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Covid-19 Antibody Seroprevalence in Santa Clara County, California

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Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#141

Post by lmlsna »

kaikai wrote: post #113
tom-thistime wrote: post #96

Earlier quoted context omitted.

Most of what I've seen suggests that at time of positive test results, 40% to 70% of people have not experienced symptoms. Have you seen numbers very different from that? [Edit: 'No symptoms experienced at time of positive test results' is intended to mean the same as 'no symptoms experienced yet at time of positive test results'.]

Have not experienced symptoms yet. I haven't seen any information about testing people and then following through until a negative test, to see whether they stay asymptomatic. It's more likely that we're testing them in the window between being infected and showing symptoms.

Confirmed population infection rate in Santa Clara is like 0.1%, and has been on a stay at home order for a month.

Highly unlikely these are all just people who have produced antibodies as part of a yet-to-be overrun immune response.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#142

Post by OatMilkLatte »

MiguelVieira wrote: post #109
erentz wrote: post #79

It’s hacky and I’m happy to be told how wrong it is. But based on these recent antibody studies in Germany, Finland, and now here in CA, I’ve been assuming an actual fatality rate of about 0.4, and thus an actual infected rate of 250x our known deaths, which is a much firmer number. This is only a small comfort since it means we may have had about 8.75 million infected and presumably now immune in the USA. Or about 2…

I've been using 0.5% for mental math, rounding down from the lower bound from this study in The Lancet: https://www.thelancet.com/journals/laninf/article/PIIS1473-3... I would be surprised if, after this current wave of infections, the percentage of people with antibodies in the US is higher than the low single digits. Herd immunity without a vaccine is a pipe dream. Our best bet is to massively ramp up testing and c…

> Herd immunity without a vaccine is a pipe dream. Our best bet is to massively ramp up testing and contact tracing and really start pushing the number of infections down to a point where parts of society can start functioning again.

The problem is, a vaccine is also a pipe dream. So we're going to have to all get infected over some sort of timeline that doesn't cause societal collapse. Also known as flattening the curve.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#143

Post by irq11 »

cameldrv wrote: post #103
cuchoi wrote: post #8

Caveat from the paper: "This study had several limitations. First, our sampling strategy selected for members of Santa Clara County with access to Facebook and a car to attend drive-through testing sites. This resulted in an over-representation of white women between the ages of 19 and 64, and an under-representation of Hispanic and Asian populations, relative to our community. Those imbalances were partly addressed…

Yes, and look at the way they corrected for this. They rebalanced for demographics, and that doubled their estimate. This is exactly the opposite of what they should have done. For example, zip codes farther from the testing sites were less likely to get tested, and more likely to be positive. What you see is that certain groups were less likely to go get tested, UNLESS they had a good reason to think that they were…

That is just nonsense. You don’t adjust for demographic bias in a sample by conditioning on a second parameter. There’s no universe in which underweighting the underweighted group makes any sense at all. Moreover, there isn any support for the idea that “bored white women” are more or less likely to get tested for symptomatic illness than anyone else.

Your entire argument boils down to “I don’t like the implications of their adjustment, and this other one would have produced results more consistent with my theories.”

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#144

Post by Animats »

erentz wrote: post #79

It’s hacky and I’m happy to be told how wrong it is. But based on these recent antibody studies in Germany, Finland, and now here in CA, I’ve been assuming an actual fatality rate of about 0.4, and thus an actual infected rate of 250x our known deaths, which is a much firmer number. This is only a small comfort since it means we may have had about 8.75 million infected and presumably now immune in the USA. Or about 2…

There’s still a long way to go in that case.

Yes. Stanford's recent study says 2-4% of the population of Santa Clara County has been infected. Those are probably reasonable bounds. Herd immunity is around 80% for this. So about 20 to 40 times as many people need to die before it's over.

That test needs to be repeated weekly to get the growth rate. (Preferably not with the scheme from Verity, which requires that you sign up for a Google account.[1]) Now that California hospital admissions and deaths for COVID-19 have flattened, growth should be linear for a while. But the rate of increase is still not really known.

Still, we're probably looking at a year and a million deaths in the US, within a factor of 2 either way.

[1] https://verily.com/stories/the-project-baseline-covid-19-pro...

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#145

Post by irq11 »

joe_the_user wrote: post #130
MiguelVieira wrote: post #109

Earlier quoted context omitted.

