▶ Watch Video: Fully vaccinated Americans urged to get boosters as Omicron COVID variant spreads

The Food and Drug Administration has greenlighted a request from Pfizer and BioNTech to allow Americans as young as 16 to get a booster shot of their COVID-19 vaccine, the agency announced on Thursday, clearing a key hurdle before that age group can receive the third shot. Boosters were previously OK’d for ages 18 and up.

“Since we first authorized the 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,” Dr. Peter Marks, the FDA’s top vaccines official, said in a statement.

“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,” said Marks.

As with previous changes to recommendations governing use of the government-purchased vaccines, the Centers for Disease Control and Prevention will also need to weigh in before 16- and 17-year-olds can begin receiving booster shots. Like adults, the teens would be eligible for a booster six months after getting their second dose. 

The FDA’s emergency use authorization comes a little more than a week after Pfizer announced their request, as health authorities are pleading with eligible Americans to seek out the third shot and boost their protection. Beyond a feared surge in breakthrough infections from the Omicron variant, several states are already seeing a wave of Delta variant cases that have strained hospitals.

In a statement, Pfizer’s CEO Albert Bourla praised the decision as “a critical milestone” in responding to the virus. 

“While new variants, including Omicron, emerge across the globe, we believe that the best way to minimize the spread of COVID-19 and any future variants is getting all eligible people fully vaccinated with the first two dose series and a booster dose as recommended,” said Bourla.

Only around 2.6 million Americans aged 16 and 17 years old, or 31%, were fully vaccinated six months ago and will be immediately eligible for another dose, according to the CDC’s data. Today, a little more than half of teens in this age group are fully vaccinated.

Pfizer remains the only COVID-19 vaccine authorized for use in Americans under 18. The company said Wednesday it plans to also submit a renewed request for full approval of the third dose down to 16 years old, citing data from its trial showing the third dose had a 95.6% vaccine efficacy compared to those who did not receive the booster.

Meanwhile, the FDA has yet to greenlight Moderna’s request to authorize its initial two shots for Americans as young as 12. The regulator delayed its decision earlier this year over concerns of the risk of myocarditis, a rare heart inflammation side effect seen after the mRNA vaccines in mostly younger men. 

The FDA and CDC last month also changed their guidance around the mRNA shots, acknowledging data suggesting that the risk of myocarditis could be higher from Moderna’s vaccine than Pfizer’s.

Recent studies continue to show that many cases of myocarditis after vaccination that have occurred “are mild and resolve quickly” after vaccination. Data considered by the CDC’s outside vaccine advisers last month also suggest rates of side effects from the shot, including myocarditis, appear lower after the third dose than the second dose. 

The FDA said on Thursday that “additional real-world data” on climbing COVID-19 cases and the small risk of myocarditis allowed the agency “to reassess the benefits and risks” of using the vaccine in younger recipients.

It is unclear if the CDC’s Advisory Committee on Immunization Practices will be asked to meet again to reconsider their recommendations. Federal supply agreements require vaccinators to wait for the CDC’s updated guidance before rolling out shots, typically after the committee meets to discuss and vote on new recommendations, although governors and local health officials have previously looked for ways to shortcut the process in their states.

Members of the CDC’s panel had voted last month to back softer language suggesting younger adults “may” be allowed to receive a booster shot, citing concerns over the unanswered questions around the safety and need for the extra dose. 

But as cases of the Omicron variant began to spread, the CDC director moved unilaterally last week — without the panel’s input — to strengthen the agency’s recommendations to urge all adults to receive the booster shot. 

More than 20 states have now confirmed at least one case of Omicron. Health officials in multiple states say they believe the variant is currently spreading in their communities, after turning up infections in residents with no ties to international travel. 

Abroad, authorities in the United Kingdom warned late Tuesday that their data on the variant’s growth there suggests Omicron “is likely to outcompete Delta” and could soon dominate cases in the country.

Preliminary data announced by BioNTech and Pfizer on Tuesday suggests fully vaccinated people may need a booster dose in order to gain protection against infection from the highly-mutated strain, though both drugmakers and health officials caution more data will be needed to assess Omicron’s true impact on vaccine effectiveness. 

“The new data, which is very preliminary, and initial data, shows us that the first line of defense with two doses of vaccination might be compromised and three doses of vaccination are required to restore protection,” Özlem Türeci, BioNTech’s chief medical officer, told reporters on Wednesday.