A study on the Covid-19 pandemic has revealed that the Delta variant infected previously exposed people in Delhi during the second coronavirus wave this year. The study, published in the journal Science, highlighted the challenges of reaching herd immunity against the Covid delta variant.
Further, the study also found that the Delta variant was between 30-70% more transmissible than previous SARS-CoV-2 lineages in the national capital.
Since the beginning of the Covid-19, Delhi has experienced multiple outbreaks in June and September, and November 2020.
The Covid situation became worse in April this year when daily cases increased from approximately 2,000 to 20,000 between March 31 and April 16.
This was accompanied by a rapid rise in hospitalisations and ICU admissions, severely stressing the healthcare system, with daily deaths spiking to levels three-fold higher than previous waves.
“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,” study co-author Professor Ravi Gupta from the University of Cambridge said.
According to Gupta, vaccine boosters can prevent the Covid crisis in Delhi. “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.
Further, the study talked about the presence of other Covid variants in Delhi during March and May. The researchers said that the Alpha variant increased in Delhi to about 40% of cases in March this year before it was displaced by a rapid increase in the Delta variant in April.
Applying mathematical modelling to the epidemiological and genomic data, the researchers found that the Delta variant was able to infect people who had previously been infected by SARS-CoV-2.
To look for actual evidence of reinfection to support their modelling work, the researchers examined a group of people recruited by CSIR.
In February, 42.1 per cent of unvaccinated subjects participating in the study had tested positive for antibodies against SARS-CoV-2.
In June, the corresponding number was 88.5 per cent, suggesting very high infection rates during the second wave of the outbreak in the country.
Among 91 subjects with prior infection before Delta, about one-quarter (27.5 per cent) showed increased levels of antibodies, providing evidence of reinfection.
When the team sequenced all the samples of vaccination-breakthrough cases at a single centre throughout the study, they found that among 24 reported cases, Delta was seven-fold more likely to lead to vaccination breakthrough infections than non-Delta lineages.
(With PTI inputs)
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