A multi-institutional team of Indian researchers led by the Translational Health Science and Technology Institute (THSTI) evaluated the real-world vaccine effectiveness of Covishield during the SARS-CoV-2 infection surge between April and May, 2021, in India. They also assessed neutralising activity and cellular immune responses against the variants in healthy vaccinated persons to understand the mechanisms of protection.

In the study published in journal “The Lancet Infectious Diseases” which included a comparison between 2379 cases of confirmed SARS-CoV-2 infection and 1981 controls, the vaccine effectiveness against SARS-CoV-2 infection in fully vaccinated individuals was found to be 63%. The vaccine effectiveness of complete vaccination against the moderate-to-severe disease was much higher at 81%. More importantly, the scientists also observed that the Spike-specific T-cell responses were conserved against both the delta variant and wild-type SARS-CoV-2.

Such cellular immune protection might compensate for waning humoral immunity against the virus variants and prevent moderate-to-severe disease and the need for hospitalisation. This study provides comprehensive data on the real-world vaccine effectiveness and immunological response to vaccination which should help guide policy.