Pfizer says its COVID-19 vaccine has 100 percent efficacy in young people

None of the vaccinated 12- to 15-year-olds had symptoms and the shot’s side effects were mild

vial and syringe containing pfizer covid-19 vaccine

Vaccinating kids will be essential to ending the pandemic. Pfizer and BioNTech's COVID-19 vaccine is highly effective in 12- to 15-year-olds, the pharmaceutical company announced March 31.

Asanka Ratnayake/Getty Images

Pfizer and BioNTech’s COVID-19 vaccine proved highly effective in adults. Now it appears to work well in younger people too. 

In a Phase III clinical trial of 12- to 15-year-olds, participants who received the shot developed higher levels of antibodies to the coronavirus on average compared with vaccinated 16- to 25-year-olds from a previous trial (SN: 11/18/20). And those antibody levels make for a vaccine with high efficacy. None of the 1,131 vaccinated teens developed COVID-19 symptoms. There were 18 cases among the 1,129 youths in the unvaccinated group, Pfizer reported in a March 31 news release

That 100 percent efficacy, based on a small number of cases overall, could decrease a bit as the trial continues because additional cases might pop up. Still, the results point to a vaccine that works well in adolescents. 

The news is “astounding and very exciting,” Colleen Kelley, an infectious diseases physician at Emory University in Atlanta who helped lead a trial of Moderna’s COVID-19 vaccine, said in a call with reporters. Though Pfizer has not yet released all the data from the trial, protecting adolescents “will go a long way to end the pandemic,” she said. That’s because kids younger than 12 appear to be less likely than older kids to get infected with the coronavirus and pass it on to others.   

The shot’s side effects in the 12- to 15-year-olds were similar to those seen in the 16- to 25-year-old age group, the company said. The most common side effect in the older participants was pain at the injection site, followed by fatigue and headache.

Pfizer plans to submit the data to the U.S. Food and Drug Administration, as well as the European Medicines Agency, as soon as possible to ask that its emergency use authorizations be altered so that vaccinations can be expanded to those 12 and older.

Last week, Pfizer began testing its vaccine in children ages 6 months to 11 years. Moderna started a trial of its vaccine in similarly aged children last week, and AstraZeneca launched a trial of its vaccine in 6- to 17-year-olds in February.

Infectious disease experts are optimistic that the vaccines could be ready for kids as early as the summer (SN: 2/25/21).

Erin I. Garcia de Jesus is a staff writer at Science News. She holds a Ph.D. in microbiology from the University of Washington and a master’s in science communication from the University of California, Santa Cruz.

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