Covaxin third shot gives long-term immunity: Nature Scientific study

Study shows booster jab is effective against several Sars-CoV-2 strains such as Alpha, Beta, Delta, Delta Plus and Omicron, and also increases memory B-cell response

Bharat Biotech’s Covid-19 vaccine Covaxin’s third dose, delivered six months after the second, increases neutralising antibody responses against several Sars-CoV-2 strains (Alpha, Beta, Delta, Delta Plus and Omicron), as well as memory B-cell response, showed a study published in Nature Scientific Reports.

Bharat Biotech said this study has demonstrated multiple benefits of its vaccine, including long-term immune response, cell-mediated immunity, safety of booster dose, and immunogenicity against the spike protein, N protein and neutralising antibody responses against alpha, beta, delta, delta plus and omicron variants.

“Administration of a third dose six month after the two-dose vaccination dramatically increased  neutralising antibody responses against both homologous and heterologous strains (Alpha, Beta, Delta, Delta Plus and Omicron) and showed increased memory B cell response,” the company said on Wednesday.

Covaxin induced T-Cell or memory cell responses lasted till six months even after antibodies decline.

“These T cell responses have been followed for up to 12 months in vaccinated individuals, irrespective of receipt of third dose. T cell responses in turn help to produce B cell memory response, upon antigen re-exposure. Thus, Covaxin provides long term immunity,” the company noted.

Immune responses declined at 6 months, but increased by 40 fold in subjects who received a booster dose. When assessed against variants of concern immune responses persisted up to 12 months.

“No serious adverse events observed, except pain at the injection site, itching and redness, no cases of myocarditis, pericarditis, blood clots, or thrombocytopenia were detected,” the company claimed.

The study was conducted in around184 subjects, who were randomised 1:1 and received either a booster dose of BBV152 or a placebo, around 6 months after the primary series of 2 doses.