The US Food and Drug Administration on Monday expanded the emergency use authorization for the Pfizer/BioNTech Covid-19 vaccine boosters for children ages 12 to 15.

The agency also shortened the time needed between an initial series of vaccine and a booster from at least six months after completion of an initial series to at least five months for everyone 12 and older.

Pfizer’s booster dose contains the same amount of the vaccine as the initial doses: 30 micrograms.

Adolescents in this age group became eligible to receive their initial series of the Pfizer/BioNTech Covid-19 vaccine in mid-May, opening vaccinations up to about 17 million additional people.

Now, about half of the populations aged 12 to 15 – about 8.7 million – is fully vaccinated, according to data from the US Centers for Disease Control and Prevention. About 5 million of them have been fully vaccinated for more than five months and are now eligible to receive a booster shot.

Children in this age group represent about 5% of the total US population. They account for about 4% of the fully vaccinated population in the US and about 3% of those eligible to receive a booster shot, according to the latest CDC data.

In October, the CDC recommended that everyone age 16 and up who completed their initial series of the Pfizer/BioNTech or Moderna vaccine at least six months ago receive a booster shot, along with those who received their initial Johnson & Johnson shot at least two months ago. 

The FDA also authorized a third dose as part of the primary series for certain immunocompromised children ages 5 to 11, including those who have received an organ transplant.

Overall, about 68.8 million people are fully vaccinated and boosted against Covid-19. That’s less than half of the nearly 180 million people who are eligible to receive their booster shot and about a fifth of the total US population. And at least 69 million people ages 5 and up have not received their first dose of Covid-19 vaccine, according to the latest CDC data.