Covaxin booster dose may give long-term immunity: Bharat Biotech

Booster shot of Bharat Biotech’s whole-virus inactivated Covid-19 vaccine Covaxin (BBV152) may give long-term immunity against Sars-CoV-2 infection, showed a study.

The Hyderabad-based vaccine maker said on Saturday that the booster dose study showed ‘promising’ results. The phase 2, double blind, randomised controlled Covaxin trial demonstrated long-term safety with no serious adverse events, it said. The booster shot was given six months after the second Covaxin dose.

“The analysis showed, six months after a two-dose BBV152 vaccination series cell-mediated immunity and neutralising antibodies to both homologous (D614G) and heterologous strains (Alpha, Beta, Delta, and Delta plus) persisted above baseline, although the magnitude of the responses had declined,” the company said.

Furthermore, neutralising antibodies against homologous and heterologous SARS-CoV-2 variants increased 19- to 265-fold after a third vaccination, it added. “Booster BBV152 vaccination is safe and may be necessary to ensure persistent immunity to prevent breakthrough infections,” Bharat Biotech said.

Krishna Ella, Chairman and Managing Director of Bharat Biotech said: “These trial results provide a strong foundation towards our goal to provide Covaxin as a booster dose. Our goals of developing global vaccines against COVID-19 have been achieved with Covaxin indicated for adults, children, 2 dose primary and booster doses. This enables the use of Covaxin as a universal vaccine.”

Both T cell (memory cells) and B Cells (which produce antibodies) durable and neutralising responses were detected, which suggests good immune memory responses and long term protection from severe disease, the Hyderabad-based company said.

Also, 90% of recipients had a detectable neutralising antibody response against the wild-type strain six months after the second dose. “Neutralisation titers against wild-type and Delta variants were 5 times higher than after a two-dose schedule. Similar increases in neutralising antibodies against Alpha, Beta, Delta plus were observed,” the company said.

It added: “The booster dose led to a pronounced increase in CD4+ T- and CD8+ T cell response. This may allow Covaxin to confer long term protective efficacy against severe SARS-CoV-2.”

T cells are grouped into two sub-types – CD4+ and CD8+. Now CD4+ cells are the helper T cells, which help the activity of other immune cells by releasing cytokines, which in turn, prime the B cells. B cells then produce antibodies to neutralise the pathogen. CD8+ T cells, on the other hand, directly kill the infected cells.

Bharat Biotech claimed that the frequency of adverse events was lower than vaccines from other manufacturing platforms.

While protection against the severe disease remains high across the full 6 months, a decline in efficacy against symptomatic disease over time and the continued emergence of variants are expected. Based on emerging data, Bharat Biotech believes that a third dose may be beneficial to maintain the highest levels of protection.

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