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

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
• SARS-CoV-2
• efficacy of vaccination
• Delta variant
• vaccine

Ethics statement

All data, including demographic information and vaccination information, are collected on the basis of measures to block community transmission. Personal information is not involved in this article.

Acknowledgements

We thank the assistance offered by funders and each cooperative institution, and we are deeply grateful to every medical staff who helped collect data in this epidemic.

Disclosure statement

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

Additional information

Funding

This work was supported by The Key Project of Medicine Discipline of Guangzhou [grant number 2021-2023-11]; The Basic Research Project of Key Laboratory of Guangzhou [grant number 202102100001]; Foshan Scientific and Technological Key Project for COVID-19 [grant number 2020001000430]; Zhuhai Scientific and Technological Key Project for COVID-19 [grant number ZH22036302200008PWC]; COVID-19 Vaccines Scientific Research Project of the China National Key R&D Programme “Post-marketing Research on Immunity Persistence and Effectiveness of Inactivated COVID-19 Vaccine” [grant number 2021YFC0863900]; The Health Science and Technology Project of Guangzhou “Research on immunization Strategy of SARS-CoV-2 vaccines” [grant number 20211A011051].