Covishield generated higher antibody levels and stronger immune responses than Covaxin, according to a new study that assessed in real-world conditions two years ago the main vaccines used in India against the 2019 coronavirus.

Scientists said the study provides fresh evidence for the superiority of Covishield over Covaxin measured through short-term antibody responses and so-called T-cell immune responses that play a long-term role in curbing symptoms or severe disease in the future.

Immunologists not involved in the study said its findings underscore differences in the immune responses from the two vaccines but cautioned that the results do not imply that Covaxindid not protect people from severe Covid-19.

India has vaccinated nearly a billion people against Covid-19 with Covishield and Covaxin making up more than 98 per cent of the administered doses in 2021 and 2022. Covishield, developed in the UK and produced in India by the Serum Institute of India, uses a genetically engineered adenovirus containing coronavirus proteins to generate immunity against the virus. Covaxin developed by India’s Bharat Biotech contains inactivated or killed coronavirus particles.

Clinical trials before the release of the vaccines had established that both protect people from severe disease but the difference in the vaccines’ platforms had generated debate in scientific circles and among the public on whether one might be superior to the other.

In the study, scientists at the National Centre for Biological Sciences, Bangalore, and 10 collaborating institutions tracked immune responses in 691 volunteers aged between 18 and 45 years from June 2021 to January 2022 before and after they received the vaccines.

They found Covishield elicited higher antibody responses than Covaxin — 98.3 per cent compared with 74.4 per cent in people not exposed to the coronavirus, and 91.7 per cent compared with 66.9 per cent in people who already had antibodies from prior coronavirus exposure.

They also found that Covishield recipients consistently exhibited higher levels of antibodies than Covaxin recipients against the delta and omicron strains of the virus that had fuelled the country’s second and third Covid-19 waves.

“These results will have important implications for future immunisation strategies, at least against Covid-19,” said Satyajit Major, a scientist at the NCBS who led the study published in The Lancet. “The results also tell us that Covaxin didn’t behave as well as it had been promoted.”

“It performed as well as any of the other inactivated virus vaccines produced during the pandemic,” Mayor said. Two Covid-19 vaccines from China and one from Austria are also inactivated vaccines, similar to Covaxin.

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.”

This study, Rath said, provides important information about the immune responses to the two vaccines amid the multiple waves during the pandemic. “We need systematic studies like these to guide future vaccination strategies — ideally, the government should have done such a study.”

Funds for the study came from Hindustan Unilever’s corporate social responsibility initiatives.