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(The Hill) — The Food and Drug Administration on Monday authorized Pfizer booster shots for people aged 12 to 15 years, another expansion in the population eligible for the third shots.

Booster shots are seen as a key tool to fight the omicron variant, which has shown a heightened ability to infect people who have two shots, though vaccinated people still have important protection against severe disease.

The FDA also shortened the time for all adults to get their booster shots, down to five months from six months after the initial shots.

Finally, for children 5-11 years old, the FDA authorized a third shot for certain immunocompromised children, who it said might not respond fully to two shots.

“Based on the FDA’s assessment of currently available data, a booster dose of the currently authorized vaccines may help provide better protection against both the delta and omicron variants. In particular, the omicron variant appears to be slightly more resistant to the antibody levels produced in response to the primary series doses from the current vaccines,” said Peter Marks, a top FDA vaccine official.

“With this in mind, the FDA has extended the range of individuals eligible to receive a booster, shortened the length of time between the completion of the Pfizer primary series for individuals to receive a booster and is authorizing a third protective vaccine dose for some of our youngest and most vulnerable individuals,” he added.

The FDA said the decision on boosters for 12-15 year-olds was based on real-world data from 6,300 people in Israel.

“These additional data enabled the FDA to reassess the benefits and risks of the use of a booster in the younger adolescent population in the setting of the current surge in COVID-19 cases,” the agency said. “The data shows there are no new safety concerns following a booster in this population.”

The FDA said there were no new cases of myocarditis in that group from Israel, referring to heart inflammation that officials have been monitoring as a rare vaccine side effect, particularly in younger people.