Bharat Biotech’s coronavirus vaccine, Covaxin, has shown long-term antibody and T-cell memory responses three months after the shot was administered to phase 1 trial volunteers, PTI reported, citing a research paper published by the Hyderabad-based firm. The results, however, have not been peer-reviewed yet.

T-cells, a type of white blood cell that makes up part of a healthy immune system, are thought to be essential to protect against infection from the SARS-CoV-2, and could provide longer immunity than antibodies. Bharat Biotech said that its indigenous vaccine may persist for six to 12 months. It added that in Phase 2 trials the vaccine was well-tolerated with no serious adverse events. Covaxin also showed enhanced humoral and cell-mediated immune responses in Phase 2.

The company said that a total of 380 healthy children and adults were administered two vaccine formulations in as many doses (four weeks apart) in a double-blind phase 2 trials. In a double-blind clinical trial, a gold standard for testing new medicines or vaccines, neither the company nor the participants know who receives vaccines and who gets placebos, which maybe a similar-looking injection having no medical effect. Only an independent review board has access to that information.

In a follow-up of the Phase 1 trials, Covaxin produced high levels of neutralising antibodies that remained elevated in all participants three months, at the 104th day, after the second vaccination. “Based on these results, we hypothesise that BBV152 can generate antibodies that may persist for 6-12 months,” Bharat Biotech said in its research paper.

Covaxin is being developed by Bharat Biotech in collaboration with the Indian Council of Medical Research and the National Institute of Virology. It has recruited 13,000 of the 26,000 volunteers for the ongoing Phase 3 trials, which began in mid-November.

India has recorded 1,01,23,778 cases of the coronavirus – the second highest in the world – and 1,46,756 people have died of the infection. Along with Bharat Biotech, the Pune-based Serum Institute, and pharmaceutical company Pfizer have applied for emergency use authorisation in India.

The government has not signed a deal for a coronavirus vaccine yet so it is unclear when it will be available for use in the country. It is likely that the Centre may approve some coronavirus vaccines over the next few weeks. The final call on the efficacy of a vaccine will be taken by the Drugs Controller General of India.