Real-world Effectiveness of a COVID-19 Vaccine (BNT162b2) against SARS-CoV-2 Infection during the Omicron Variant Predominant Period among Thai Adolescents

Abstract

This study assessed the real-world vaccine effectiveness (RVE) of a 2-dose schedule of BNT162b2 against the Omicron variant among Thai adolescents aged 12 to 18 in the Eastern Region. A test-negative matched 1:1 case-control design was conducted using nationwide records of RT-PCR tests and vaccination history. Cases were matched with controls by the specimen collection date and residential province. Conditional logistic regression was used to determine the RVE. From January to June 2022, when Omicron prevailed, 7,770 adolescents (3,758 detected and 4,012 undetected) were reported to the system. At the time of the RT-PCR test, 684 (14%), 295 (6%), 3,834 (78%), 104 (2%), and three adolescents had received no, one, two, three, and four doses of any COVID-19 vaccines, respectively. A total of 3,304 eligible adolescents with 2-dose of BNT162b2 with a median (interquartile range (IQR)) age of 16 (14–17) years were analyzed. The median (IQR) interval from the last vaccination to RT-PCR test was 91 (55–125) days. The age-adjusted RVE of BNT162b2 against infection was 22% (95% confidence interval (CI) 5–35%). The highest RVE was 71% (95% CI -9–92%), which occurred 15–29 days after vaccination. We therefore recommend that a booster dose be considered.

Keywords: COVID-19 vaccine, adolescent, Omicron, SARS-CoV-2, vaccine effectiveness