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. 2021 Dec;10(1):1751-1759.
doi: 10.1080/22221751.2021.1969291.

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

Xiao-Ning Li  1 , Yong Huang  1 , Wen Wang  1 , Qin-Long Jing  1 , Chun-Huan Zhang  1 , Peng-Zhe Qin  1 , Wei-Jie Guan  2   3 , Lin Gan  4 , Yi-Lan Li  1 , Wen-Hui Liu  1 , Hang Dong  1 , Yu-Tian Miao  1 , Shu-Jun Fan  1 , Zhou-Bin Zhang  1 , Ding-Mei Zhang  4 , Nan-Shan Zhong  2
Affiliations

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

Xiao-Ning Li et al. Emerg Microbes Infect. 2021 Dec.

Abstract

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%.

Keywords: Coronavirus disease 2019; Delta variant; SARS-CoV-2; efficacy of vaccination; vaccine.

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Conflict of interest statement

No potential conflict of interest was reported by the author(s).

Figures

Figure 1.
Figure 1.
Flowchart of selection of study participants.
Figure 2.
Figure 2.
Effectiveness of the inactivated vaccines against different severity of COVID-19 associated with the Delta variant strain. (A) Effectiveness in the whole population. The abscissa is VE (%) and the ordinate are different severity of clinical manifestations. The bars represent the estimated value of VE. Different colors indicate different vaccination doses. (B) Effectiveness in the study participants aged 18–39 years. (C) Effectiveness in study participants aged 40–59 years. (D) Effectiveness in males. (E) Effectiveness in females.
See this image and copyright information in PMC

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