• Young-Sook Choi, Sukhyun Ryu, Ryu Kyung Kim, Achangwa Chiara, Soojin Baek, Hojin Nam, Eunkyung Park, Eun Kyoung Kim, Young June Choe, Donghyok Kwon, and Won Suk Choi.
• Director for Epidemiological Investigation Analysis, Korea Disease Control and Prevention Agency, Cheongju, Korea.
• J. Korean Med. Sci. 2024 Sep 30; 39 (37): e258e258.

BackgroundThis retrospective observational matched cohort study assessed the differences in critical infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the omicron-predominant period of the coronavirus disease 2019 (COVID-19) pandemic. We evaluated the vaccine effectiveness of bivalent mRNA vaccine compared to unvaccinated individuals.MethodsWe collected COVID-19 case data from the Korean COVID-19 vaccine effectiveness cohort. We calculated the probability of critical COVID-19 cases by comparing the vaccinated and unvaccinated groups.ResultsThe risk of being critically infected due to SAR-CoV-2 infection was 5.96 times higher (95% confidence interval, 5.63-6.38) among older individuals who were unvaccinated compared to those who received the bivalent COVID-19 vaccine.ConclusionOur findings indicate that the bivalent vaccine reduces the disease burden of the SARS-CoV-2 omicron variant, particularly among the older population. Further studies are warranted to determine the effectiveness of booster doses of vaccines for SARS-CoV-2 infection.© 2024 The Korean Academy of Medical Sciences.

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