A single dose of the Covid-19 vaccine could be sufficient for adults who have already been infected with the virus, two recent studies in India suggest. The WHO and the Union ministry of health and family welfare have recommended getting both shots of double-dose vaccines, but authors of the studies said their findings could help promote “judicious” use of vaccines and larger population coverage.
The first study was conducted by researchers at the AIG Hospital, a tertiary care facility in Hyderabad, results of which were published in ‘The International Journal of Infectious Diseases’ in May. They enrolled 280 healthcare workers vaccinated between January 16 and February 5. They were divided into two groups — those who had been infected with Covid-19 (131) and those who hadn’t (149). All of them were vaccinated with two doses of Covishield, 28 days apart, going by government guidelines in place then. Blood samples were taken at the beginning and at the end of the study, and tested for two things — antibodies and memory cells (immune cells which can recognise a foreign particle encountered previously).
“At the end of four weeks, we found the Covid-19 group had developed 1,000 units of antibodies, 10 times that generated in the non-Covid-19 group,” said Dr D Nageshwar Reddy, a co-author of the study and chairperson of AIG Hospital. As for the memory cells — called T-cells and B-cells, which form a major part of our immune response — they found better response in the Covid-19 group. “There are two types of T-cells, Cd4 and Cd8. Response of both was three times higher in the Covid-19 group than the other,” he added. On that basis, he further said, “Our suggestion is to just take just one dose.”
The other study was conducted by the Banaras Hindu University in April, which has been accepted for publication in ‘Science Immunology’. Prof Gyaneshwar Chaubey from the department of zoology headed the study, conducted on a smaller scale of 20 people, half of whom had been infected and half hadn’t. Both groups were administered one dose of Covishield and their antibodies were checked every week, for a month.
“The group which had Covid-19 earlier developed antibodies in the first and second week, in a high and robust amount. In the other group, 90% of the participants developed antibodies but only in the third and fourth weeks. The remaining 10% didn’t develop any antibodies even after 10 weeks,” said Chaubey. In this study, researchers found, those who had been exposed to the virus earlier developed double the antibodies (400 titers) than those who hadn’t (200 titers). “Considering the vaccine shortage, the study could lead to wider vaccine coverage in a shorter time,” Chaubey said.