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Antibodies Herd immunity Innovative Solutions Long-term effects

T-cells

Never thought my physiology degree would be worth anything. But here we are!

Our immune system has special types of cells with different functions: 1) B-cells (antibodies) latch on to the virus so they can’t enter the cells; 2) T-cells find and destroy the virus (and then remember who they need to destroy). T-cells have been found effective in MERS and SARS, but their role in COVID19 has not been clear.

One study in Singapore was just published on COVID19 t-cells. Briefly, they found:
• T-cell response is high among mild COVID19 cases (unlike the antibody studies we have seen)
• Interestingly, healthy people have COVID19 t-cells. This be due to exposure to other related coronaviruses, such as the common cold and SARS. This MAY explain why some people control the infection (and recover much better) than others.
• T-cells lasted over 17 years among SARS survivors, and the SARS t-cells WORK against COVID19

So far, all vaccines being developed target B-cells (antibodies), but scientists are starting to explore the potential of leveraging T-cells for therapeutic options. The problem is t-cells are much more complicated to analyze compared to antibodies. If fact, they require a special laboratory. So, we can’t do large population-based studies like we saw in Spain (https://yourlocalepidemiologist.com/?p=214).

To my knowledge, there are only three other published studies on this topic (regarding COVID19). I’ve included them below.

Love, your local epidemiologist

• Diao et al, 2020. https://pubmed.ncbi.nlm.nih.gov/32425950/
• Grifoni et al, 2020. https://pubmed.ncbi.nlm.nih.gov/32473127/
• Weiskopf et al, 2020. https://pubmed.ncbi.nlm.nih.gov/32591408/
•Le Bert et al., 2020 (Singapore study): https://www.nature.com/arti…/s41586-020-2550-z_reference.pdf

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Antibodies Herd immunity

Herd Immunity and Antibodies

This is my best shot at the current state of affairs regarding “natural” herd immunity and antibodies…

“Natural” COVID19 herd immunity is not only unethical, it is unattainable. There have been quite a few peer-reviewed studies to back this up:
• Santa Clara, CA: 3% of the population had antibodies (1,952 people)
• New York City: 14% (15,101 adult grocery shoppers)
• Sweden: 7.3% (1,100 people)
• France: 4.4% (projected)
• Spain: 4.6% (nation-wide study; 61,075 people; see Figure). This study was a VERY important step in science. This was country-wide study and participants represented all ages, sex, regions, income brackets, job types, number of household members. This level of diversity is very important when making generalizations.

Among those with a positive PCR test, nearly everyone makes antibodies:
• Spain: 90.1% of people with positive PCR had antibodies
• New York City: 99% of people with positive PCR had antibodies

Other important questions:
1. Accuracy of antibody tests? This varies depending on the test. For example, in the NY study, the antibody test had false negatives about 12% of the time and false positives less than 1% of the time. So, herd immunity is likely underestimated, but not by much.

2. Life of antibodies? There is very little evidence on this because not enough time has passed. However, the science is slowly coming out. Life of the antibodies seems to depend on how sick you got…
– Among asymptomatic people that DID have the antibody, 40% don’t have antibodies after 26 days (China study)
– Among sick people, 3% do not have antibodies 45 days later (another China study)
– If you don’t wait at LEAST one month (science says up to 50 days actually), your positive re-test is a reflection of your original infection, due to prolonged virus shedding, NOT a new infection.
– For other coronaviruses (like MERS and SERS) antibodies last 2-3 years. We can hope that a COVID19 vaccine with the right amount of immune response would act similar.

3. What is our herd immunity target? Estimates have ranged from 60-75% based on R(0) in March. A recent study even estimated as low as 43%.

Evidence is ever evolving. The rate in which the public wants information is incredibly fast for science, so be patient and flexible as more science comes out. In the meantime, appreciate the sheer amount of work conducted in the past 4 months. It’s absolutely incredible and a testament to scientists’ dedication to their communities.

Love, your local epidemiologist

Data sources:
Santa Clara study: https://jamanetwork.com/journals/jama/fullarticle/2766367
New York study: https://www.sciencedirect.com/…/artic…/pii/S1047279720302015
France study: https://science.sciencemag.org/…/early/2020/06/24/science.a…
Sweden study: https://www.folkhalsomyndigheten.se/…/forsta-resultaten-f…/…
Spain study: https://www.thelancet.com/…/PIIS0140-6736(20)31483…/fulltext
New York study (99% antibodies): https://www.medrxiv.org/conte…/10.1101/2020.04.30.20085613v1
China study (asymptomatic study): https://www.nature.com/articles/s41591-020-0965-6#Sec9
China study (re-test study): https://www.thelancet.com/action/showPdf…
Reinfection study: https://europepmc.org/article/ppr/ppr130524
43% herd immunity study: https://science.sciencemag.org/…/early/2020/06/22/science.a…