Effectiveness of inactivated SARS-CoV-2 vaccines against the Delta variant infection in Guangzhou: a test-negative case-control real-world study

• Published in: Emerging microbes & infections Vol. 10; no. 1; pp. 1751 - 1759
• Main Authors: Li, Xiao-Ning, Huang, Yong, Wang, Wen, Jing, Qin-Long, Zhang, Chun-Huan, Qin, Peng-Zhe, Guan, Wei-Jie, Gan, Lin, Li, Yi-Lan, Liu, Wen-Hui, Dong, Hang, Miao, Yu-Tian, Fan, Shu-Jun, Zhang, Zhou-Bin, Zhang, Ding-Mei, Zhong, Nan-Shan
• Format: Journal Article
• Language: English
• Published: London Taylor & Francis 01.01.2021; Taylor & Francis Ltd; Taylor & Francis Group
• Subjects: Coronavirus disease 2019; COVID-19 vaccines; Delta variant; efficacy of vaccination; Immunization; SARS-CoV-2; Severe acute respiratory syndrome coronavirus 2; vaccine; Guangzhou China; China
• ISSN: 2222-1751; 2222-1751
• DOI: 10.1080/22221751.2021.1969291

The effectiveness of inactivated SARS-CoV-2 vaccines against the Delta variant, which has been associated with greater transmissibility and virulence, remains unclear. We conducted a test-negative case-control study to explore the vaccine effectiveness (VE) in real-world settings. We recruited participants aged 18-59 years who consisted of SARS-CoV-2 test-positive cases (n = 74) and test-negative controls (n = 292) during the outbreak of the Delta variant in May 2021 in Guangzhou city, China. Vaccination status was compared to estimate The VE of SARS-CoV-2 inactivated vaccines. A single dose of inactivated SARS-CoV-2 vaccine yielded the VE of only 13.8%. After adjusting for age and sex, the overall VE for two-dose vaccination was 59.0% (95% confidence interval: 16.0% to 81.6%) against coronavirus disease 2019 (COVID-19) and 70.2% (95% confidence interval: 29.6-89.3%) against moderate COVID-19 and 100% against severe COVID-19 which might be overestimated due to the small sample size. The VE of two-dose vaccination against COVID-19 reached 72.5% among participants aged 40-59 years, and was higher in females than in males against COVID-19 and moderate diseases. While single dose vaccination was not sufficiently protective, the two-dose dosing scheme of the inactivated vaccines was effective against the Delta variant infection in real-world settings, with the estimated efficacy exceeding the World Health Organization minimal threshold of 50%.