The announcement means a significant part of the US population – amounting to tens of millions of Americans – are now eligible for a third shot six months after their second.
The decision was expected and came after an independent expert panel convened by the regulatory agency last week voted in favour of recommending the move.
The panel, however, rejected an initial plan by the White House to fully approve Pfizer boosters for everyone aged 16 and over, in what amounted to a rare rebuke of President Joe Biden’s administration.
The group of vaccinologists, infectious disease specialists and epidemiologists concluded that the benefit-risk balance differed for younger people.
Boosters vs global distribution
Pfizer COVID-19 boosters are currently being debated by a separate body of experts convened by the Centers for Disease Control and Prevention (CDC), which may recommend further specifics about recipients.
For example, if obesity is considered as putting a person “at high risk of severe COVID”, that definition would cover more than 42 percent of the US population aged over 20.
The CDC may also have to define which workplaces and other settings might lead to “frequent institutional or occupational exposure to SARS-CoV-2.”
For its part, the FDA indicated this would cover “health care workers, teachers and day care staff, grocery workers and those in homeless shelters or prisons, among others”.
The FDA’s emergency use authorisation (EUA) applies to those aged 18 and up for the high risk of severe disease and high-exposure categories. It also only applies to the Pfizer vaccine.
There has been no decision made on boosters for recipients of the Moderna and Johnson & Johnson vaccines, the only other inoculants authorised for use in the US.
A number of studies have shown two doses of Pfizer or Moderna, or a single shot of J&J, continue to confer high protection against severe outcomes – but this is slightly reduced for the elderly.
The update comes in the midst of an international debate over whether it is ethical for rich countries to provide booster shots when most poor countries remain without widespread access to vaccines to administer even first doses.
The World Health Organization has called for a moratorium on wealthy countries giving out boosters.
The US has argued it is possible to both help middle- and lower-income nations while also protecting its own vulnerable people.
On Wednesday, President Biden announced the US would buy 500 million more doses of the Pfizer vaccine for the world, bringing its total contribution to the global supply to 1.1 billion.