Pfizer vaccine effectiveness against Omicron in children aged 5-11 years.

The Omicron variant of SARS‐CoV‐2 was first identified in November 2021 and has rapidly replaced delta as the dominant variant in many countries. There are few data on vaccine effectiveness in primary school‐aged children. A study analysed data on 255 936 children in Singapore aged 5–11 years with SARS‐CoV‐2 infection diagnosed by polymerase chain reaction (PCR) and/or rapid antigen testing. Data were collected on COVID‐19‐related hospitalisations of unvaccinated, partially vaccinated (≥1 day after the first dose of the Pfizer BNT162b2 mRNA vaccine and ≤6 days after the second dose), and fully vaccinated children (≥7 days after the second dose). Vaccine effectiveness was calculated from the incidence rate ratio of outcomes using Poisson regression. In unvaccinated children, the incidence of reported SARS‐CoV‐2 infection was 3303.5 per million person‐days, of PCR‐confirmed SARS‐CoV‐2 infection was 473.8 per million, and of COVID‐19 related hospitalisation was 30.0 per million person‐days. For partially vaccinated children, vaccine effectiveness against all SARS‐CoV‐2 infections was 13.6% (95% confidence interval (CI), 11.7–15.5), against PCR‐confirmed SARS‐CoV‐2 infection was 24.3% (95% CI, 19.5–28.9), and against COVID‐19 related hospitalisation was 42.3% (95% CI, 24.9–55.7). For fully vaccinated children, vaccine effectiveness was 36.8% (95% CI, 35.3–38.2), 65.3% (95% CI, 62.0–68.3) and 82.7% (95% CI, 74.8–88.2), respectively.