"Your Coronavirus Antibodies Are Disappearing. Should You Care?" by Apoorva Mandavilli tells the very interesting story of how antibodies actually work and why the prevalent antibody tests are so bad at detecting them.
According to Ms. Mandavillli, an investigative medical science journalist,
After the battle with the pathogen is over, the number of antibodies drops off. However, cells in the bone marrow will continue to pump out a small quantity of "specialized assassins," as Ms. Mandavilli refers to the antibodies, lying in wait for their "specific targets." Should the antibodies detect another incursion by their target pathogen,
And though the coronavirus started out as a stranger to scientists, which is why the narrative on immunity seems to be constantly shifting, as it is studied more it's becoming "increasingly clear that this virus behaves much like any other."
Furthermore, in the very unlikely event that a person who had COVID19 didn't develop antibodies, they would still have cellular immunity, which involves "T cells that learn to identify and destroy the virus." According to several recent studies, "Virtually everyone infected with the coronavirus seems to develop T-cell responses."
Now, to the problem - make that problems - with the coronavirus antibody tests.
First of all, most of the commercial coronavirus antibody tests being used in the United States are not finely calibrated enough to pick up the low levels of antibodies present after one has recovered from the virus. Therefore these tests are notorious for giving false negatives. They are also, for some reason, notorious for giving false positives.
Furthermore - and even worse - some of the most widely used tests, including those produced by Abbott and Roche Labs and used by Quest Labs and Labcorp, "are designed to detect a subtype of antibodies that doesn’t confer immunity and may wane even faster than the kind that can destroy the virus."
It turns out that there are various kinds of antibodies, and only the antibodies that recognize the spike protein part of the coronavirus can destroy the virus and prevent infection.
The Abbot and Roche tests and other tests that were approved by the Food and Drug Administration and are widely available look for antibodies to a protein in the coronavirus's genetic material. Testing for these non-immunity-producing antibodies produces a "swifter, brighter signal" than testing for the immunity-producing antibodies. Apparently, "manufacturers are not required to prove that the antibodies their tests seek are those that actually confer protection against the virus. Officials at the Food and Drug Administration did not respond to requests for comment on whether the two tests target the appropriate antibodies."
"God, that's crazy," said Angela Rasmussen, a virologist at Columbia University, upon learning that the tests being widely used were not designed to pick up the presence of the important antibody.
Crazy, indeed, like so much else about our national response to this epidemic.