While the Delta variant mutated into ‘Delta Plus’, first detected in India in April 2021, researchers decided to study the efficacy of the Covaxin vaccine. They have found that despite a slight reduction in neutralisation antibody titres, the vaccine remains effective against the Delta, AY.1 (Delta Plus) and B.1.617.3 variants. Covaxin has been developed by Bharat Biotech and the Indian Council of Medical Research (ICMR).
The Delta variant of SARS-CoV-2 has been classified as a variant of concern (VoC) by the World Health Organization. Apart from being associated with the second wave in India during March-May this year — it is estimated to be responsible for 90% of the cases reported in the country — the variant has spread across nearly 99 countries and been found to be more infectious than the Alpha, Beta and Gamma variants. The Delta variant has also been identified as the leading cause of breakthrough infections globally among vaccinated individuals.
Recently, the Delta variant has mutated into the sub-lineages Delta AY.1, AY.2 and AY.3. Of these, the apparently highly infectious Delta AY.1 (Delta Plus) variant was first detected in India in April 2021, and subsequently in 20 other countries as well.
The prevalence of Delta AY.1, however, has been relatively low so far. Genome sequencing by INSACOG (Indian SARS-CoV-2 Genomics Consortium) has found 70 cases of Delta Plus.
So far, no information was available on the efficacy of currently available vaccines against the Delta Plus variant. It is also uncertain whether Delta Plus is associated with higher transmissibility, severe disease, and evasion of immune response compared to the Delta variant.
The possibility of the variant escaping the immune response has been a major concern during the ongoing vaccination programme. This variant contains an additional mutation (K417N ) in the spike protein and emerging evidence suggests that this mutation could lead to resistance against monoclonal antibodies called casirivimab and imdevimab.
Researchers at ICMR-National Institute of Virology (NIV), therefore, took up the research. They studied the neutralisation activity of the sera of 42 individuals vaccinated with two doses of Covaxin, 14 recovered cases after two vaccine doses, and 30 breakthrough cases after two doses against the Delta, Delta AY.1, and B.1.617.3 variants, compared to the B.1 variant.
“Our research study showed that Covaxin vaccine could still neutralise Delta, AY.1 and B.1.617.3 variants,” Dr Samiran Panda, Head of Epidemiology and Communicable Diseases, ICMR told The Indian Express. Sera of vaccines — Covid-naïve, recovered cases with full vaccination, and breakthrough cases —demonstrated 1.3, 2.5 and 1.9-fold reduction against the Delta variant in comparison to the B.1 variant respectively, said the study, ‘Comparable neutralisation of SARS-CoV-2 Delta AY.1 and Delta in individuals sera vaccinated with BBV152, published on the preprint server bioRxiv.
Lead author Dr Pragya Yadav said a minor reduction was observed in the neutralising antibody titre in recovered cases , fully vaccinated and post-immunised infected cases as compared to Covid-naive vaccinated individuals. “However, with the observed high titres, the sera of individuals belonging to all the groups in the study would still neutralise the Delta, Delta AY.1 and B.1.617.3 variants effectively,” Dr Yadav said.
In a previous study, Covaxin had demonstrated 77.8% effectiveness against symptomatic Covid-19 and 65.2% protection against the Delta variant, according to Bharat Biotech.
In this new study, despite the sera of vaccinated Covid-recovered cases and those of breakthrough cases showing considerable reduction in the neutralisation antibody titre, Covaxin could still neutralise Delta, AY.1 and B.1.617.3 variants. “The bottom line is that Covaxin is effective and a slight reduction in neutralisation antibody titres is not going to be detrimental for the vaccination programme,” Dr Panda said.