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Immunity Update: We have more data on why people exposed to COVID dont seem to get COVID. @ASlavitt

1. Immunity from unrecognized prior infection:
Up to 80% of COVID is asymptomatic. Most are missed unless PCR test is done at right time. Serology normalizes quickly in 40%
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2. Cross immunity from prior corona virus infections: We thought everyone is susceptible coz its a new virus. A naive interpretation that didn’t recognize how promiscuous immune responses can be. T cells reactive to SARS CoV-2 have been found in persons never exposed to COVID
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3. Decreased susceptibility to COVID due to certain genetic factors:

~30% Lesser risk of infection in people with Blood group O.

Also study of 2 sets of young twins that showed mutations in TLR7 greatly increased severity— means there is a world to discover on predisposition.
4 False negative tests: Many tests in use aren’t the greatest. Both for detecting infection or for detecting history of infection. So someone could actually have symptomatic COVID and is told they don’t have it. nejm.org/doi/full/10.10…
5. Non specific protection because of prior vaccines: not sure of this. There are studies showing some protection because of prior MMR vaccine or BCG vaccines. mbio.asm.org/content/11/3/e…
6. Effective precautionary measures:

This is the BIG one. By wearing masks, distancing, proper hand hygiene as a way of life, you could prevent getting COVID even if you were exposed to it. Since we can’t take chances, we absolutely need to be safe. @jeremyphoward #Masks4All
These 6 things explain the marked drop offs in the enumerated COVID cases in many hotspots that we are seeing despite seroprevalence that’s much lower than the usual 70% threshold for herd immunity. These places are still at risk, coz there are still a lot of susceptible people.
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Vincent Rajkumar
@VincentRK
I read this book 30 years ago as a young medical student. The book is full of stories like the ones you hear today about Hyydroxychloroquine.

Uncontrolled studies and anecdotes showing dramatic cures of over 100 different diseases with one single drug!! Phenytoin!

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I was so amazed when I read it. I truly believed that this remarkable drug had been overlooked.

Luckily I was introduced (by Dr. Alan Gijsbers) to these two books which taught me how easy it is to be fooled by anecdotes and non randomized drug trials.

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As a young medical student the effect of these two books on my approach to medicine, and my subsequent academic success cannot be overstated. I would recommend that all medical students read these two books.

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Vincent Rajkumar
@VincentRK
The COVID Strategies

1) China: COVID started there but they have successfully made it a foreign virus. How? Basically walling off Hubei, then aggressive testing and contact tracing, quarantine, & masks. At the same time they sealed borders to stop reentry of virus.
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2) New Zealand: They knew COVID was a foreign invader. They acted early with aggressive border control. They kept virus out of the country at all costs. Now life is normal. Their game plan is to sustain this till there’s a vaccine. @ASlavitt
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3) Sweden: They didn’t think they could seal borders in time or afford a lockdown. Strategy: Allow near normal life and get to herd immunity. They lost more people than they should have. Economical no better off than neighbors. But close to herd immunity by paying a high price
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Vincent Rajkumar
@VincentRK
COVID Vaccines

1) A vaccine doesn’t need to prevent infection altogether. It just needs to prevent severe disease and/or deaths.

2) Antibody levels may not correlate with efficacy

3) T cell responses occur. May not prevent infection, but can protect against severe disease.
4) There is old data with the measles vaccine in 6 month olds, where there is no significant antibody formation at that age, but T cells are generated, and were found capable of preventing severe disease and deaths.
5) T cells are likely involved in cross immunity.

6) T cells reactive to SARS CoV-2 have are also found in people with exposure but are antibody negative.

7) T cell/Cross immunity likely contributes to the reduction in cases, & case severity we see in many parts of the world
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