Should I get a fourth shot now, or wait for an Omicron-specific booster?

On Aug. 15, Britain became the first country to authorize a booster vaccine designed to target the Omicron variant in addition to the original coronavirus. The new vaccine is bivalent, meaning it will combat two variants of the virus.

A similar booster is likely coming to the U.S. in the fall. (The shot that Britain approved is meant to protect against the first strain of Omicron, which sent cases surging this past winter, while the U.S. is waiting on a vaccine that can specifically target BA.5, the version of the virus that is currently dominant.) The Biden administration expects to roll out these retooled vaccines in September, although it is unclear exactly when Pfizer and Moderna, the companies producing the vaccines, will make them available; when the Food and Drug Administration will authorize them; and which populations will be cleared to receive them first. The new boosters may roll out first to groups that are at higher risk of severe outcomes from Covid, such as older and immunocompromised people, before being made available to others.

With that new booster shot on the horizon, doctors and infectious disease experts said they were fielding questions as to whether people should get a fourth shot now or wait for the Omicron-specific booster.

If you are eligible for a fourth shot:

The C.D.C. recommends that people receive booster shots as soon as they become eligible. Currently, all adults who are 50 or older, and people who are 12 and older and are immunocompromised can receive a fourth shot.

Experts agreed that those who qualified for the booster shot now should get it. The older you are, the more important it is to get a fourth shot, said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco.

In general, if you have not received a vaccine or recovered from a Covid infection in the past six months, “getting a booster is a good idea,” said Shane Crotty, a virologist at the La Jolla Institute for Immunology.

If you are not yet eligible for a fourth shot:

Despite the C.D.C.’s recommendations, experts acknowledged that people who are not technically eligible for a fourth shot are getting them. Some have timed their second boosters to strategically “top up” their antibodies, Dr. Chin-Hong said, scheduling shots before a wedding or a trip abroad.

However, experts said, if you are under 50 and do not have underlying health conditions, and you have already received one booster shot previously, you can wait for the Omicron-specific booster shot.

People with “hybrid immunity” — those who have received a booster shot in the past and recovered from a Covid infection — should also consider waiting for the Omicron-specific shot, said Dr. Paul Sax, an infectious disease expert at Brigham and Women’s Hospital and a professor at Harvard Medical School. Unless someone is immunocompromised or elderly, “it doesn’t make a whole lot of sense for them to run out and get another vaccine now,” he said.

Aubree Gordon, an epidemiologist at the University of Michigan, said the general recommendation was for people to wait five months between booster doses. While the Covid vaccines are safe and effective, back-to-back booster shots are unlikely to add much benefit.

“If you get a booster now and you get another booster Sept. 15, don’t expect that second shot to do anything,” Dr. Crotty said.

While the anticipated Omicron-specific shot will offer better protection against the variant currently circulating in the United States, it won’t guarantee protection from infections.

“Boosters against Omicron are not going to be a magic shield,” Dr. Crotty said. But experts agree that any Covid vaccine you get — the booster available now or an Omicron booster in the fall — is meant to prevent severe disease. So far, all Covid vaccines have been extremely effective in preventing hospitalizations and death.