Coronavirus Game Changer? The Bendavid/Bhattacharya Study

 

A new study has just been released by Eran Bendavid, Jay Bhattacharya, and colleagues titled “COVID-19 Antibody Seroprevalence in Santa Clara County, California” (here).  You may remember Dr. Bhattacharya from Peter Robinson’s interview about 2 weeks ago (here).  This is the study that Dr. Bhattacharya discussed in Peter’s interview, of antibody testing that would establish the number of people who had been infected with COVID-19, which would allow us to estimate how many infections have gone undetected.

The short answer is: a lot.  The study estimates that the true number of infections in Santa Clara County is 50-85 times greater than the number reported from antigen testing (also called PCR-based testing).  The PCR or antigen testing determines whether a person has an active infection at the time of testing.  The antibody testing determines whether a person has previously been infected.  Santa Clara County, by the way, is the southern part of the San Francisco Bay area, centered on San Jose and including Stanford University and Silicon Valley.

Our discussion about this study started at Locke On’s post (here), at which our friend Mendel said that this “could be a genuine game changer.”  I concur.

In summary, Dr. Bendavid and his team tested 3,330 residents of Santa Clara County, on April 3-4.  They estimated that the prevalence of prior COVID-19 infection was 2.49%-4.16%.  This was “50-85-fold more than the number of confirmed cases” in the county.  They estimated an infection fatality rate (IFR) in the range of 0.12%-0.2%.

Note that this result is just for Santa Clara County, which is somewhat younger than the US as a whole.  According to the Census Bureau, 13.5% of Santa Clara County residents are 65 and over (here), compared to 16.0% nationally (here) and 14.1% in New York City (here).  Based on data from New York, about 75% of COVID-19 deaths have been to people 65 and over, so the IFR estimate for Santa Clara County would have to be adjusted upward somewhat, to be representative of the nation as a whole.

Adjusting for this difference in age distribution, I calculate an IFR for the nation as a whole in the 0.14%-0.23% range.

If this is correct, it implies a maximum death toll for the United States in the range of 320,000 to 530,000.  So no, we’re not looking at millions of deaths.  We’re looking at a much smaller figure — 425,000 as a point estimate — if the Bendavid study is solid information, as it appears to be.

[My calculations are as follows.  For the total deaths estimate, 330,000,000 population x 70% (herd immunity level) = 231,000,000 x IFR of 0.14%-0.23% = 323,400-531,300 deaths.  For the age-adjustment to the IFR, assume 75% of deaths to those 65 and over, so the Santa Clara County IFR of 0.12%-0.20% implies an IFR of 0.67%-1.11% for 65 and over, 0.035%-0.058% for under 65, then apply the overall US population ratios of 16.0% 65 and over, 84% under 65, and add the age subtotals, yielding 0.136%-0.226%.]

We can discuss the implications in the comments.

ChiCom delenda est.

 

 

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  1. Southern Pessimist Member
    Southern Pessimist
    @SouthernPessimist

    There are two other studies, which may have both been out of Boston, that suggest that the numbers of people exposed but asymptomatic might be quite high. The first homeless shelter which was sampled for active covid cases revealed 184  cases and all of them were asymptomatic. All of them. Another study of every woman coming for delivery in a large ob-gyn system found 15% positive and 84% asymptomatic with few serious symptoms in the others. The denominator is growing exponentially even if the virus is not.

    • #1
  2. Muleskinner, Weasel Wrangler Member
    Muleskinner, Weasel Wrangler
    @Muleskinner

    So in a related issue, does COVID-19 spread unnaturally fast, or has it been here longer than the ChiComs admit?

    • #2
  3. DonG (skeptic) Coolidge
    DonG (skeptic)
    @DonG

    I think herd immunity will happen at 30%, since we’ll make some lifestyle changes, especially so for the elderly.  Anti-viral treatments will also lower the death rate.  These advances in treatments and habits have to be factored in, but it is just guesswork. 

