By Kwame Anthony Appiah
My wife and I are participating in a clinical trial for a Covid-19 vaccine. We had no antibodies before we received the vaccine, but we now have a lot of them, according to two independent tests. Presumably we are like millions of others who have recovered from Covid-19 and have these antibodies, and so are immune for some time.
At what point can I feel comfortable, ethically, not wearing a mask, being with others who haven’t had Covid, eating at a restaurant, going to a bar, traveling to locations with restrictions on “hot spot” visitors and the like?
I don’t want to be an “immune elite,” but I do want to begin a normal life again. Perhaps I have “earned” this by taking a risk and getting the vaccine? And perhaps others have “earned” this for having caught and recovered from the coronavirus? Name Withheld
First, thanks for volunteering for the clinical trial. We all owe a great deal to the many people around the world who are participating. But let’s not get out over our serological skis. If an antibody assay proved that you were immune to the coronavirus, there wouldn’t be any need to subject vaccine candidates to Phase III trials, which assess not just safety but also efficacy. Currently no vaccines for SARS-CoV-2 have completed these trials, which would establish that they significantly reduce a recipient’s chances of infection. The F.D.A. has said that approval will require a vaccine to show that it prevents infection or reduces its severity in at least 50 percent of those who receive it. Antibody results themselves wouldn’t suffice, according to F.D.A. guidance, because it isn’t yet known which antibodies at what levels are protective.
Let’s review a few more factual considerations. Specific antibodies target specific segments (“epitopes”) of a protein. The major American vaccine candidates, which focus on the coronavirus’s spike protein, might not give you as rich a complement of antibodies as those produced by someone who had actually been infected with the virus; the virus is more than its spikes. And acquired immunity doesn’t just arise from the antibodies in our serum; it involves white blood cells, such as killer T cells, that have been, in effect, trained to deal with the threat. As my medical colleagues remind me, recovered Covid-19 patients might be expected to have levels of cellular immunity that some vaccines may not trigger. (A few vaccines, notably one for HPV, may produce a better immune response than natural infection does, but usually it’s the other way around.) Going by available data, one well-funded vaccine candidate seems to produce only a weak cellular response. It might still work wonderfully well, but results in the test tube are no substitute for results in the field. And what’s expected of a good vaccine is that it would reduce your odds of infection (albeit in ways that, once vaccination is widespread, could lead to herd immunity), not that it would eliminate them.
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