BNT162b2 booster protects against COVID-19 infection, hospitalization in adolescents

In a national cohort study in Singapore, a booster dose of BNT162b2 maintained individual protection against severe COVID-19 disease among adolescents aged 12–17 years.

 

“[In this patient subgroup], vaccine effectiveness against confirmed SARS-CoV-2 infection after two doses of BNT162b2 decreased over time and increased after a third dose,” said the researchers.

 

Compared with unvaccinated adolescents, vaccine effectiveness following two doses were 66 percent and 25 percent against Delta and Omicron infections, respectively, after adjusting for age, gender, socioeconomic status, ethnicity, and daily infection rate. The effectiveness against Omicron infection jumped to 56 percent following the booster or third dose. [Lancet Infect Dis 2023;23:177-182]

 

“[The lower rate for Omicron vs Delta] is probably due to greater immune evasion by Omicron and is supported by higher incidence of infections observed during the Omicron wave in Singapore compared with the Delta wave,” the researchers noted.

 

This effect was mirrored when evaluating vaccine effectiveness against hospitalization: the rates were 83 percent and 75 percent (against Delta and Omicron, respectively). Following the booster, vaccine effectiveness was 94 percent, as opposed to unvaccinated adolescents.

 

“[These data demonstrate that] vaccine effectiveness against infection for both variants after two doses waned over time, whereas vaccine effectiveness against hospitalization for both variants remained stable, [but] both were increased after three doses,” said the researchers.

 

“[Therefore, our study] showed that a booster dose provided the greatest protection against both infection and hospitalization. Specifically, for Omicron, the booster increased protection against hospitalization to levels similar to those against Delta after the primary series,” they added.

 

However, vaccine effectiveness in the current study was lower than that seen in other trials. [JAMA 2022;327:2210-2219; N Engl J Med 2021;385:2101-2103; MMWR Morb Mortal Wkly Rep 2021;70:1483-1488] This might have been driven by vaccination-differentiated social distancing measures implemented in Singapore from August 10, 2021, the researchers said. “[These measures] restricted access of unvaccinated individuals to settings with potentially higher risk of SARS-CoV-2 transmission … This could have reduced the exposure risk of unvaccinated individuals.”

 

Using comprehensive national data, the researchers evaluated the incidence of confirmed SARS-CoV-2 infection and hospitalization in ~250K adolescents (median age 15 years, 51 percent male) who have received the BNT162b2 vaccine in Singapore from September 1 to December 15, 2021 (Delta wave) and from January 21 to April 28, 2022 (Omicron wave). More than three-quarters (76 percent) of participants were fully vaccinated. About 17 percent were boosted, while 5 percent were unvaccinated.

 

“[Taken together,] these findings highlight the usefulness of the booster dose in reducing stress on healthcare systems and maintaining individual protection against severe disease in an Omicron-dominated wave,” the researchers concluded.

 

Despite the gradual waning of immunity following completion of the primary series for both variants, the findings underscored the ability of the booster to improve vaccine effectiveness. However, the slight waning observed after the booster dose requires further evaluation.