    • #3
  4. Southern Pessimist Member
    Southern Pessimist
    @SouthernPessimist

    Muleskinner, Weasel Wrangler (View Comment):

    So in a related issue, does COVID-19 spread unnaturally fast, or has it been here longer than the ChiComs admit?

    From what I have been able to glean from the limited information available is that the virus is spreading much faster than expected. I have not seen any information yet that the virus was infecting people here until January. The worst possible virus is one that spreads at high exponential rates but kills large numbers at a slower rate than its spread. That looked like the case early on, but although that is still somewhat true, the case mortality rate appears to be dropping into levels similar to h1n1 (swine flu) which was here in 2009. I believe that was the same virus responsible for the Spanish flu. H1N1 was more dangerous because it’s fatality was not restricted to elderly or otherwise compromised patients. It killed indiscriminately. Mrs. Pessimist was in an ICU for 10 days for H1N1 in 2009, while I had a bad cold.

    • #4
  5. Stina Inactive
    Stina
    @CM

    How hard is it to get and do this test?

    • #5
  6. Bob W Member
    Bob W
    @BobW

    I think the virus was in the central valley by the end of Dec. first of Jan. We have a lot of contact here with China due to the ag. industry through consulting and “something was going around”. My wife and I had several bad weeks then and what I had was unlike any cold or flu I have previously had. We didn’t think that we had Wuhan flu at the time because we really hadn’t heard about it. I didn’t see a doctor but my wife had to go to ER because she was having a hard time breathing one night. This was before any cases here so no flu test was done. Reading about the effects sure points to that virus and the Stanford testing adds. We are trying to find out how one of us could get the antibody test to be sure.

    I’ll post this on the other post too.

    • #6
  7. PHCheese Inactive
    PHCheese
    @PHCheese

    My son went to Los Vegas between Christmas and New Years he came home sick. He said Vegas was full of Chinese.

    • #7
  8. Spin Inactive
    Spin
    @Spin

    Similar study in the Seattle area:

    https://www.seattletimes.com/seattle-news/health/king-county-gets-new-glimpse-into-unreported-cases-of-covid-19-through-first-ever-swab-and-send-home-testing-kits/

    • #8
  9. Valiuth Member
    Valiuth
    @Valiuth

    Muleskinner, Weasel Wrangler (View Comment):

    So in a related issue, does COVID-19 spread unnaturally fast, or has it been here longer than the ChiComs admit?

    It seems that it is more infectious than the average flu. And compared to its cousins SARS and MERS it is far more infectious, though less deadly. 

    Sadly, I think the idea that it could only kill 450,000 will not comfort anyone. That would still be more people than our casualties in all 20th century wars put together dead in a single year. Plus it will hospitalize several times that number of people in critical condition. And of course as I mentioned in another thread, there are indications that not everyone who is infected becomes immune to the disease. Reports out of South Korea indicate that some people who have had the disease can become reinfected. So even if everyone gets it it won’t mean it goes away. Based on its level of infectivity it may take +80% of the population being immune to create a herd immunity effect (The more infectious the disease the higher the percentage of population needs to be immune to stop spread). 

    • #9
  10. Western Chauvinist Member
    Western Chauvinist
    @WesternChauvinist

    It irritates me no end that we’ve been hearing speculation from “the experts” on the death rate when we don’t even know the dang denominator!!! Where is the intellectual humility??

    Repeat the three (four) most important words in science: “We don’t know.” Dr. Fauci with his “10x the death rate of the flu” should go first. Nobody knows nuthin’. But, we’re learning. In the meantime, Fauci and friends should not damage their “expert” credibility with such wild half-assed guesses. 

    • #10
  11. rgbact Inactive
    rgbact
    @romanblichar

    Reminder…even the Ferguson models that kicked off all the craziness were only estimating a 0.5% mortality rate. So, hopefully most are aware that the ultimate mortality rate wasn’t going to be 3%+. But, Ferguson estimated that nearly everyone got it….hence, lots of deaths. So….why does only 3% of Santa Clara County have it…..if everyone is eventually supposed to get it, even people in much less urban areas?

