Effectiveness of Inactivated COVID-19 Vaccines Against Symptomatic, Pneumonia, and Severe Disease Caused by the Delta Variant: Real World Study and Evidence - China, 2021

What is already known about this topic? Effectiveness of China's 2 inactivated vaccines (BBIBPCorV and CoronaVac) against pre-Delta severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) variants ranged from 47% to over 90%a, depending on the clinical endpoint, and with greater effectiveness against more severe coronavirus disease 2019 (COVID-19). During an outbreak in Guangdong, inactivated vaccine effectiveness WE) against the Delta variant was 70% for symptomatic infection and 100% for severe COVID-19. However, separate or combined VE estimates for the two inactivated vaccines against Delta are not available. What is added by this report? In an outbreak that started in a hospital, VEs of completed primary vaccination with inactivated COVID-19 vaccines against symptomatic COVID-19, COVID-19 pneumonia, and severe COVID-19 caused by the Delta variant were 51%, 61%, and 82%. Completed primary vaccination reduced the risk of progressing from mild to moderate or severe COVID-19 by 74%. VE estimates for BBIBP-CorV and CoronaVac or combined vaccination were similar, and partial vaccination was ineffective. What are the implications for public health practice? Completed primary vaccination with either of the 2 inactivated GOVID-19 vaccines reduces risk of symptomatic COVID-19, COVID-19 pneumonia, and severe COVID-19 caused by the Delta variant. Completion of the completed primary vaccination with two doses is necessary for protection from Delta.