NEW DELHI: The delta variant driving the second COVID-19 wave in India has been found to be up to 40 per cent more transmissible than previously circulating lineages and is able to evade up to 55 per cent of the immune protection provided by prior infection with non-delta variants, besides reducing neutralization by vaccines, said a new study.
The study by a group of scientific institutes from India, UK and hospitals in the country found that the delta variant shows a reduced sensitivity of approximately eight times to vaccine-elicited antibodies compared to the wild type Wuhan-1 bearing D614G. The team includes members from the Indian SARS-CoV-2 Genomics Consortium (INSACOG).
The delta variant has significant immune evasion and fitness compared to the alpha variant. Vaccines will prevent severe disease/death in most people, but special measures may be needed for those who respond poorly to vaccination. Infection in vaccinated HCWs needs to be considered.
“Severe disease in fully vaccinated HCW was rare, breakthrough transmission clusters in hospitals associated with the delta variant are concerning and indicate that infection control measures need to continue in the post-vaccination era,” it said.
The SARS-CoV-2 B.1.617.2 (delta) variant was first identified in Maharashtra in late 2020 and has spread throughout India, displacing the B.1.1.7 (alpha) variant and other pre-existing lineages. The delta variant is less sensitive to neutralising antibodies in sera from recovered individuals, with higher replication efficiency as compared to the alpha variant.
In an analysis of vaccine breakthroughs in over 100 healthcare workers across three centres in India, the delta variant not only dominates vaccine-breakthrough infections with higher respiratory viral loads compared to non-delta infections, but also generates greater transmission between HCW as compared to B.1.1.7 or B.1.617.1.
“Serum neutralising titres against the SARS-CoV-2 Delta variant were significantly lower in participants vaccinated with ChadOx-1 (Covishield) as compared to BNT162b2 (Pfizer-BioNTech). These combined epidemiological and in vitro data indicate that the dominance of the Delta variant in India has been most likely driven by a combination of evasion of neutralising antibodies in previously infected individuals and increased virus infectivity,” it added.