Real-world study of Pfizer vaccine in kids finds moderate Omicron protection

A real-world study in Israeli children ages 5 to 11 found that the Pfizer-BioNTech vaccine provided moderate protection against infection and symptomatic diseases, similar to the pattern seen in adults.

Researchers began measuring the impact of the vaccine starting last November, just as the Omicron variant surge was expanding globally. They published their findings yesterday in the New England Journal of Medicine (NEJM).

Similar protection against infection and symptoms

Using data from the country's largest healthcare organization, they included 94,728 vaccinated kids who were matched with unvaccinated controls. To assess vaccine effectiveness, they examined documented infection 14 to 27 days after the first dose, and 7 to 21 days after the second dose.

Over the study period, children were tested after they had contact with an infected person or when they applied for a "green pass", a certificate that allowed vaccinated or recovered people to take part in cultural activities or travel abroad.

The study period ended on Jan 7 of this year, when Israel implemented a new testing policy, which allowed vaccinated people to use rapid tests at home.

After one dose, researchers estimated vaccine effectiveness at 17% (95% confidence interval [CI], 7 to 25), and after two doses, vaccine effectiveness was 51% (95% CI, 39 to 61). They also estimated that the vaccine was 48% effective against symptomatic disease 1 to 3 weeks after the second dose, which they note is lower than the estimated efficacy of 90.7% when the Delta variant was dominant.

They observed that effectiveness may be greater in younger children, those ages 5 and 6, compared to older kids. The estimate was 68% (95% CI, 43 to 84) effective after the second dose.

Given the limitation of the short follow-up period prompted by the testing policy change, the authors said follow-up to assess the impact on severe outcomes such as hospitalization wasn't possible. They wrote that more studies are needed to look at longer-term effectiveness and to explore dose effects in different age groups.

Real-world data useful for guiding policy, but questions remain

In a NEJM audio interview on the study, Lindsey Baden, MD, deputy editor, said the work highlights the speed needed to gain insights into COVID to make better informed clinical and public health decisions.

Eric Rubin, MD, said however that changes in policy, for example, can add challenges to collecting real-world testing over a substantial length of time. He said some of the main findings are that one dose didn't provide much protection and that the second dose only provided moderate protection, which wasn't surprising, given that Omicron was dominant.

"Altogether, I think that these data suggest that the benefits of vaccination are likely to be similar in children as they are in adults, but we are missing important pieces of data," Rubin said.

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