The United States is expanding its COVID-19 booster because it faces a surge in omicrons, and the Food and Drug Administration allows additional Pfizer injections for children as young as 12 years old.

Boosters have been recommended to everyone 16 years of age and older, and federal regulators decided on Monday that once enough time has passed since the last injection, people aged 12 to 15 can also use boosters.

But as the course restarts after the holidays, this move is not the last step. The Centers for Disease Control and Prevention must decide whether to recommend boosters for young teenagers. The director of the CDC, Dr. Rochelle Walensky, is expected to take office later this week.

The FDA also stated that every person 12 years of age and older who is eligible for a booster can get a dose as early as five months after the last injection instead of six months.

The vaccine can still provide strong protection against any type of serious illness caused by COVID-19. But health authorities urge all people who are eligible for the booster dose to have the best chance of avoiding the milder breakthrough infection from the highly contagious omicron mutant.

Compared with adults, children often suffer from COVID-19 at a milder rate. But in the omicron wave, children’s hospitalization rates are on the rise—most of them are not vaccinated.

The vaccine produced by Pfizer and its partner BioNTech is the only choice for children of any age in the United States. According to data from the Centers for Disease Control and Prevention, approximately 13.5 million people between the ages of 12 and 17-just over half of this age group-received two Pfizer injections.

For families who want to protect their children as much as possible, the booster age limit causes problems.

Older teenagers aged 16 and 17 are eligible for boosters in early December. But the initial vaccination was opened in May for teenagers between 12 and 15 years of age. This means that those who ranked first in the spring may be millions of people. Compared with older teenagers, the last time they took their medicine was about a few months.

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As for younger children, a pediatric dose for children aged 5 to 11 was recently introduced in November-experts say that healthy young people should be protected for a period of time after the second injection. But the FDA also said on Monday that if young children have a severely weakened immune system, they will receive a third vaccination 28 days after the second vaccination. This is the same time as the third dose that has been recommended for immunocompromised adolescents and adults.

Pfizer is studying its vaccine for children under 5 years of age, in even smaller doses.