A recent study compared the immune responses generated by Covishield and Covaxin, the two main vaccines used in India against the 2019 coronavirus. The study, conducted two years ago under real-world conditions, found that Covishield induced higher levels of antibodies and stronger T-cell immune responses compared to Covaxin.
Although the study highlights differences in immune responses between the two vaccines, it does not imply that Covaxin is ineffective in protecting against severe Covid-19. Both vaccines have been extensively used in India's vaccination campaign, with Covishield and Covaxin constituting over 98% of the administered doses in 2021 and 2022.
Covishield, developed in the UK and manufactured by the Serum Institute of India, utilizes a genetically engineered adenovirus to stimulate immunity against the virus. In contrast, Covaxin, developed by India's Bharat Biotech, contains inactivated coronavirus particles.
The study, conducted by scientists from the National Centre for Biological Sciences and collaborating institutions, tracked immune responses in 691 volunteers aged 18 to 45 who received the vaccines between June 2021 and January 2022. Covishield recipients exhibited higher antibody responses compared to Covaxin recipients, particularly against the delta and omicron variants.
The findings suggest implications for future immunization strategies against Covid-19. However, it's important to note that Covaxin performed similarly to other inactivated virus vaccines produced during the pandemic.
Scientists say the clinical trials and follow-up studies have shown that Covaxin has protected people from severe disease. “We still don’t know how much antibodies are required to protect against disease,” said Satyajit Rath, an immunologist and emeritus faculty at the Indian Institute of Science Education and Research, Pune, who was not associated with the study. “Consequently, lower antibody concentrations do not necessarily imply the vaccine doesn’t protect against severe disease. The evidence shows that all inactivated vaccines protect against severe disease.”