I've been using 0.5% for mental math, rounding down from the lower bound from this study in The Lancet: https://www.thelancet.com/journals/laninf/article/PIIS1473-3... I would be surprised if, after this current wave of infections, the percentage of people with antibodies in the US is higher than the low single digits. Herd immunity without a vaccine is a pipe dream. Our best bet is to massively ramp up testing and c…

So a 0.5% fatality rate sounds like "only" five times the rate of the flu. EXCEPT that I would bet that if you thoroughly traced all the asymptomatic but positive for the flu, it's fatality rate would decline also and it still causes significant deaths. Total Covid deaths are already at a "mild flu season" level already after a month and continuing some level of exponential growth after social distancing. It's sad an…

Except that a huge portion of those deaths are in places that may have already reached herd immunity, if the ratio of comfirmed / actual cases is as small as this study suggests.

NYC, for example, has 123k confirmed cases. Multiply by 50, and you have 6.1M, which is close to 70% of the total population.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#146

Post by grandmczeb »

shalmanese wrote: post #112
georgewfraser wrote: post #31

There are now multiple sources of evidence pointing to a very low true infection fatality rate, as low as 0.1% in some regions. Iceland has been testing a semi-random sample using PCR since early in the epidemic, and there have been several small antibody surveys in “hot spots” showing infection rates over 15%. You can also use CDC surveillance of flu-like illnesses to estimate the total number of infected nationwide…

How do you square this with 0.14% of all of NYC and 0.25% of all of Bergamo county being dead from confirmed Coronavirus? Surely this puts a strong lower limit on IFR. Deaths in both places can only increase and deaths will inevitably be retroactively assigned a Coronavirus cause.

A large percentage of the population in NYC and Italy have been probably already been infected -- for NYC specifically, I don't think its too implausible to imagine 20-30%. That would give an IFR of ~0.6% which is in line with a lot of other estimates. An IFR of <0.3% seems unlikely though.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#147

Post by irq11 »

usaar333 wrote: post #117
brink wrote: post #82

Earlier quoted context omitted.

I know. 50-85x is hard to believe. How could we be that far off?

It's impossible to believe. Currently, Santa Clara's crude CFR is 3.7%. NYC has similar demographics (and as bad nursing home hits?) -- 0.14% of the population has died from covid. That puts an upper bound of 26x (and that's if the entire population was infected)

You have no reason to believe that the Santa Clara CFR is correct, and dividing the CFR of one city by the IFR of another is meaningless.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#148

Post by grandmczeb »

projektfu wrote: post #49
georgewfraser wrote: post #31

There are now multiple sources of evidence pointing to a very low true infection fatality rate, as low as 0.1% in some regions. Iceland has been testing a semi-random sample using PCR since early in the epidemic, and there have been several small antibody surveys in “hot spots” showing infection rates over 15%. You can also use CDC surveillance of flu-like illnesses to estimate the total number of infected nationwide…

It may have a low overall fatality rate, yet it seems to have a high rate of hospitalization in clinical cases.

> it seems to have a high rate of hospitalization in clinical cases.

The raw hospitalization rate is inflated because both treatment and testing are mostly limited to very severe cases in places where there's a lot of confirmed cases (e.g. NYC.)

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#149

Post by projektfu »

grandmczeb wrote: post #148
projektfu wrote: post #49

Earlier quoted context omitted.

It may have a low overall fatality rate, yet it seems to have a high rate of hospitalization in clinical cases.

> it seems to have a high rate of hospitalization in clinical cases. The raw hospitalization rate is inflated because both treatment and testing are mostly limited to very severe cases in places where there's a lot of confirmed cases (e.g. NYC.)

Still, comparing it to influenza... we dont see this many severe cases typically.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#150

Post by wk_end »

joe_the_user wrote: post #130
MiguelVieira wrote: post #109

Earlier quoted context omitted.

I've been using 0.5% for mental math, rounding down from the lower bound from this study in The Lancet: https://www.thelancet.com/journals/laninf/article/PIIS1473-3... I would be surprised if, after this current wave of infections, the percentage of people with antibodies in the US is higher than the low single digits. Herd immunity without a vaccine is a pipe dream. Our best bet is to massively ramp up testing and c…

So a 0.5% fatality rate sounds like "only" five times the rate of the flu. EXCEPT that I would bet that if you thoroughly traced all the asymptomatic but positive for the flu, it's fatality rate would decline also and it still causes significant deaths. Total Covid deaths are already at a "mild flu season" level already after a month and continuing some level of exponential growth after social distancing. It's sad an…

I’m not a virologist or epidemiologist, so I might be off-base here, but: the flu’s really well understood isn’t it? Medicine’s been studying it basically forever. I’d be really surprised if our fatality rate for it wasn’t pretty accurate and didn’t already have asymptomatic cases factored in.
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