the herd immunity threshold, 1 - 1/R0, is the total proportion of the population infected. It isn't; it's the proportion of the population immune (i.e. has had the disease; in this model that's assumed to confer immunity) at which the epidemic stops growing. The total proportion of the population infected is called the epidemic final size (I'll call it 'F'), and is given by

F = 1 - e-R0*F

This is higher. Lots higher. For R0 = 2, it's 80%. For R0 = 3.4 (the WHO estimate), it's 96%.

Appreciate the information, though citing notable sources might help others understand and add credibility too.

For example, “Herd immunity & epidemic final size” covers the topic:

http://alizon.ouvaton.org/Report2_Immunization.html

Obviously that can't quite be universally right, look at Brazil, look at Malaysia, India. Look at Easter Europe. It is pretty clear it can't be 5.7 all across the board.

I fear Brazil isn't really testing much.

Anecdotal data: A relative in Brazil got tested three weeks ago and the results still have not come back. (~100k from sao paulo).

They said it would take 10 working days to have the results.

So I wouldn't trust any Brazilian numbers.

(she was diagnosed with pneumonia, but she luckily recovered. in the household everybody else also got sick, and also eventually luckily recovered)

Ro is the spread without mitigating factors, so Ro is more or less assumed constant.

That said, there's no reason to think the particular places you're naming are either doing effective testing or mitigating factors. People tossing around the statistics of a given country without looking deeply at the testing process have been confusing the situation for a while here.

Moreover, a lot of these quotes wind-up wrong as they're stated. "Look at Eastern Europe". I can see fast exponential in Romania, maybe other parts of the area are still in "don't ask, don't tell" but doesn't prove anything.

R0 changes from location-to-location and from culture to culture.

Case in point: the Flu is affected by temperature. Its R0 is lower in the summer (when the Flu dies) and higher in the winter, aka Flu season.

COVID19 does not seem to be affected by the heat, but its almost certainly affected by population density. The R0 of COVID19 will be higher in cities (ie: Wuhan China or New York City), and lower in rural areas.

But its good to see estimates for R0. We need a number to base our decisions upon, to get a rough gauge of how bad this virus could get. Whether or not all of these measures we're doing matters, or if its worth the tradeoff of harming the economy.

we will see, but it is just hard to fathom that with all these social distancing measures in place you still have 400K in the US and seemingly very few in Brazil and all these other places where for large swaths of the population social distancing is not an option.

It might be that the R0 is far more variable than assumed.

> social distancing measures in place

R0 is the measurement of what will happen WITHOUT social distancing.

In effect, researchers calculate R0 to determine if social distancing / lockdowns / etc. etc. would be worthwhile.

------

The virus's real reproductive rate is called "R" (which is obviously lower now, due to social distancing / masks / etc. etc.). R0 is the "if we did nothing" variable.

What's the correct way to say 'R0 with social distancing?'

That is to say, R0 in a hypothetical place that was always practicing social distancing?

Because as I understand it, R0 is used to calculate herd immunity, but a lot of people are curious about what the herd immunity numbers would look like if we continued to take measures such as 6ft/2m distancing and wearing masks (efficacy debated, I know) and face shields.

Or those places aren't testing? The UK has ~62,000 confirmed cases and ~7,100 deaths - that implies a > 10% mortality rate which is definitely not true. Why is the mortality rate so high? Because they only test those with severe symptoms - the actual number of cases is much higher than 62,000.

To be fair, the mortality rate could be a lot higher than estimated. That has huge error bars too. We all look on the bright side (why it might be lower). There's also a dark side.

Based on what? Nothing points to a higher mortality rate - but some countries are admittedly not testing a lot. Even if you quadruple the estimated mortality rate, the UK numbers would still be under-represented.

The virus takes a while to run its course. We don't know how many people die in the end. There's a huge number of people who have neither recovered not died yet. A lot of people focus on Diamond Princess, which was at <1% fatality late March. It's already up to 1.6% (the 12th passenger just died). 82 are still sick, of whom 9 are in severe condition. That's one of the first set of cases, so that's a lower bound with perfect medical care. Those 9 who are still in sever condition will almost certainly have permanent lung scarring. I'm not sure the status on the 82, but they've sick a long, long time -- we're now something like two months in.

Lower bound: Deaths/(total cases)

Upper bound: Deaths/(deaths + recovered)

Some media in France tend to focus on the upper bound, and reports numbers in the 10-30% range, so the country is very open to very severe measures. The US tends to be optimistic, and everyone plays it down, so the virus is spreading like wildfire.

On the other hand, I don't think "perfect medical care" is an accurate description of being quarantined on a boat with limited diagnostics and an illness your doctors have never seen before, and I also think the cruisegoing cohort skews much, much older than a general population.

Of course. As I said, you can try to paint a pretty picture, or an ugly picture. We don't know mortality rate very well yet (or much of anything else). Ever estimate has huge error bars in both directions, and the scientific estimates are sort of a median.

People in the US tend to look for every silver lining, preliminary study showing a potential breakthrough, and any reason it might not be so bad. That's a bias which has led to this not being taken seriously enough at any point.

I kind of treat the WHO estimates (1% with ventilator, 6% without, and 3.5% median) as just that: best-available estimates. It might be much, much worse. It might be much, much better.

"we calculated a median R0 value of 5.7"

My guess is that "median" covers that (without reading the paper)

Brazil is not testing enough, test results are being delayed 2-3 weeks. My sister works for one of the largest laboratories there (100+ labs across different states) and they are overwhelmed by supply shortages.

Current stats show 258 tests performed per 1 million inhabitants, compared to Germany's 15,730 per 1m pop. Brazil is testing almost the same as Togo (and 10x less than Iran) while having a bit over 60% of US's population.

Central and easter Europe is also lacking in total number of performed tests. You also have to take into account that there were more severe shutdown policies introduced. Since there is significantly less international travel in the east than in the west it was possible to isolate before covid hit with full might. Assessing the R0 depends a lot on the environment and countermeasures used.

The paper cites it's data mostly from spread in China.

This does not seem to be a WHO study, as far as I can tell?

Yeah, not sure where op got the "WHO" part of the title from, the site says: "Author affiliations: Los Alamos National Laboratory, Los Alamos, New Mexico, USA"

Based on Chinese data. I very much doubt the accuracy of Chinese data.

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