WASHINGTON — The Food and Drug Administration on Thursday expanded eligibility for the updated coronavirus shots to children as young as 6 months old, the latest step to make the retooled doses available to more Americans.
The federal government rolled out the updated boosters from Pfizer-BioNTech and Moderna in September, though the public has shown little interest in the new shots. The government expanded eligibility to children as young as 5 in October.
The new action by the F.D.A. further expands access to the so-called bivalent shots, though there is unlikely to be strong demand for them among parents. Only a small fraction of the country’s youngest children have been immunized since the original vaccines were authorized for that age group nearly six months ago.
The move comes as coronavirus cases in the United States are on the rise. Young children have also been hit hard in recent months by respiratory syncytial virus, known as R.S.V., with cases swamping pediatric units across the United States.
“More children now have the opportunity to update their protection against Covid-19 with a bivalent Covid-19 vaccine, and we encourage parents and caregivers of those eligible to consider doing so — especially as we head into the holidays and winter months where more time will be spent indoors,” Dr. Robert M. Califf, the F.D.A. commissioner, said in a statement.
For the country’s youngest children, eligibility for the updated coronavirus shots will vary depending on which vaccine and how many doses they have received.
Children ages 6 months through 5 years who received Moderna’s two-dose vaccine will be eligible for the company’s updated booster two months after finishing their initial vaccination round.
Pfizer’s vaccine is given as a three-dose series for children ages 6 months to 4 years. For those children, the third dose in the series will now be the updated shot instead of the original formulation.
Young children who have already received all three doses in Pfizer’s series will not yet be eligible for an updated booster. But the F.D.A. said it expected that new data would be available in January concerning the retooled booster for that population, and the agency said it would assess that data “as quickly as possible.”
The broadened eligibility for the updated shots still needs to be signed off on by the Centers for Disease Control and Prevention.
The Biden administration has struggled to generate interest in the updated booster shots, which target both the original version of the virus and Omicron subvariants. Only about 13 percent of Americans ages 5 and up have received one of the new doses so far.
The F.D.A. authorized the Pfizer and Moderna vaccines for the country’s youngest children in June, a move that came a year and a half after the vaccines were first rolled out for adults.
But few young children have been immunized since then. Less than 10 percent of children ages 4 and under have received their first vaccine dose so far, and even fewer have completed their full vaccination round.