    Also curious if there are estimates of the mortality rate for flu without a vaccine.

     

    • #11
  12. Jerry Giordano (Arizona Patrio… Member
    Jerry Giordano (Arizona Patrio…
    @ArizonaPatriot

    Valiuth (View Comment):

    Muleskinner, Weasel Wrangler (View Comment):

    So in a related issue, does COVID-19 spread unnaturally fast, or has it been here longer than the ChiComs admit?

    It seems that it is more infectious than the average flu. And compared to its cousins SARS and MERS it is far more infectious, though less deadly.

    Sadly, I think the idea that it could only kill 450,000 will not comfort anyone. That would still be more people than our casualties in all 20th century wars put together dead in a single year. Plus it will hospitalize several times that number of people in critical condition. And of course as I mentioned in another thread, there are indications that not everyone who is infected becomes immune to the disease. Reports out of South Korea indicate that some people who have had the disease can become reinfected. So even if everyone gets it it won’t mean it goes away. Based on its level of infectivity it may take +80% of the population being immune to create a herd immunity effect (The more infectious the disease the higher the percentage of population needs to be immune to stop spread).

    Val, I don’t dispute that it’s going to be rather bad, but there’s little to be done, and what we’re doing does more harm than good.  We could probably make it better with severe restrictions on the elderly, and the (very small number) of non-elderly who are at special risk.

    I don’t think that the 80% figure is likely.  This would imply a R0 of about 5, since the herd immunity formula is 1 – 1/Ro (I think).

    The R0 estimates for COVID-19 have ranged around 2.5-3.5, which implies herd immunity at around 60%-69%.  This is why I used 70%, to be a bit on the conservative side.

    • #12
  13. Jerry Giordano (Arizona Patrio… Member
    Jerry Giordano (Arizona Patrio…
    @ArizonaPatriot

    DonG (skeptic) (View Comment):

    I think herd immunity will happen at 30%, since we’ll make some lifestyle changes, especially so for the elderly. Anti-viral treatments will also lower the death rate. These advances in treatments and habits have to be factored in, but it is just guesswork.

    To be at 30%, we’d have to get R0 down to around 1.4.  This might be feasible in the short-term, but probably not in the long-term.

    • #13
  14. Gumby Mark (R-Meth Lab of Demo… Coolidge
    Gumby Mark (R-Meth Lab of Demo…
    @GumbyMark

    Jerry Giordano (Arizona Patrio… (View Comment):

    Valiuth (View Comment):

    Muleskinner, Weasel Wrangler (View Comment):

    So in a related issue, does COVID-19 spread unnaturally fast, or has it been here longer than the ChiComs admit?

    It seems that it is more infectious than the average flu. And compared to its cousins SARS and MERS it is far more infectious, though less deadly.

    Sadly, I think the idea that it could only kill 450,000 will not comfort anyone. That would still be more people than our casualties in all 20th century wars put together dead in a single year. Plus it will hospitalize several times that number of people in critical condition. And of course as I mentioned in another thread, there are indications that not everyone who is infected becomes immune to the disease. Reports out of South Korea indicate that some people who have had the disease can become reinfected. So even if everyone gets it it won’t mean it goes away. Based on its level of infectivity it may take +80% of the population being immune to create a herd immunity effect (The more infectious the disease the higher the percentage of population needs to be immune to stop spread).

    Val, I don’t dispute that it’s going to be rather bad, but there’s little to be done, and what we’re doing does more harm than good. We could probably make it better with severe restrictions on the elderly, and the (very small number) of non-elderly who are at special risk.

