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

• Published in: The Journal of infectious diseases Vol. 228; no. 3; pp. 261 - 269
• Main Authors: Tang, Lin, Wang, Fu-Zhen, Rodewald, Lance E, Wang, Xuan-Yi, Liu, Si-Yu, Liu, Qian-Qian, Wang, Xiao-Qi, Wu, Dan, Li, Ming-Shuang, Zhang, Qian, Shao, Yi-Ming, Huang, Li-Fang, Song, Yu-Dan, Huang, Yong, Zeng, Xiang, Liu, Li-Jun, Yang, Hong, Huang, Ao-Di, Bao, Li-Ming, Zheng, Hui, Ma, Chao, Lv, Xiao-Ya, Song, Lei, Ma, Zhao, Wang, Shu-Guang, Ma, Hao, Guan, Wei-Jie, Wu, Zhi-Yin, Zhong, Nan-Shan, Yin, Zun-Dong
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 11.08.2023
• Subjects: Adult; Asymptomatic infection; Asymptomatic Infections; Child, Preschool; China - epidemiology; Cohort analysis; Coronaviruses; COVID-19 - prevention & control; COVID-19 Vaccines; Humans; Infections; Major; Pneumonia; Retrospective Studies; Vaccine efficacy; China; vaccine effectiveness; homologous and heterologous booster; inactivated COVID-19 vaccines; China
• ISSN: 0022-1899; 1537-6613; 1537-6613
• DOI: 10.1093/infdis/jiad090

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. China-produced inactivated COVID-19 absolute vaccine effectiveness (VE) levels against Omicron BA.2 infection, pneumonia or worse, and severe COVID-19 were 17%, 66%, and 91%; boosted VEs were 22%, 74%, and 93%. Inactivated vaccines were highly effective against severe COVID-19 in China's then infection-naive population.