The higher ability of the Delta variant of the SARS-CoV2 virus to infect and evade the immune response built through previous infections or vaccines can be the possible explanation behind the rapid spread of this particular variant, which has created havoc in the western world in the second phase of the Covid-19.
In a study published in Nature journal, a team of researchers from India and other countries has found that the Delta variant (or B.1.617.2 lineage) was eight times more likely to escape immunity gained through AstraZeneca or Pfizer vaccines compared to the original virus. Also, the Delta variant was six times more likely to re-infect people who have recovered from Covid-19.
The study also found “higher replication efficiency†in the Delta variant, giving it a better capability to infect and “potentially explaining the B.1.617.2 dominanceâ€.
The study said “increased replication fitness†and “reduced sensitivity†to neutralising bodies, built either through natural infection or vaccines, had contributed to the rapid spread of the Delta variant in more than 90 countries.
The researchers also studied breakthrough infections amongst almost 9,000 fully vaccinated healthcare workers in three Delhi hospitals.
A total of 218 workers at these hospitals had symptomatic infections even after taking both doses of the Covishield vaccine.
The prevalence of the Delta variant in this cohort was found to be 5.45 times more than other variants.
B.1.617.2 Delta variant, was first observed in India in late 2020. It has since spread around the globe - in the UK, it is responsible for nearly all new cases of coronavirus infection.
Professor Ravi Gupta from the Cambridge Institute of Therapeutic Immunology and Infectious Disease at the University of Cambridge, one of the study’s senior authors, said, “By combining lab-based experiments and epidemiology of vaccine breakthrough infections, we’ve shown that the Delta variant is better at replicating and spreading than other commonly-observed variants.
“There’s also evidence that neutralising antibodies produced as a result of previous infection or vaccination are less effective at stopping this variant.
“These factors are likely to have contributed to the devastating epidemic wave in India during the first quarter of 2021, where as many as half of the cases were individuals who had previously been infected with an earlier variant.â€
Dr Partha Rakshit from the National Centre for Disease Control, Delhi, joint senior author, added, “The Delta variant has spread widely to become the dominant variant worldwide because it is faster to spread and better at infecting individuals than most other variants we’ve seen. It is also better at getting around existing immunity - either through previous exposure to the virus or to vaccination - though the risk of moderate to severe disease is reduced in such cases.â€
Professor Anurag Agrawal from the CSIR Institute of Genomics and Integrative Biology, Delhi, also, joint senior author, added, “Infection of vaccinated healthcare workers with the Delta variant is a significant problem. Although they themselves may only experience mild Covid, they risk infecting individuals who have suboptimal immune responses to vaccination due to underlying health conditions - and these patients could then be at risk of severe disease.
“We urgently need to consider ways of boosting vaccine responses against variants among healthcare workers. It also suggests infection control measures will need to continue in the post-vaccine era.â€
