Why COVID-19 herd immunity may be closer than we think

There is an opinion piece in The Wall Street Journal that says that we are closer to herd immunity than we know. It argues that if you look at the T cells — the cells that remember past infections — we will find that quite a few people have developed an immunity to COVID-19 without ever having had any symptoms.

Mercer Island MD Dr. Gordon Cohen joined Seattle’s Morning News to discuss.

“One of the things that’s been largely ignored amongst all these dire COVID warnings is the fact that COVID cases are down 77% over the past six weeks. So this opinion piece by Dr. Marty Makary — who’s a well known surgeon and public health expert — he says that ‘if a medication slashes cases by 77% we call it a miracle pill.’ So he poses the question: Why is the number of cases plummeting? And it has to do with the different types of immunity our body has, antibodies versus T cells,” Dr. Cohen said.

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According to that theory, the numbers behind the mortality rate and the infection rate seem to indicate a wider spread herd immunity than originally thought.

“When we’re doing antibody testing, it doesn’t capture these antigen specific T cells or memory T cells once they’re activated by the virus. And it’s quite interesting that he points out that people who survived the 1918 Spanish flu were found in 2008 — 90 years later — to have memory T cells that were still able to produce neutralizing antibodies,” he said.

“So what he’s saying is about one in 600 Americans has died of COVID-19, which translates to a population fatality rate of about 0.15%. So that’s what the theoretical mortality rate is of COVID-19. But the current COVID-19 infection fatality rate is 0.23%. So these numbers actually suggest that roughly two-thirds of the United States population has actually already had the infection (potentially without knowing it).”

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In other words, the testing that’s been done is testing the antibodies that are currently fighting the infection. Once those antibodies disappear, the T cells are left to remember that infection, and those are the ones that actually protect you from the future infection. But the tests do not reveal their existence.

“That’s how our body naturally develops immunity. But when we’re testing people to see if they have a response to the vaccination, we’re testing for antibodies, we’re not testing for T cell activity. So what he’s pointed out is by using a variety of mathematical models, it is possible that by April, based on his mathematical data and what we do know about the disease, that largely COVID-19 may be mostly gone,” Dr. Cohen said.

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