After Four Months, Pfizer’s COVID Vaccine Still 100% Effective in Adolescents

In March, Pfizer and BioNTech reported that their COVID-19 vaccine demonstrated 100% efficacy in preventing COVID-19 infections among adolescents aged 12 to 15. Longer-term follow-up data now show that the vaccine remains 100% effective against COVID-19 from seven days to over four months after the second dose.

The COVID-19 vaccine has been in use for this age group since May when the Food and Drug Administration (FDA) expanded the scope of its emergency use authorization (EUA).

Now, the vaccine developers intend to submit this new longer-term data to the FDA as part of their application to expand full approval of the vaccine to individuals aged 12 years and older.

But 100% efficacy doesn’t necessarily mean that no vaccinated adolescent will ever get infected, or that boosters will never be recommended.

Does This Translate to 100% Real-World Effectiveness?

“The 100% efficacy is how well the vaccine performs under very controlled conditions when the dose is given at the correct interval and everything is carefully monitored,” Thomas Murray, MD, PhD, Yale Medicine pediatric infectious diseases specialist and associate professor of pediatrics at Yale School of Medicine, told Verywell. “While this number suggests the real work effectiveness will be excellent, it will likely be less than 100%.” 

The clinical trial had a relatively small sample size—2,228 participants—where about half were given the vaccine. All 30 cases of COVID-19 were from the placebo group, exhibiting 100% efficacy.

However, the efficacy measured in clinical trials generally differs from the vaccine effectiveness in real-world settings. The highly controlled environment of a clinical trial doesn't always reflect what happens in everyday circumstances among a larger more varied population.

“Additionally, large numbers of vaccinated [individuals] do mean that inevitably there will be breakthrough cases in some kids,” Michael Storey, PharmD, MS, a medication use strategist at Nationwide Children’s Hospital, told Verywell. “We expect these vaccines will be highly effective in this population, but 100% is just not a reasonable expectation.”

Will Adolescents Need Boosters?

Experts say it’s possible that vaccine efficacy in adolescents will wane over time—similar to vaccination in adults—but more data is needed to know for certain.

“We will need to see a decline in efficacy in this group to say for sure,” Storey said. “It is possible boosters will not be required, or may not be required for several months. We still need clinical data showing that there is a need for and a benefit from boosters in this age group.”

We will continue to learn more about real-world vaccine effectiveness as more adolescents get vaccinated against COVID-19.

“The need for boosters in this age group will depend on whether there are breakthrough infections over time,” Murray said. “Some things that determine this are how long antibody levels remain high after vaccination as well as how well the vaccine works against circulating variants.”

Last Monday, Rochelle P. Walensky, MD, MPH, director of the Centers for Disease Control and Prevention (CDC), strongly encouraged adults to get a booster shot once they are eligible, especially with the emergence of the Omicron variant.

“Many experts do not think there is sufficient evidence that young, healthy people need booster doses and have some concerns about the risk of heart inflammation in young men,” William Moss, MD, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, told Verywell. “However, Omicron may change this risk-benefit calculus if it turns out to be highly transmissible and evades immunity conferred by two doses of an mRNA vaccine.”

At present, the Pfizer-BioNTech COVID-19 vaccine does not yet have full FDA approval for children aged 5 to 15. This recent CDC study shows evidence of sustained effectiveness and long-term safety of the vaccine in 12- to 15-year-olds, which will certainly be considered by the FDA when assessing the data to expand approval, Moss said.

The data doesn’t necessarily mean that the vaccine is more effective among adolescents than in other age groups, and the process for FDA approval remains the same.

“Data showing 100% efficacy is unlikely to make approval faster than any other data showing efficacy is less than 90%,” Storey said. “In either case, the vaccine is highly effective, with a clear favorable risk-benefit profile, so approval should proceed similarly.”

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