Antibodies produced in response to Covaxin were reduced when tested against the Delta variant and its sublineages but continued to be high enough to remain protective, according to a study by scientists at the ICMR-National Institute of Virology.
The antibodies were collected from fully vaccinated individuals, some of whom had reported breakthrough infections, and yet others who had recovered from COVID-19 and tested in the laboratory against lab-cultured coronavirus variants belonging to the Delta, AY.1 and AY.3 lineages.
In the vaccinated group, consisting of 42 individuals but who had not been infected with COVID-19, the neutralising antibodies were reduced by about 23% when tested against the Delta variant; 33% against AY.1 and nearly 47% against AY.3. These reductions were in comparison to a reference variant called B.1.
In those vaccinated, who'd had COVID, the average number of antibodies produced was much higher, nearly 2.5 times higher than in those who'd never had COVID-19. However the reductions were sharper — a nearly 60% reduction when faced with the Delta variant, 70% compared to AY.1 and about 72% with AY.3.
The highest average neutralising antibodies were those in individuals with breakthrough infections, or who tested positive despite two doses. Their average antibody levels were nearly thrice that of the COVID-naive individuals but reduced by nearly 50% when tested against the Delta variant, by 65% against AY.1 and 72% against AY.3.
“This demonstrates the possible role of memory cells in immune boosting with post-infection or infection after immunization. The comparative analysis of all the groups revealed that the B.1.617.3 (AY.3) variant seems to be less susceptible to neutralisation followed by Delta AY.1 and Delta variants compared to B.1,” the authors who include several senior scientists from the ICMR, note in their preprint publication, which is yet to be peer-reviewed.
Despite these reductions, the authors aver, the antibody levels remained protective. “However, with the observed high titers, the sera of individuals belonging to all the aforementioned groups they would still neutralize the Delta, Delta AY.1 and B.1.617.3 (AY.3) variants effectively,” they note.
India is currently registering about 40,000 new cases everyday with sharp increases in Kerala and several northeastern States. Most of the cases are believed to be caused by the parent Delta variant.
An ICMR study says that in cases involving the Delta variant, only 9.8% cases required hospitalisation while fatality was around 0.4%. However the prevalence of variants AY.1 and AY.3 are extremely low according to the India Sars CoV2 Genome variation consortium (INSACOG) which tracks coronavirus variants and based on their analysis of about 50,000 genomes or about 0.1% of India's confirmed coronavirus cases.