    I think we do need to be lifting society wide lockdowns, but the number who remain vulnerable and may require continuing severe restrictions is substantial.  Let’s start with the 50 million Americans 65 and older.  Then we have the three most widespread risk factors, diabetes, hypertension, and obesity.  I can’t locate directly comparable information on all three but what I did find was that there are 20 million Americans younger than 65 with diabetes; about 20% of Americans between the ages of 20 and 54 have hypertension; and, as for obesity, in those younger than 65 just take a look around.  While there may be substantial overlap between 2 or all 3 of these conditions it could easily be that 25% of Americans will still severely restricted.  If you add in those outside these categories who are still going to be reluctant to patronize certain stores, events, and business sectors like aviation it’s why I think in the best of cases, even without lockdowns, we will have a severe recession and my hope is to avoid a depression.

    • #14
  15. Jerry Giordano (Arizona Patrio… Member
    Jerry Giordano (Arizona Patrio…
    @ArizonaPatriot

    rgbact (View Comment):

    Reminder…even the Ferguson models that kicked off all the craziness were only estimating a 0.5% mortality rate. So, hopefully most are aware that the ultimate mortality rate wasn’t going to be 3%+. But, Ferguson estimated that nearly everyone got it….hence, lots of deaths. So….why does only 3% of Santa Clara County have it…..if everyone is eventually supposed to get it, even people in much less urban areas?

    Also curious if there are estimates of the mortality rate for flu without a vaccine.

     

    The ICL (Ferguson) model assumed a 0.9% IFR, not 0.5%.  See here.

    • #15
  16. Roderic Coolidge
    Roderic
    @rhfabian

    Jerry Giordano (Arizona Patrio…: If this is correct, it implies a maximum death toll for the United States in the range of 320,000 to 530,000. So no, we’re not looking at millions of deaths. We’re looking at a much smaller figure — 425,000 as a point estimate — if the Bendavid study is solid information, as it appears to be.

    The proportion of the sample with a positive result was 1.5%, which is in the range of false positive rates for this type of test.   They mention that the assay was tested against 30 positive and 30 negative controls.  If the results from that were perfect the best you can say is that the false positive rate is below 10%.

    I’m disappointed that the proportion wasn’t a lot higher than that.  As it is, this is not enough to conclude that there are a lot of asymptomatic cases out there, although there’s other evidence that might be the case; i.e. 7 times as many asymptomatic as symptomatic patients in one group.

    • #16
  17. rgbact Inactive
    rgbact
    @romanblichar

    Gumby Mark (R-Meth Lab of Demo… (View Comment):

    Let’s start with the 50 million Americans 65 and older. Then we have the three most widespread risk factors, diabetes, hypertension, and obesity. I can’t locate directly comparable information on all three but what I did find was that there are 20 million Americans younger than 65 with diabetes; about 20% of Americans between the ages of 20 and 54 have hypertension; and, as for obesity, in those younger than 65 just take a look around. While there may be substantial overlap between 2 or all 3 of these conditions it could easily be that 25% of Americans will still severely restricted.

    So, 75% unrestricted gets us pretty far, especially since  only 60% of seniors even work. Age 55-64, with diabetes/hypertension will be a question mark. That leaves lots of others to run the economy.

    • #17
  18. JuliaBlaschke Lincoln
    JuliaBlaschke
    @JuliaBlaschke

    Muleskinner, Weasel Wrangler (View Comment):

    So in a related issue, does COVID-19 spread unnaturally fast, or has it been here longer than the ChiComs admit?

    Yes. Both.

    • #18
  19. Unsk Member
    Unsk
    @Unsk

    Western Chav: “It irritates me no end that we’ve been hearing speculation from “the experts” on the death rate when we don’t even know the dang denominator!!”

    Jerry, Umm, Maybe I’m just stupid but it would seem to me if the number of those who are now or have been infected is 50 to 80 times greater than those testing positive, shouldn’t we radically adjust downward the expected death rate from COVID-19?

    If you assume,being prudent,  a 2% death rate among those testing positive, which is in  actuality I think grossly exaggerated at this point, the number that have died as a percentage of those who are now or have been infected is something less than 0.04%, if one assumes that there are 50 times minimum those testing positive that are or have been infected. I don’t think one can take an arbitrary number of deaths per infected based upon deaths of those testing positive and apply that percentage to those many more who have not tested positive but may be or have been infected nonetheless to come up with a number even close to 425,000 deaths. The facts appear to be that thousands have had the disease without showing symptoms or testing positive and did not die so that reality should affect the denominator of the total infected without affecting the numerator of those who died, to use Western Chav’s point which  would make the anticipated death rate a very, very  low number.   

