Effectiveness of inactive COVID-19 vaccines against severe illness in B.1.617.2 (Delta) variant-infected patients in Jiangsu, China

Abstract

The SARS-CoV-2 B.1.617.2 (Delta) variant has caused a new surge in the number of COVID-19 cases. The effectiveness of vaccines against this variant is not fully understood. Using data from a recent large-scale outbreak of COVID-19 in China, we conducted a real-world study to explore the effect of inactivated vaccine immunization on the course of disease in patients infected with Delta variants. We recruited 476 confirmed cases over the age of 18, of which 42 were severe. After adjusting for age, gender, and comorbidities, patients who received two doses of inactivated vaccine (fully vaccinated) had an 88% reduced risk in progressing to the severe stage (adjusted OR: 0.12, 95% CI: 0.02- 0.45). However, this protective effect was not observed in patients who only received only one dose of the vaccine(adjusted OR: 1.11, 95% CI: 0.51- 2.36). The full immunization offered 100% protection from a severe illness among women. The effect of the vaccine was potentially affected by underlying medical conditions (OR: 0.26, 95% CI: 0.03-1.23). This is the largest real-world study confirming the effectiveness of inactive COVID-19 vaccines against severe illness in Delta variant-infected patients in Jiangsu, China.