Bharat Biotech, the developer and manufacturer of the inactivated whole-virion Covid-19 vaccine –COVAXIN– after completing its phase 2 trial, claimed that a booster dose of the vaccine 6 months after the second dose demonstrated long-term safety with no serious adverse events. 

The company, announcing the results of the booster dose trial, said that the vaccine showed durable neutralising, T and B cell responses, and 90 percent of recipients had a detectable neutralising antibody response against the wild – type strain when taken 6 months after the second dose.

According to the findings, the vaccine’s 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 also observed. The booster dose led to a pronounced increase in CD4+ T- and CD8+ Tcell response. This may allow COVAXIN  to confer long term protective efficacy against severe SARS-CoV-2, the company said, adding that the frequency of adverse events was lower than vaccines from other manufacturing platforms.

COVAXIN was the first vaccine in India to report safety and immunogenicity results from a booster clinical trial. The analysis, according to the company, showed that the third dose after six months of the two-dose BBV152 vaccination series, the cell-mediated immunity and neutralising antibodies to both homologous (D614G) and heterologous strains (Alpha, Beta, Delta, and Delta plus) persisted above baseline. However, the magnitude of the responses had declined, it said. 

The results also showed that the neutralising antibodies against homologous and heterologous SARS-CoV-2 variants increased 19 to 265 fold after a third vaccination.