Real-World Effectiveness of Primary Series and Booster Doses of Inactivated Coronavirus Disease 2019 Vaccine Against Omicron BA.2 Variant Infection in China: A Retrospective Cohort Study
Lin Tang, Fuzhen Wang, Lance E. Rodewald, Xuanyi Wang, Siyu Liu, Qianqian Liu, Xiaoqi Wang, Dan Wu, Ming‐Shuang Li, Qian Zhang, Yiming Shao, Li-Fang Huang, Yudan Song, Yong Huang, Xiang Zeng, Lijun Liu, Hong Yang, Aodi Huang, Liming Bao, Hui Zheng, Chao Ma, Xiao-Ya Lv, Lei Song, Zhao Ma, Shuguang Wang, Hao Ma, Wei‐jie Guan, Zhiyin Wu, Nanshan Zhong, Zundong Yin
Abstract
BACKGROUND: China has been using inactivated coronavirus disease 2019 (COVID-19) vaccines as primary series and booster doses to protect the population from severe to fatal COVID-19. We evaluated primary and booster vaccine effectiveness (VE) against Omicron BA.2 infection outcomes. METHODS: This was a 13-province retrospective cohort study of quarantined close contacts of BA.2-infected individuals. Outcomes were BA.2 infection, COVID-19 pneumonia or worse, and severe/critical COVID-19. Absolute VE was estimated by comparison with an unvaccinated group. RESULTS: There were 289 427 close contacts ≥3 years old exposed to Omicron BA.2 cases; 31 831 turned nucleic acid amplification test-positive during quarantine, 97.2% with mild or asymptomatic infection, 2.6% with COVID-19 pneumonia, and 0.15% with severe/critical COVID-19. None died. Adjusted VE (aVE) against any infection was 17% for primary series and 22% when boosted. Primary series aVE in adults >18 years was 66% against COVID-19 pneumonia or worse and 91% against severe/critical COVID-19. Booster dose aVE was 74% against pneumonia or worse, and 93% against severe/critical COVID-19. CONCLUSIONS: Inactivated COVID-19 vaccines provided modest protection from infection, very good protection against pneumonia, and excellent protection against severe/critical COVID-19. Booster doses are necessary to provide strongest protection.