The US government likely will soon recommend booster shots to people as young as 40 who received either Moderna or Pfizer’s Covid-19 vaccine, according to a source familiar with the plan. 

“I believe it will happen,” the source said.

Last month, the US Food and Drug Administration authorized booster shots for people age 65 and older who received their second shot of Pfizer’s vaccine at least six months ago.

For younger people, the booster is authorized only for certain groups, such as those with certain health conditions or those working in jobs that put them at high risk for contracting Covid-19.

Last week, a panel of FDA advisers recommended that Moderna boosters be given with the same rules. However, boosters for Moderna have yet to be granted authorization by the FDA.

The source said there is “growing concern within the FDA” that US data is beginning to show hospitalizations among people under age 65 who have been fully vaccinated. 

Some more background: If the FDA backs lowering the age for boosters, the plan would then go to the US Centers for Disease Control and Prevention for its sign off. Vaccine advisers to that agency are meeting Thursday to discuss Covid-19 booster shots.

Israel, where nearly all vaccinations have been with Pfizer, started offering boosters in August to everyone more than six months past their second shot, regardless of age.

Israeli researchers told the FDA advisers last week that the boosters have reduced the rate of severe disease in people over age 40.

At that meeting, a senior FDA official said the Israeli data “seems compelling.”

Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, mentioned that newly emerging data in the US “makes us realize that we’re concerned that what was seen in Israel could be seen here." 

“We don’t want to have a wave of severe Covid-19 before we deploy boosters,” he added.

Several members of the advisory committee expressed support for lowering the age recommendation.

“In general, I wasn’t a fan of reducing the cutoff to a lower age, because I think this severe disease isn’t terribly great in that population, but hearing all these arguments I would support that now more,” said Dr. Stanley Perlman, a professor of pediatrics at the University of Iowa.

The advisers voiced concern about giving boosters to younger people, since Pfizer and Moderna’s vaccine have been associated with myocarditis, or inflammation of the heart muscle, in male adolescents and young adults.

Last week, the FDA vaccine advisers recommended that people of all ages who received a Johnson & Johnson vaccine get a booster 2 months after their original shot. Boosters for this vaccine are also awaiting authorization by the FDA.