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Pfizer's COVID-19 vaccine was safe and effective in adolescents, with non-inferior immunogenicity compared with a sample of younger adults, according to the first data on the vaccine in this population published in a peer-reviewed journal.

Among adolescents ages 12 to 15 without evidence of prior SARS-CoV-2 infection, observed vaccine efficacy was 100% at 7 days following the second dose (95% CI 75.3%-100%), with 16 cases in the placebo group and zero in the vaccine group, reported Alejandra Gurtman, MD, of Pfizer in Pearl River, New York, and colleagues.

Moreover, the safety profile was similar to that seen in younger adults, with participants reporting transient mild to moderate reactogenicity, including injection site pain, fatigue, and headache, the authors wrote in the

Immunogenicity was non-inferior among the adolescents compared with a sample of individuals ages 16 to 25, the team added.

The company previously shared top-line numbers via press release in March, but said the plan was to submit the data to a peer-reviewed journal. The FDA expanded the scope of emergency use authorization for Pfizer's COVID-19 vaccine to include adolescents as young as age 12 earlier this month.

The phase III trial consisted of 2,264 adolescents ages 12 to 15 who were healthy or had stable preexisting disease, including HIV and hepatitis B or C. They were assigned 1:1 to receive either 30 μg of vaccine or saline placebo, 21 days apart. After vaccination, participants were instructed to keep a symptom diary for 7 days following each dose.

From Oct. 15, 2020 to Jan. 12, 2021, there were 1,131 participants who received vaccine and 1,129 who received placebo. A little over half the participants were boys, and 86% were white. Some participants (5%) had evidence of prior SARS-CoV-2 infection, and were excluded from the primary analysis (n=1,983). However, when they were factored in, vaccine efficacy was still 100% (95% CI 78.1%-100%), with 18 cases in the placebo group and zero in the vaccine group.

After the first dose, there were three cases of COVID-19 within 11 days in the vaccine group compared with 12 in the placebo group, for a vaccine efficacy of 75%, albeit with wide confidence intervals (95% CI 7.6%-95.5%).

Examining safety, the authors compared a subset of adolescents ages 12 to 15 with individuals ages 16 to 25. Headache and fatigue were the most common systemic adverse events, with a lower proportion of adolescents reporting severe headache or severe fatigue than the older group. Slightly more adolescents than young adults reported a fever after the second dose (20% vs 17%, respectively) and use of antipyretic agents (37% vs 32%).

Fewer severe adverse events were reported in adolescents than in young adults (0.6% vs 1.7%, respectively), though a higher proportion reported lymphadenopathy (0.8% vs 0.2%). There were no thromboses, hypersensitivity adverse events, or vaccine-related anaphylaxis, and none of the severe adverse events were judged to be related to the vaccine. There were no deaths.

Limitations noted by the authors included the lack of racial and ethnic diversity in the adolescent cohort, though they added that all adolescents ages 12 to 15 were from the U.S., whereas individuals ages 16 to 25 were recruited globally. The researchers said they could not examine the effects of other adolescent vaccines on COVID-19 vaccination, nor did they determine whether this vaccine prevents asymptomatic infection or transmission of the virus in this population.

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