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. https://www.nejm.org/doi/full/10.1056/NEJMp2015897

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. https://mbio.asm.org/content/11/3/e00907-20?_ga=2.14862134.1229309379.1595896940-1320609374.1595896940

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.