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Adolescents ages 12-15 can now get a booster dose of Pfizer/BioNTech's COVID-19 vaccine (Comirnaty) under emergency use authorization (EUA), the .

The agency also changed the interval for boosters shots of Pfizer's vaccine in all individuals 12 and up to at least 5 months after the second dose (was previously 6 months), and allowed a third dose for certain immunocompromised children ages 5-11 at least 28 days after their two-dose primary series.

This comes about a month after the agency authorized a single-dose booster for teens ages 16 and 17.

"Based on the FDA's assessment of currently available data, a booster dose of the currently authorized vaccines may help provide better protection against both the delta and omicron variants. In particular, the omicron variant appears to be slightly more resistant to the antibody levels produced in response to the primary series doses from the current vaccines," said Peter Marks, MD, PhD, director of the FDA's Center for Biologics Evaluation and Research, in a statement.

FDA cited real-world Israeli data from 6,300 individuals ages 12-15 who received a booster dose at least 5 months after their primary series, and no new safety concerns from a population of 4.1 million individuals in Israel ages 16 and up who have received booster doses.

A benefit/risk analysis found that the risk of vaccine-associated myocarditis was two to three times higher after the second dose than after the third dose among this population, Marks explained during a media briefing.

He added that 98% of the vaccine-associated myocarditis cases were "relatively mild," with a median hospital stay of 1 day and treatment consisting of either non-steroidal anti-inflammatory drugs or acetaminophen.

Marks also shared some additional data on vaccine-associated myocarditis, saying the risk was "somewhat lower" in males ages 12-15 than in those ages 16-30 -- where it occurs in about 1 in 10,000. The "risk seems to peak" in 16- and 17-year-olds, he added.

"The thought here is there is some interaction between the timing of the first two doses being somewhat shorter and the androgenic steroids present in males -- [which] tend to peak in puberty -- that may be leading to this" increased risk, Marks said.

Once again, the agency did not convene the Vaccines and Related Biological Products Advisory Committee (VRBPAC) to support this decision.

When asked why, Marks said that VRBPAC is generally convened "when there is some question that needs public discussion."

"There were 400,000 new cases reported in the U.S., [so] it makes sense to try to move as quickly as we possibly could," he said.

FDA also authorized a third dose of Pfizer's vaccine for children ages 5-11 who underwent solid organ transplant or have another immunocompromising condition and who "may not respond adequately to the two-dose primary vaccination series." Third doses are not authorized for all other children in this age group, the agency noted.

On Tuesday, CDC the 5-month interval for Pfizer boosters and a third dose for certain immunocompromised children.

CDC's Advisory Committee on Immunization Practices (ACIP), which was not convened when the EUA was expanded to 16- and 17-year-olds, will convene on Wednesday, January 5 to discuss booster recommendations for individuals ages 12-15.

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