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Covid-19 vaccines could be 8 times less effective against Delta variant: Study

The study was conducted on 100 healthcare workers at three centres in India, including Delhi’s Sir Ganga Ram Hospital.
By hindustantimes.com | Written by Karan Manral | Edited by Meenakshi Ray, New Delhi
UPDATED ON JUL 06, 2021 06:39 AM IST

Delta variant of the coronavirus is eight times less sensitive to antibodies generated by vaccines against Covid-19 as compared to the original strain of the SARS-CoV-2 virus, which was first detected in China's Wuhan, a study has found. This could mean the Covid-19 vaccines are eight times less effective on the Delta variant, or the B.1.617.2 strain which was first found in India, as compared to their effect on the original virus strain.

According to news agency PTI, the study was conducted on more than 100 healthcare workers at three centres in India, including Delhi’s Sir Ganga Ram Hospital. The joint research, SARS-CoV-2 B.1.617.2 Delta Variant Emergence and Vaccine Breakthrough: Collective Study, was conducted by scientists from India and their counterparts from the Cambridge Institute of Therapeutic Immunology and Infectious Disease. "Across all scenarios considered, our results suggest the Delta variant is both more transmissible and better able to evade prior immunity elicited by the previous infection as compared to previously circulating lineages," it said, according to PTI.

The study said that a combination of evasion of neutralising antibodies in previously infected people, and increased virus infectivity resulting in the second wave is behind the dominance of the Delta variant in India, PTI reported. It also found that severe Covid-19 infection in fully vaccinated HCWs is "rare." However, the study termed as "concerning" cases of breakthrough transmission clusters in hospitals associated with the Delta variant. This, it said, means infection control measures need to stay even in a post-vaccination era.

Analysing the recent data and the dominance of fresh infections due to this variant, the study concluded that the B.1.617.2 strain "appears to be more transmissible" than the B.1.617.1 found in the United Kingdom.

The paper, however, also assured large-scale vaccination will likely protect against moderate to severe disease, and also reduce hospitalisations due to the Delta variant. Giving an example, it said the progression to severe disease and death was found to be "low" even in studies concerning the B.1351 strain, which, it said, is the variant with the least sensitivity to neutralising antibodies. Also known as the Beta variant, it has demonstrated lower protection for at least three Covid-19 vaccines, the paper said.


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