Scientists Endorse Covid Boosters, But to a Point

“People that are vaccinated really are doing very well in terms of hospitalization,” said Michel Nussenzweig, an immunologist at Rockefeller University in New York. Omicron has made it clear that preventing all infections is a lost cause, he added.

If the vaccines prevented infection and spread of the virus, regular boosters might make sense. “But with Omicron, what’s the point?” Dr. Nussenzweig said. “The endgame is keeping people out of the hospital.”

Last fall, Dr. Anthony S. Fauci, the nation’s top pandemic adviser, repeatedly spoke of the importance of preventing symptomatic infections. But in recent days he, too, has been saying that it is hospitalizations that truly matter.

In order to prevent infections, booster shots must be exquisitely timed to a variant’s circulation in the population. Many people who got a third dose early in the fall, for example, were left vulnerable to Omicron because the immune boost had already subsided.

Generally, people are told to get vaccinated against influenza just before the virus starts circulating in winter. If the coronavirus settles into a flulike seasonal pattern, as it seems possible, “you can imagine a scenario where we simply give boosters before the winter each year,” Dr. Hensley said.

Lessons from flu season also suggest that frequent vaccination is unlikely to be helpful. Giving the flu vaccine twice a year “has a diminishing return, and so it may not make sense to do vaccination so frequently,” said Ben Cowling, an epidemiologist at the University of Hong Kong. “For the initial doses that people receive the responses get better and better, but then there’s a turning point.”

“I think it’ll be difficult to get high uptake with more frequent vaccinations,” he added.

Some experts have raised concerns that getting boosters too often — as some people are doing on their own — may even be harmful. In theory, there are two ways in which it could backfire.