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:
New York study:…/artic…/pii/S1047279720302015
France study:…/early/2020/06/24/science.a…
Sweden study:…/forsta-resultaten-f…/…
Spain study:…/PIIS0140-6736(20)31483…/fulltext
New York study (99% antibodies):…/10.1101/2020.04.30.20085613v1
China study (asymptomatic study):
China study (re-test study):…
Reinfection study:
43% herd immunity study:…/early/2020/06/22/science.a…

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