Spread of Delta driven by combination of immune escape, increased infectivity: Nature

Aditi Tandon

Tribune News Service

New Delhi, September 8

The Delta variant of SARS-CoV-2, which has become the dominant variant in countries, including India and the UK, has most likely spread through its ability to evade neutralising antibodies and its increased infectivity, say an international team of researchers including from India.

The findings have just been reported in the leading science journal Nature.

Prof 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: “We have 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, whereas many as half of the cases were individuals who had previously been infected with an earlier variant.”

To examine how well the Delta variant was able to evade the immune response, the team extracted serum from blood samples collected as part of the Covid cohort of the NIHR BioResource. The samples came from individuals who had previously been infected with the coronavirus or who had been vaccinated with either the Oxford/AstraZeneca or Pfizer vaccines. Serum contains antibodies raised in response to infection or vaccination. The team found that the Delta variant virus was 5.7-fold less sensitive to the sera from previously-infected individuals, and as much as eight-fold less sensitive to vaccine sera, compared with the Alpha variant - in other words, it takes eight times as many antibodies from a vaccinated individual to block the virus.

Consistent with this, an analysis of over 100 infected health care workers at three Delhi hospitals, nearly all of whom had been vaccinated against SARS-CoV-2, found the Delta variant to be transmitted between vaccinated staff to a greater extent than the alpha variant.

Professor Anurag Agrawal from the CSIR Institute of Genomics and Integrative Biology, Delhi, joint senior author, added: “Infection of vaccinated health care 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 health care workers. It also suggests infection control measures will need to continue in the post-vaccine era.”