‘Delhi outbreak shows herd immunity against Delta variant difficult’

The study, published in the journal Science, also found that the Delta variant was between 30-70 per cent more transmissible than previous SARS-CoV-2 lineages in Delhi. Herd immunity is a form of indirect protection from a disease that can occur when a sufficient percentage of a population has become immune to an infection. The latest study used genomic and epidemiological data, together with mathematical modelling, to study the outbreak.

The work was led by the National Centre of Disease Control and the Council of Scientific and Industrial Research-Institute of Genomics and Integrative Biology (CSIR-IGIB) in New Delhi with collaborators from the University of Cambridge and Imperial College London, UK, and the University of Copenhagen, Denmark.

“The concept of herd immunity is critical in ending outbreaks, but the situation in Delhi shows that infection with previous coronavirus variants will be insufficient for reaching herd immunity against Delta,” said study co-author Professor Ravi Gupta from the University of Cambridge.

“The only way of ending or preventing outbreaks of Delta is either by infection with this variant or by using vaccine boosters that raise antibody levels high enough to overcome Delta’s ability to evade neutralisation,” Gupta added.