U.S. health regulators cleared for use a booster shot of the Covid-19 vaccine from Pfizer Inc.         PFE,        +1.32%       and BioNTech SE         BNTX,        +5.69%       for children 5 to 11 years, expanding booster access to about 28 million youngsters.

The decision Tuesday by the U.S. Food and Drug Administration permits a third dose of the shot at least five months after the second dose.

It comes weeks after the drugmakers said a third shot safely generated a strong immune response in the children, including significantly increasing antibody levels against the Omicron variant.

“A booster dose can help provide continued protection against Covid-19 in this and older age groups,” said Peter Marks, who heads the FDA’s vaccine division.

Many children now eligible for the shots might not get them, however. Vaccinations among the youths have been relatively low compared with rates in older people. Opinion surveys have found limited support among parents for vaccinating their children, suggesting many of them don’t plan to have their children get a booster.