If previously Covid-19 infected, single Covaxin dose draws same antibody response as two doses

India's first indigenous Covid-19 vaccine Covaxin, codenamed BBV152, was approved by the government for emergency use in January

A single shot of Covaxin – the homegrown Covid-19 vaccine - in Covid exposed individuals is as good as two doses in people who didn't have the infection, the Indian Council of Medical Research said on Saturday, on the basis of a preliminary study.

The ICMR team set out to examine an idea proposed by international experts to deal with vaccine shortage - those who had the infection should be given a single shot in order to free up more doses so that others who didn’t develop the infection, can take both the doses. There were supporting studies with other Covid-19 vaccines to back up such a claim.

To test the idea for the indigenous vaccine, the researchers collected blood from 114 health workers and front line staff, of whom 30 had either prior Covid-19 infection or exposure. Their blood samples were analysed before the Covaxin shot and after the first and second doses to measure the levels of neutralising antibody and other protective molecules.

"Overall, good vaccine-induced antibody responses were seen in prior SARS-CoV-2–infected individuals, except in two cases,” the team reported in the Indian Journal of Medical Research.

“Our results in a varied group of healthcare professionals and frontline workers lend support to the previous studies (albeit mainly focused on mRNA vaccines) that increased levels of SARS-CoV-2 binding and neutralizing antibodies are present after a single vaccine dose in previously infected individuals and are comparable to the levels seen after two doses in those without prior infections.”

However, both vaccine doses would be ideal even for previously infected individuals in the long run due to the occurrence of variants of concern.

The findings were released at a time when the Union Health Ministry is in the process of finding out ways to vaccinate the target population of 94.47 crore. So far 50% of that population received a single shot while less than one-fifth is fully vaccinated.

The researchers admitted that the study has several limitations including its small sample size because of which many questions could not be answered. They proposed a larger size cohort study to find out answers to such queries.