1. This national cohort study from Singapore showed a significant reduction in SARS-CoV-2 omicron variant infections in children vaccinated with BNT162b2 as compared to unvaccinated children.
2. Vaccination with BNT162b2 in children is also associated with reduced hospitalization due to SARS-CoV-2 omicron variant infection.
Evidence Rating Level: 1 (Excellent)
Study Rundown: The omicron variant of SARS-CoV-2, first detected in November 2021, disproportionately affects younger populations compared to other known variants. Vaccinations, such as the mRNA vaccine (Pfizer-BioNTech) BNT162b2, have been widely adopted to reduce infections and hospitalizations due to SARS-CoV-2. However, the effectiveness of vaccines in reducing the incidence of omicron infection and hospitalization among children has not been well studied. This national cohort study evaluated the vaccine effectiveness of BNT162b2 for reducing omicron infections and related hospitalizations among children between the ages of five and 11. Anonymized data for the study period of January 21 through April 8, 2022 was collected from administrative records maintained by the Ministry of Health in Singapore. Partial vaccination, defined by one dose of vaccine or up to six days after the second dose, significantly reduced all reported infections, polymerase chain reaction (PCR)-confirmed infections, and hospitalizations, as compared to no vaccination. Full vaccination, defined by seven days or more after the second dose of vaccine, conferred an even greater reduction in omicron infections and hospitalizations. Vaccine effectiveness remained significant after controlling for time after the second dose of vaccine, age groups, and geographic region. As a limitation, long-term efficacy of the vaccines could not be assessed due to the restricted study period.
In-Depth [retrospective cohort]: The present cohort study used records from the Ministry of Health in Singapore to evaluate the efficacy of BNT162b2 (Pfizer-BioNTech) for reducing SARS-CoV-2 omicron variant-related all-cause infections, PCR-confirmed infections, and hospitalizations in children between the age of five and 11. PCR-confirmed infections and hospitalizations serve as proxies for increased severity of illness, as only symptomatic patients are required to undergo additional PCR testing or hospitalization. Data from 255,936 children were collected from January 21 through April 8, 2022. Vaccine effectiveness was determined as one minus the incidence rate ratio, which used the unvaccinated group as the reference group. In total, 67.7%, 12.0%, and 20.3% of the children were fully, partially, and unvaccinated. During the study period, there were 53,429 reported infections, 5,342 PCR-confirmed infections, and 288 hospitalizations. The vaccine effectiveness in partially vaccinated compared to unvaccinated children was 13.6% (95% Confidence Interval [CI], 11.7 to 15.5) against all reported infections, 24.3% (95% CI, 19.5 to 28.9) against PCR-confirmed infections, and 42.3% (95% CI, 24.9 to 55.7) against hospitalizations. The vaccine effectiveness in fully vaccinated compared to unvaccinated children was 36.8% (95% CI, 35.3 to 38.2) against all reported infections, 65.3% (95% CI, 62.0 to 68.3) against PCR-confirmed infections, and 82.7% (95% CI, 74.8 to 88.2) against hospitalizations. Vaccination effectiveness remained significant after accounting for days after second dose, age groups, and geographic region. These findings indicate that there are protective effects of BNT162b2 vaccination against omicron infection and severe illness in children.
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