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

Summary 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%,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(VE)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 COVID-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.