Covaxin effective against new Delta Plus variant, says study

Covaxin can effectively neutralise the Delta Plus (AY.1), the vaccine’s manufacturer Bharat Biotech said citing laboratory studies it carried out along with the Indian Council of Medical Research. The study, which is yet to be peer-reviewed, showed that the vaccine’s ability to neutralise the variants was lower than what was seen with the ancestral version of the Sars-Cov-2, similar to what has been seen with the case of other vaccines.

The scientists carried out lab tests with antibodies derived from three groups of people – those who had two doses of vaccines but no infection, those had both doses of the vaccine after recovering from Covid-19 and those who had Covid after getting both doses (breakthrough infections).

These antibodies were then made to react with three variants – Delta, Delta Plus and B.1.617.3, as well as the B.1 (the version prior to the mutation).

The study found neutralising antibodies, which bind to the Sars-CoV-2 virus, was the higher in people who had the infection along with vaccination, rather than those who just received the vaccines. But, the authors said, there wasn’t significant reduction in antibody levels against the variants as compared to the original one in those who received only the vaccine. The blood serum of recovered cases with vaccinations and breakthrough cases had considerable fold-reductions, said the study.

“Vaccine is showing very high neutralizing titre in all three categories of sera whether it’s full vaccinated, recovered cases with vaccination or breakthrough cases. The titres of recovered cases with vaccination or breakthrough cases are very high... Natural infection offers good protection,” said Dr Pragya Yadav, senior scientist at Natio-nal Institute of Virology and one of the authors of the paper.

“But after some time the antibody titres drop; immunization boosts it. That is why people should get immunized after recovery.”

To be sure, neutralising antibody titers do not reflect efficacy rates, which are based on a vaccine’s real-world ability to prevent symptomatic infection. Bharat Biotech in June said the final efficacy estimates, based on its phase 3 trials, showed Covaxin had an efficacy rate of 77.8% against the Sars-Cov-2 virus that most closely resembles the origin virus, and 65.8% against the Delta variant, which is now predominant in India.

The reduction in neutralising activity in the latest study was observed in fully vaccinated individuals who never had Covid-19 was seen to be 1.3, 1.5, 1.9-fold against Delta, AY.1, and B.1.617.3. Similarly, the reduction in neutralising titre in those who had an infection and were then immunised was 2.5, 3.5, 3.8-fold, and in those who had a breakthrough infection it was 1.9, 2.8, 3.5-fold when compared against the corresponding neutralisation levels seen in people with the ancestral version of variants.

“What this essentially means is get vaccinated. It is great news that all the vaccines seem to be working against all the variants...,” said Dr T Jacob John, former head of the department of virology at Christian Medical College-Vellore