People 50 and older can soon get a second COVID-19 booster dose. But is it needed?

A second round of COVID-19 booster shots is expected to be approved for people 50 and older as soon as this week, coming about four months after federal authorities said all Americans were eligible for the first booster shot.

This time, though, the Food and Drug Administration is not expected to recommend the shots, the New York Times reported. It likely will simply say people in that age range who want them can receive them.

» READ MORE: The FDA is expected to clear an additional COVID-19 booster shot

Here’s what you need to know about this next stage in the vaccination process:

Moderna has petitioned the FDA to approve a fourth round of its vaccine for all adults, and Pfizer has done the same for adults 65 and older. Approval of those doses for people 50 and older is expected to come this week, the Times has reported, but the Centers for Disease Control and Prevention would also have to offer its recommendations before shots start going into arms.

Experts believe the omicron subvariant BA.2, currently causing a case surge in Europe, will soon do the same in the United States. How serious that surge will be is uncertain, though. The huge number of Americans who caught omicron, about 24 million, according to the CDC, likely have significant protection against the variant that should allow most to avoid anything worse than mild symptoms. That, along with the protection against serious illness and death the existing series of vaccines still offer, could keep cases and hospitalizations from spiking significantly.

» READ MORE: Is the latest COVID-19 surge in Europe coming to the U.S.?

As omicron showed, though, even less potent forms of COVID can still kill thousands and put many more in the hospital. Older people generally have less robust immune systems, and a booster shot for them soon would improve their ability to cope with another surge in the near future.

The United States has only made second boosters after the initial series of two shots available to people with compromised immune systems. But Israel offered the fourth round of shots to older people and health-care workers earlier this year. An Israeli study in the New England Journal of Medicine this month showed antibody concentration increased by a factor of nine to 10, slightly better than the antibody response shortly after third shots. Another Israeli preprint published March 24 found just 0.03% of people ages 60 to 100 who received a second booster died of COVID within 40 days of receiving that shot, compared to 0.1% of people in the same age range who had received three doses.

A January study that has not been peer reviewed found 12 days after subjects 60 and older received a fourth dose their rates of COVID infection were two times lower than among people who had three doses, and rates of severe illness were four times lower.

Those robust antibody responses fade in the months after vaccination, but if a case surge is around the corner, now may be the time for more vulnerable older Americans to get another dose.

“To me, potential benefits of 2nd booster are large (esp. w/ new surge coming), risks=near-zero, so why not give folks the option?” tweeted Bob Wachter, chair of the department of medicine at University of California, San Francisco.

Scientists emphasize that the protection against serious illness and death is already quite high after three shots of the Pfizer or Moderna vaccines.

It isn’t clear how much benefit most people would receive from another dose. There’s little doubt another booster shot would help keep some people from catching COVID at all, though even that isn’t guaranteed. That New England Journal of Medicine study found fourth doses were “somewhat efficacious” at preventing symptomatic illness.

If the goal of vaccination in America is to continually prevent even mild COVID infections, that will likely require an unsustainable regimen of doses, Rochelle Walensky, the CDC’s director, said in an interview with The Inquirer last week.

If the intention of vaccination is rather to focus on preventing serious illness, hospitalizations, and deaths, most people — some 66% of Americans are fully vaccinated, meaning they’ve had their initial shots — may have all the protection they need for the time being. Paul Offit, pediatrician and director of the Vaccine Education Center at Children’s Hospital of Philadelphia, questioned the results of the Israeli study, saying it didn’t include information on the underlying health conditions of the older people who got a fourth dose. If an older person is healthy, he said, it wasn’t clear how much more benefit they would get from a second booster.

“I’d like to see the data,” he said. “I’m over 70, and I’m in no rush to get a fourth dose.”

Offit has been skeptical of booster shots, saying the original series of vaccines offers long-term protection against hospitalization and death for most people.

» READ MORE: Here’s why some people are getting COVID-19 shots now

The downside of a fourth shot is mostly the postvaccination side effects people have been experiencing since the vaccine rollout began, according to a preprint of an Israeli study on people who received fourth doses. Typically, that’s no worse than flulike conditions for a day or so.

Offit, though, said for some older people, those side effects may be enough of a reason to avoid a fourth dose. He also raised a concern of “original antigenic sin,” that too much exposure to one kind of vaccine may make people less likely to benefit from improved iterations of that vaccine. It might matter, he said, if pharmaceutical companies soon develop new generations of vaccine designed to be more effective against COVID variants. But this idea has not been tested in clinical trials.

There’s no risk of additional shots “wearing out” the immune system, health experts have said. There is the possibility, though, that the immune system can reach a maximum level of response to vaccines. Third doses of Pfizer or Moderna vaccines prompted a significantly better immune response than what happened after second doses, but the immune response after fourth doses was only a little better than what was seen after a third.

Offit is on an FDA panel that reviews COVID vaccines, but it was not consulted on the question of another round of boosters for older people. The panel will meet April 6, he said, to discuss whether another round of boosters should be made available to all Americans.