Two new observational studies detail Pfizer/BioNTech COVID-19 vaccine protection among US children and adolescents amid the Omicron variant surge, one finding 71% efficacy against infection after a third dose in 12- to 15-year-olds, and the second showing lower risks of infection and hospitalization in vaccinated youth aged 5 to 17 in New York state. The studies were published late last week in JAMA.

Three doses more effective than 2 in teens

In the first study, researchers from the US Centers for Disease Control and Prevention analyzed data from 74,208 drive-thru polymerase chain reaction (PCR) COVID-19 test results from children aged 5 to 11 years, and 47,744 tests from aged 12 to 15 from Dec 26, 2021, to Feb 21, 2022. The tests were conducted by a single pharmacy chain at 6,897 sites in 49 states; Washington, DC; and Puerto Rico.

The researchers compared the effectiveness of two Pfizer COVID-19 vaccine doses at least 2 weeks before testing with no vaccination in children, and two or three doses 2 or more weeks earlier in adolescents. Overall, the study involved 30,888 positive tests and 43,209 negative tests from children aged 5 to 11 and 22,273 positive tests and 25,471 negative tests from 12- to 15-year-olds. Median age was 10 years, 50.2% were girls, 70.1% were White, and 25.7% were Hispanic or Latino.

Among the younger age-group, 78.4% of test results were from unvaccinated children, and 21.3% were from two-dose recipients. In test results from those aged 12 to 15 years, 51.9% were from unvaccinated participants, 46.2% from two-dose recipients, and 1.9% from those who received a third dose.

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