    And that analysis doesn’t even take into account that its seems  major jurisdictions like almost all in my state of California  I think are juicing the numbers in a big way to spread panic to justify the their diabolical lockdowns with deaths that have occurred in a person that had  major life threatening health issues and whose deaths  now are  almost all  being attributed solely to COVID-19 whether that was anything close to the true cause of death or not. 

    • #19
  20. Jerry Giordano (Arizona Patrio… Member
    Jerry Giordano (Arizona Patrio…
    @ArizonaPatriot

    JuliaBlaschke (View Comment):

    Muleskinner, Weasel Wrangler (View Comment):

    So in a related issue, does COVID-19 spread unnaturally fast, or has it been here longer than the ChiComs admit?

    Yes. Both.

    I’m not sure if it’s unnaturally fast.  It’s pretty fast, but my impression is that this is pretty common with a respiratory virus.  I don’t actually know how fast a common cold spreads.  Wikipedia lists it with a R0 of 2-3, which is the same general range as COVID-19, though there is more uncertainty for COVID-19 and it might be higher.

    • #20
  21. Valiuth Member
    Valiuth
    @Valiuth

    rgbact (View Comment):

     

    Gumby Mark (R-Meth Lab of Demo… (View Comment):

    Let’s start with the 50 million Americans 65 and older. Then we have the three most widespread risk factors, diabetes, hypertension, and obesity. I can’t locate directly comparable information on all three but what I did find was that there are 20 million Americans younger than 65 with diabetes; about 20% of Americans between the ages of 20 and 54 have hypertension; and, as for obesity, in those younger than 65 just take a look around. While there may be substantial overlap between 2 or all 3 of these conditions it could easily be that 25% of Americans will still severely restricted.

    So, 75% unrestricted gets us pretty far, especially since only 60% of seniors even work. Age 55-64, with diabetes/hypertension will be a question mark. That leaves lots of others to run the economy.

    But work isn’t the main risk factor for spread. Seniors will have to get food, buy clothes, go to church. The points where the young <65 meet people>65 are numerous. If the young become widely infected the risk to the old picking it up form them jumps significantly since you can’t possibly contain them that tightly. Do we think we could now isolate the elderly and at risk more than they are being now? I’m skeptical of that. People are already out there running the economy at leas the essentials we haven’t run out of food. But, how much business do you think a theater will actually get? Or a restaurant? How much do you think people in cities will want to crowd onto buses and trains to commute to work in a clothing store where foot traffic will be down by 50%? And then if cases and deaths spike back up as social distancing is eased up what will be the social response? The political fall out? People might be eager to get back to work, but will they feel confident that we have the virus under control? Do we have it under control? I’m skeptical of that. The guidelines for reopening seem reasonable at first glance, but I don’t see an assessment of where every state is at.  And Trump’s own erratic position on the issue does not feel me with confidence. I’m sure I’m not alone. 

    • #21
  22. rgbact Inactive
    rgbact
    @romanblichar

    Valiuth (View Comment):

    rgbact (View Comment):

    So, 75% unrestricted gets us pretty far, especially since only 60% of seniors even work. Age 55-64, with diabetes/hypertension will be a question mark. That leaves lots of others to run the economy.

    Do we think we could now isolate the elderly and at risk more than they are being now? I’m skeptical of that. People are already out there running the economy at leas the essentials we haven’t run out of food. 

    Sweet. Its 20% unemployment, but at least we have basic food. Sounds like a plan.  If seniors are restricted….how are the points that people meet then “numerous”. Thats the whole point of some people being restricted.

    • #22
  23. Hoyacon Member
    Hoyacon
    @Hoyacon

    Rush is now discussing the study, and would have been well-served to read the discussion here.

    • #23
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