16 and 17-year-olds can get a third dose of Pfizer's COVID-19 vaccine at least six months after completion of their two-shot regimen, the U.S. Food and Drug Administration (FDA) said on Thursday.

The FDA said it had analyzed the immune response data from approximately 200 participants, 18 through 55 years of age, who received a single booster dose approximately six months after their second dose. It noted that the antibody response against the SARS-CoV-2 virus one month after a booster dose of the vaccine, when compared to the response one month after the two-dose primary series in the same individuals, demonstrated a booster response.

"Since we first authorized the (Pfizer-BioNTech) vaccine, new evidence indicates that vaccine effectiveness against COVID-19 is waning after the second dose of the vaccine for all adults and for those in the 16- and 17-year-old age group," said Peter Marks, M.D., Ph.D., director of the FDA's Center for Biologics Evaluation and Research.

"A single booster dose of the vaccine for those vaccinated at least six months prior will help provide continued protection against COVID-19 in this and older age groups," he added.

The U.S. alongside many other countries had already called on its adult population to get booster jabs to pump up immunity that has been found to wane after vaccination.

The calls have recently increased with the emergence of the new Omicron variant, which has already been detected in 60 countries globally.