Pfizer-BioNTech COVID-19 vaccine more than 90% effective in teens, study finds

March 3 (UPI) -- The Pfizer-BioNTech COVID-19 vaccine is 91% effective at protecting young people ages 12 to 18 years against infection for at least four months after their second shot, a study published Thursday by JAMA Network Open found.

The two-dose vaccine is also 85% effective in this age group at preventing symptomatic illness from the virus for the same period, the data showed.

Of the three COVID-19 vaccines approved for use in the United States -- shots from Johnson & Johnson and Moderna are the others -- the Pfizer-BioNTech product is the only one cleared for people age 18 years and younger.

Those ages 12 to 17 years receive the same vaccine dose as adults, while children age 12 years and younger receive one that is about one-third of that amount, according to the Food and Drug Administration.

"We found that the ... vaccine was effective at preventing ... infections in adolescents aged 12 to18 years," researchers, from Yale University in New Haven, Conn., wrote.

"Prevention of asymptomatic infection is particularly important in adolescents because they are more likely than adults to be asymptomatic when infected and may be more likely to unknowingly spread the infection to others," they said.

Earlier reports from the Centers for Disease Control and Prevention also indicated that the Pfizer-BioNTech vaccines is more than 90% effective at preventing serious illness from the virus in that age group.

However, agency data also suggests that the shot may be less effective in younger children.

In January, the FDA approved booster doses of the vaccine for those 12 to 17.

Still, concern has existed about heart-related side effects with the vaccine in this age group, though they are rare and could be mitigated by a dose adjustment, research suggests.

For this study, the Yale University researchers analyzed data on more than 500 youngsters age 12 to 17 for COVID-19 between June 1 and Aug. 15 last year, when the virus' Delta variant was the most common one in circulation.

Among the participants, about 25% were fully vaccinated, meaning they had received both doses of the Pfizer-BioNTech shot, the researchers said.

Of the participants who tested positive for COVID-19, 93% were unvaccinated, the data showed.

More than 60% of the unvaccinated participants infected with the virus developed symptoms, and nine of them required hospital care, the researchers said.

Of the 10 fully vaccinated participants infected with the virus, none required hospital care, according to the researchers.

"The estimated effectiveness was high even against cases with the Delta variant," the researchers wrote.