• Min Kang, Yao Yi, Yan Li, Limei Sun, Aiping Deng, Ting Hu, Jiayi Zhang, Jun Liu, Mingji Cheng, Shen Xie, Min Luo, Jing Jiang, Yawen Jiang, Shixing Tang, and Jianfeng He.
• School of Public Health, Southern Medical University, and Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, China (M.K.).
• Ann. Intern. Med. 2022 Apr 1; 175 (4): 533540533-540.

BackgroundReal-world evidence on inactivated COVID-19 vaccines against the highly transmissible B.1.617.2 (Delta) variant of SARS-CoV-2 is limited, leaving an important gap in the evidence base about inactivated COVID-19 vaccines for use by immunization programs.ObjectiveTo estimate inactivated vaccine effectiveness (VE) against the B.1.617.2 variant.DesignRetrospective cohort study.SettingThe study was based on the first outbreak of the B.1.617.2 variant in mainland China that was discovered and traced in Guangdong in May and June 2021.Participants10 805 adult case patients with laboratory-confirmed infection and close contacts.MeasurementsParticipants were categorized as unvaccinated, partially vaccinated (1 dose), and fully vaccinated (2 doses). We estimated VE against the primary outcome of pneumonia and the secondary outcomes of infections, symptomatic infections, and severe or critical illness associated with the B.1.617.2 variant.ResultsResults are reported in the order of outcome severity. Of 10 805 participants, 1.3% contracted infections, 1.2% developed symptomatic infections, 1.1% had pneumonia, and 0.2% had severe or critical illness. The adjusted VEs of full vaccination were 51.8% (95% CI, 20.3% to 83.2%) against infection, 60.4% (CI, 31.8% to 88.9%) against symptomatic infection, and 78.4% (CI, 56.9% to 99.9%) against pneumonia. Also, full vaccination was 100% (CI, 98.4% to 100.0%) effective against severe or critical illness. By contrast, the adjusted VEs of partial vaccination against infection, symptomatic infection, and pneumonia were 10.7% (CI, -41.2% to 62.6%), 6.8% (CI, -47.4% to 61.0%), and 11.6% (CI, -42.6% to 65.8%), respectively.LimitationObservational study with possible unmeasured confounders; insufficient data to do reliable subgroup analyses by age and vaccine brand.ConclusionFull vaccination with inactivated vaccines is effective against the B.1.617.2 variant. Effort should be made to ensure full vaccination of target populations.Primary Funding SourceNational Natural Science Foundation of China and Key-Area Research and Development Program of Guangdong Province.

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