Effectiveness of inactivated and Ad5-nCoV COVID-19 vaccines against SARS-CoV-2 Omicron BA. 2 variant infection, severe illness, and death

ABSTRACT

BackgroundLimited data are available on effectiveness of inactivated and Ad5-nCoV COVID-19 vaccines in real-world use - especially against Omicron variants in SARS-CoV-2 infection-naive population. During an outbreak in Shanghais SARS-CoV-2 infection-naive population, we evaluated vaccine effectiveness (VE) against Omicron infection, severe or critical COVID-19, and COVID-19-related death. MethodsA matched case-control study was conducted among people aged [≥]3 years between 2 December 2021 through 13 May 2022. Cases were SARS-CoV-2 infected individuals, individuals with severe/critical COVID-19, or COVID-19-related deaths. Controls were selected from consecutively test negative individuals at the same time as cases were diagnosed and were exact-matched on year-of-age, gender, birthplace, illness onset date, and residency district in ratios of 11 with infected individuals and 41 with severe/critical COVID-19 and COVID-19-related deaths. ResultsOur study included 612597 documented SARS-CoV-2 infections, among which 1485 progressed to severe or critical illness and 568 died. Inactivated vaccine was 16.3% (95% CI 15.4%-17.2%) effective against infection, 88.6% (95% CI 85.8%-90.9%) effective against severe/critical COVIID-19 and 91.7% (95% CI 86.9%-94.7%) against COVID-19 death. Ad5-vectored vaccine was 13.2% (95% CI 10.9%-15.5%) effective against infection and 77.9% (95% CI 15.6%-94.2%) effective against severe/critical COVIID-19. Booster vaccination with inactivated vaccines enhanced protection against severe COVID-19 (92.7%, 95% CI 90.1%-94.6%) and COVID-19 death (95.9%, 95% CI 91.4%-98.1%). Inactivated VE against infection began to wane 12 weeks after the last dose but two- and three-dose sustained high protection levels (>80%) against severe/critical illness and death. ConclusionsOur real-world study found high and durable two- and three-dose inactivated VE against Omicron-associated severe/critical illness and death across all age groups, but lower effectiveness against Omicron infection. High direct protection from severe/fatal Omicron COVID-19 provided by inactivated vaccines, and a consequent potential reduction in health-care utilization, reinforces the critical importance of full-series vaccination and timely booster dose administration for all eligible individuals.