The New York Times had an excellent article on October 27 discussing the role of B lymphocytes–which produce antibodies to viruses and other invading pathogens–and T lymphocytes–some of which directly attack and destroy the pathogens, and others of which develop memory for components of the invading pathogens.
After a person’s immune system has defeated an infection by COVID-19 or any other virus, that person’s B cells continue producing antibodies to that virus but, over time, antibody production and antibody levels gradually tail off. But as University of Pennsylvania immunologist Scott Hensley states in the Times article:
Declining antibody levels after the acute infection has resolved “is the sign of a normal healthy immune response,” Dr. Hensley said. “It doesn’t mean that those people no longer have antibodies. It doesn’t mean that they don’t have protection.”
Dr. Hensley says recent hyperventilating headlines about a study from Imperial College London that demonstrates a gradual decline in antibody levels post‐COVID infection are “silly.”
That’s because B cells and antibody production are only one component of the immune response. Dr. Paul Elliott, an epidemiologist at Imperial College London points out in the Times article that some T lymphocytes retain memory of the pathogen and stimulate B cells to pump out more antibodies to it, if and when the pathogen re‐invades. Other T lymphocytes directly attack and destroy the pathogen they remember. Still other T cells release factors that mobilize other components of the host’s immune system against the pathogen.
The Times article quotes Dr. Shane Crotty, a virologist at the La Jolla Institute for Immunology as saying:
A very small number of people may not make any antibodies. But even those people may have immune cells called T cells that can identify and destroy the virus. The vast majority of people infected with the coronavirus develop lasting cellular responses, according to several recent studies.
T cells are unlikely to prevent infection, but they may at least prevent serious illness by blunting the attack, Dr. Crotty said. Given all that, he said, interpreting low antibody levels to mean that immunity disappears, or that coronavirus vaccines will not be effective is “wrong.”
In the October 24 Cato Daily Podcast, I discussed, among other things, how T cell immunity might mean that many more people than we realize are already immune to COVID-19. T cell memory of other coronaviruses, e.g., those that cause the common cold, might also confer “partial immunity” to people exposed to COVID-19, and this might help explain why some people get milder symptoms—or no symptoms at all—from COVID-19 infections.
By educating readers who might otherwise conclude that reports of waning antibody levels in post‐COVID‐19 patients is ominous news, New York Times science reporter Apoorva Mandavilli provided a public service.