New immunology study highlights importance of COVID vaccination of those who have already been exposed to the virus

Study finds COVISHIELD, COVAXIN vaccines enhance immune responses in those with pre-existing SARS-CoV-2 immunity, mitigating vaccine hesitancy. Researchers from St John’s Research Institute led multi-centric study; funded by Hindustan Unilever. Results suggest persistent anti-COVID-19 immunity up to one year post COVISHIELD vaccination.

A study of COVID-19 vaccine immunity highlights the importance of vaccination in those who have already been exposed to the virus.

The study has found that both COVISHIELD and COVAXIN significantly enhance immune responses in subjects with varying levels of basal immunity to SARS CoV-2 developed through natural exposure. The multi-centric study led by researchers from St John’s Research Institute was published in npj Vaccines, a Nature journal on September 14.

COVISHIELD, manufactured by Serum Institute of India and COVAXIN, indigenously developed by Bharat Biotech Ltd were the first two vaccines authorized for COVID-19 vaccination in India. Even though India had a highly successful vaccination campaign, a majority of the population remained unvaccinated till end of 2021. A major question raised and unknown at that time was whether COVID vaccines available in India in 2021 were even capable of inducing immune responses over and above immunity that may have been acquired through natural exposure to the virus during the ancestral and Delta waves. 

“We addressed this issue in 700 adults (aged 18-44 years) who received their primary series of vaccination between November 2021 and January 2022. The samples were collected till May 2023 following which the analysis was done,” said Annapurna Vyakarnam, whose Human Immunology Laboratory is based at St John’s Research Institute (SJRI). 

The study participants, who were recruited from four clinical sites and five research institutes in Bengaluru, Pune and Vellore, received either two doses of COVAXIN at 28 days apart or two doses of COVISHIELD  at three months apart as per Indian Council of Medical Research (ICMR) guidelines. The peak responses to both these vaccines were measured at two weeks (14 days) post the second dose (day 42 for COVAXIN and day 98 for COVISHIELD).

Professor Vyakarnam, who is the lead immunologist of the study, said circulating neutralising antibodies and cellular T-cell responses are cornerstone immune parameters governing protection from severe disease. “This study probed magnitude, breadth and quality of these immune parameters using advanced immunological techniques and demonstrated all three parameters to be enhanced at two weeks after subjects received their first two doses of either of the COVID-19 vaccines,” said the researcher, who is also affiliated to King’s College London.

In addition, first round data from this group showed evidence of persistent anti-COVID-19 immunity, up to one year post COVISHIELD vaccination, but less so with COVAXIN, she said.