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).
