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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

#51

Post by _9vpl »

pwned1 wrote: post #5
h2odragon wrote: post #3

I think the numbers will coma out to show this ripped through the USA in February; we slammed the barn doors closed well after the horse was gone. Of course that's not the narrative that fits agendas so just like with "why cant we test people?" back then, there will be many official reasons not to look for antibody data and to doubt what data gets gathered.

Based on the difference between CA and NY, I'd be willing to bet that it got here earlier, maybe in December.

I think the more likely explanation is that NY simply is a lot more dense and less reliant on cars vs the less dense and more reliant on cars California.

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

#52

Post by [deleted] »

DennisP wrote: post #9

The problem with every one of these studies I've seen is that they come up with around 3% of the population having antibodies, while a typical false-positive rate for these tests is also around 3%. In this case they claim they adjust for the specificity (basically false-positive rate), but I didn't see that they reported what the specificity was. If the mortality really is very low, then it should be easy to prove. J…

[deleted]

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

#53

Post by dragonwriter »

dmitriy_ko wrote: post #44
sxp wrote: post #14

There are similar high infection rates from other semi-randomized samples. https://www.nejm.org/doi/full/10.1056/NEJMc2009316 > Between March 22 and April 4, 2020, a total of 215 pregnant women delivered infants at the New York–Presbyterian Allen Hospital and Columbia University Irving Medical Center . All the women were screened on admission for symptoms of Covid-19. Four women (1.9%) had fever or other symptoms of…

So 15% infection rate among pregnant women. I would assume pregnant women would be more careful than average about avoiding getting infected. So overall infection rate in New York City must be even higher.

> So 15% infection rate among pregnant women. I would assume pregnant women would be more careful than average about avoiding getting infected.

Pregnant women would seem to be much less able to avoid certain activities that involve transmission (like visiting medical facilities and associated close contact with people who also work in hospitals with inadequate and improvised PPE), so that’s probably not a great assumption.

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

#54

Post by timr »

cdelsolar wrote: post #43
timr wrote: post #39

Earlier quoted context omitted.

"If the epidemic is more widespread than initially thought, why do you assume that the effective transmission rate would potentially decrease?" Herd immunity. If testing is only detecting 1/50th of cases in NYC, for example, it means that there have been about 6M cases, or about 69% of NYC's population. That's basically the threshold where we'd expect to see the infection counts level off naturally.

there is no herd immunity if reinfection can occur, which appears to be the case

There is no credible scientific evidence that reinfection can occur. There have been, at most, anecdotal reports from unreliable sources.

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

#55

Post by BearOso »

In our small town, I know of 3 people who came into direct contact with the first confirmed case, exhibited symptoms, but were refused testing. I can definitely believe their guess that the number of cases is an order of magnitude greater than the number confirmed.

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

#56

Post by [deleted] »

gryson wrote: post #37
not2b wrote: post #30

Earlier quoted context omitted.

Yes, the ads accurately described the study. Several friends of mine participated (I live in Santa Clara County). Of course there is selection bias, which is why they make adjustments to make the sample better represent the population (see the abstract for details on this, or read the paper for all the details, there's well-established science behind these adjustments and it's up to the reviewers to be sure that they…

What adjustments were made to account for selection bias of the sort described? It's not covered in the paper, and "well-established science" certainly doesn't answer the question.

[deleted]

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

#57

Post by tshadley »

rhema wrote: post #33
tshadley wrote: post #26

Earlier quoted context omitted.

Why would this matter as long as they got a good geographical sampling? "We used Facebook to quickly reach a large number of county residents and because it allows for granular targeting by zip code and sociodemographic characteristics. We used a combination of two targeting strategies: ads aimed at a representative population of the county by zip code, and specially targeted ads to balance our sample for under-repre…

If part of the value for participants was to know whether they had antibodies, then those that had gone through a flu (or covid) would be more likely to respond. This means that the overall sample likely includes more people who had COVID than a true random sampling would.

It looks like there's an argument to be made it could overcount or undercount depending on importance of each potential bias.

"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 overrepresentation 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 by weighting our sample population by zip code, race, and sex to match the county. We did not account for age imbalance in our sample, and could not ascertain representativeness of SARS-CoV-2 antibodies in homeless populations. Other biases, such as bias favoring individuals in good health capable of attending our testing sites, or bias favoring those with prior COVID-like illnesses seeking antibody confirmation are also possible. The overall effect of such biases is hard to ascertain."

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

#58

Post by tomerico »

compiler-guy wrote: post #50
gryson wrote: post #37

Earlier quoted context omitted.

What adjustments were made to account for selection bias of the sort described? It's not covered in the paper, and "well-established science" certainly doesn't answer the question.

These are very common statistical methods when dealing with surveys and populations. It isn't this paper's job to describe the background on something like that, just like it isn't this papers job to explain blood testing. They describe their limitations and adjustments exactly like most other studies of this sort do. For example: "Those imbalances were partly addressed by weighting our sample population by zip code,…

They said that they collected prior clinical symptoms in the survey, but have not mentioned that they adjusted for those.

Given that, I think it's fair to say that they have not adjusted for the selection bias of people with prior clinical symptoms being more likely to click the ad.

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

#59

Post by MikeAmelung »

slg wrote: post #46
pwned1 wrote: post #36

Earlier quoted context omitted.

Maybe a milder form of it came directly from Wuhan to CA, spreading like a bad flu. And then the version in NY came from Wuhan to Europe to NY, mutating along the way, and making it more deadly.

I'm not sure why we should believe the strain that originated in Wuhan was milder, but lets go with this theory for a minute. How does the nursing home in Washington fit into that picture? It was one of the earliest known hotspots in the US and it was extremely deadly. Was it the mild strain that you think might have already been spreading through California or the severe strain from Europe that spread to Washington…

Not that I necessarily agree with the theory, an influenza outbreak in a nursing home could be extremely deadly. This is why they are nearly 100% vaccinated. And they are (or are supposed to be) quick to quarantine and lockdown if it seems like flu has been detected. Which is to say that even a "mild" strain would certainly pose a larger risk to a nursing home.

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

#60

Post by DanBC »

microdrum wrote: post #47
cdelsolar wrote: post #45

Earlier quoted context omitted.

nope.

Yep. You've got nothing. CFR is low, and this has been knowable for a long time. You're scared. It's OK. It's illogical and anti-scientific, but it's OK. But you won't be able to hurt ordinary people any longer. Here's Germany's imputed CFR: https://spectator.us/covid-antibody-test-german-town-shows-1... Here's Denmark: https://www.dr.dk/nyheder/indland/doedelighed-skal-formentli... Here's Iceland: https://reason.com…

Why quote Denmark but ignore Sweden? Sweden are doing what you're calling for, and they have pretty high numbers of deaths.
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