Real-world effectiveness of original BNT162b2 mRNA COVID-19 against symptomatic Omicron infection among children 5–11 years of age in Brazil: A prospective test-negative design study

Abstract

Objective

To estimate original wild-type BNT162b2 effectiveness against symptomatic Omicron infection among children 5–11 years of age.

Methods

This prospective test-negative, case-control study was conducted in Toledo, southern Brazil, from June 2022 to July 2023. Patients were included if they were aged 5–11 years, sought care for acute respiratory symptoms in the public health system, and were tested for SARS-CoV-2 using reverse transcription polymerase chain reaction. In the primary analysis, we determined the effectiveness of two doses of original wild-type BNT162b2 against symptomatic COVID-19. The reference exposure group was the unvaccinated.

Results

A total of 757 children were enrolled; of these, 461 (25 cases; 436 controls) were included in the primary analysis. Mean age was 7.4 years, 49.7 % were female, 34.6 % were obese, and 14.1 % had chronic pulmonary disease. Omicron accounted for 100 % of all identified SARS-CoV-2 variants with BA.5, BQ.1, and XBB.1 accounting for 35.7 %, 21.4 % and 21.4 %, respectively. The adjusted estimate of two-dose vaccine effectiveness against symptomatic Omicron was 3.1 % (95 % CI, -133.7 % to 61.8 %) after a median time between the second dose and the beginning of COVID-19 symptoms of 192.5 days (interquartile range, 99 to 242 days).

Conclusion

In this study with children 5–11 years of age, a two dose-schedule of original wild-type BNT162b2 was not associated with a significant protection against symptomatic Omicron infection after a median time between the second dose and the beginning of COVID-19 symptoms of 192 days, although the study may have been underpowered to detect a clinically important difference.

Trial registration number

ClinicalTrials.gov number, NCT05403307 (https://classic.clinicaltrials.gov/ct2/show/NCT05403307)