The United States Food and Drug Administration authorised the use of Pfizer’s COVID-19 vaccine as a booster shot for “certain populations”, which includes people who are at a high risk of getting severe COVID-19 symptoms and those above the age of 65, the authority said in a press release on Wednesday.

The recently approved booster dose will be given to eligible individuals at least six months after they have completed the primary vaccination cycle.

Only Pfizer’s COVID-19 vaccine has been approved for booster inoculation so far by the Food and Drug Administration, the press release said.

Advisers to the Centers for Disease Control and Prevention opened a two-day meeting Wednesday to make their own, more specific recommendations about who should get the extra shots and when, according to reports from Associated Press.

And in their first day of discussions, some experts were so perplexed by the questions surrounding the rationale for boosters that they suggested putting off a decision for a month in hopes of more evidence.

The press release from the Food and Drug Administration suggested the following categories would be eligible for a booster shot of Pfizer’s COVID vaccine:

1) Individuals 65 years of age and older

2) Individuals 18 through 64 years of age at high risk of severe COVID-19

3) Individuals 18 through 64 years of age whose frequent institutional or occupational exposure to SARS-CoV-2 puts them at high risk of serious complications of COVID-19 including severe COVID-19

Janet Woodcock, the acting commissioner of the Food and Drug Administration said, “After considering the totality of the available scientific evidence and the deliberations of our advisory committee of independent, external experts, the FDA amended the EUA (Emergency Use Authorisation) for the Pfizer-BioNTech COVID-19 Vaccine to allow for a booster dose in certain populations such as health care workers, teachers and daycare staff, grocery workers and those in homeless shelters or prisons, among others.”