Effectiveness of BBV152/Covaxin and AZD1222/Covishield Vaccines Against Severe COVID-19 and B.1.617.2/Delta Variant in India, 2021: A Multi-Centric Hospital-Based Case-Control Study

Background: India introduced BBV152/Covaxin and AZD1222/Covishield vaccines from January 2021. We estimated effectiveness of these vaccines against severe Coronavirus disease 2019 (COVID-19) among individuals aged >=45 years. Methods: We did a multi-centric, hospital-based, case–control study between May and July 2021. Cases were severe COVID-19 patients and controls were COVID-19 negative individuals from 11 hospitals. Vaccine effectiveness (VE) was estimated for full (2 doses ≥14days) and partial (1 dose ≥21 days) vaccination; duration between two vaccine doses and against the Delta variant. We used a random effects logistic regression model to calculate adjusted odds ratios (aOR) with 95% CI after adjusting for relevant known confounders. Findings: We enrolled 1,143 cases and 2,541 controls. The VE of full vaccination was 80% (95% CI: 73%-86%) with AZD1222/Covishield and 69% (95% CI: 54%-79%) with BBV152/Covaxin. The VE was highest for a gap of 6-8 weeks between two doses of AZD1222/Covishield (92%, 95% CI: 82%-96%) and BBV152/Covaxin (92%, 95% CI: 26%-99%). The VE estimates were similar against the Delta strain and sub-lineages. Interpretation: BBV152/Covaxin and AZD1222/Covishield were effective against severe COVID-19 among the Indian population during the period of dominance of highly transmissible Delta variant in second wave of pandemic. An escalation of two-dose coverage with COVID-19 vaccines is critical to control the pandemic in the country. Funding Information: Indian Council of Medical Research Declaration of Interests: None to declare. Ethics Approval Statement: We obtained written informed consent from all the participants or their legally authorized representatives. Study procedures were approved by the Institutional Human Ethics Committees of all participating institutions.