In a new study, Serum Institute of India’s (SII) Covishield has shown 63 per cent overall efficacy rate and 81 per cent efficacy in preventing severe Covid-19 infections in fully vaccinated people. It's one of the first Indian studies conducted to test Covishield’s efficacy during the Delta strain dominated second wave. This preprint study is under submission to The Lancet.


  1. Translational Health Science and Technology, Faridabad along with CSIR- Institute of Genomics and Integrative Biology, National Institute of Immunology and the Indian Consortium of Covid-19 research, worked on this study.
  2. According to the study, the cell mediated immunity, despite the ability of Delta strain to reduce antibody-led immune response.
  3. As the study shows that complete vaccination with Covishield has successfully protected people from severe Covid-19 infection, it encourages people to get both the doses of the vaccine.
  4. However, it added that there was a significant drop in antibody-led immune response to the Delta variant but the cell mediated immunity was maintained in the Covishield vaccine recipients. It also mentions that protection against severe infection is due to cell mediated immunity.
  5. It also mentioned that the T-cell responses were preserved against the recombinant mutant receptors.
  6. The T-cells helped in binding domain antigens to push for cell-mediated immune response to the Delta virus.