Relative vaccine effectiveness against Delta and Omicron COVID-19 after homologous inactivated vaccine boosting: a retrospective cohort study. Issue 11 (11th November 2022)

• Record Type: Journal Article
• Authors: Tang, Lin; Zhang, Yanyang; Wang, Fuzhen; Wu, Dan; Qian, Zhao-Hui; Zhang, Rui; Wang, Ai-Bin; Huang, Chang; Wang, Haifeng; Ye, Ying; Lu, Mingxia; Wang, Changshuang; Ma, Ya-Ting; Pan, Jingjing; Li, Ya-fei; Lv, Xiao-Ya; An, Zhijie; Rodewald, Lance; Wang, Xuan-Yi; Shao, Yi-Ming; Wu, Zhi-Yin; Yin, Zundong
• Is Part Of: BMJ open. Volume 12:Issue 11(2022)
• Publication Date: 2022-11-11
• Subjects: COVID-19 -- Epidemiology -- Immunology; Medicine -- Research -- Periodicals; 610.72
• DOI: 10.1136/bmjopen-2022-063919
• Languages: English
• ISSNs: 2044-6055

Abstract

Objective: Two COVID-19 outbreaks occurred in Henan province in early 2022—one was a Delta variant outbreak and the other was an Omicron variant outbreak. COVID-19 vaccines used at the time of the outbreak were inactivated, 91.8%; protein subunit, 7.5%; and adenovirus5-vectored, 0.7% vaccines. The outbreaks provided an opportunity to evaluate variant-specific breakthrough infection rates and relative protective effectiveness of homologous inactivated COVID-19 vaccine booster doses against symptomatic infection and pneumonia. Design: Retrospective cohort study Methods: We evaluated relative vaccine effectiveness (rVE) with a retrospective cohort study of close contacts of infected individuals using a time-dependent Cox regression model. Demographic and epidemiologic data were obtained from the local Centers for Disease Control and Prevention; clinical and laboratory data were obtained from COVID-19-designated hospitals. Vaccination histories were obtained from the national COVID-19 vaccination dataset. All data were linked by national identification number. Results: Among 784 SARS-CoV-2 infections, 379 (48.3%) were caused by Delta and 405 (51.7%) were caused by Omicron, with breakthrough rates of 9.9% and 17.8%, respectively. Breakthrough rates among boosted individuals were 8.1% and 4.9%. Compared with subjects who received primary vaccination series ≥180 days before infection, Cox regression modelling showed that homologous inactivated booster vaccination was statistically significantly associated with protection from symptomatic infection caused by Omicron (rVE 59%; 95% CI 13% to 80%) and pneumonia caused by Delta (rVE 62%; 95% CI 34% to 77%) and Omicron (rVE 87%; 95% CI 3% to 98%). Conclusions: COVID-19 vaccination in China provided good protection against symptomatic COVID-19 and COVID-19 pneumonia caused by Delta and Omicron variants. Protection declined 6 months after primary series vaccination but was restored by homologous inactivated booster doses given 6 months after the primary series.