'Delta variant breaks through vaccine more than others'

Delta variant dominates vaccine-breakthrough infections among hospital staff: Study

It also leads to higher respiratory viral loads compared to non-delta infections

Breakthrough infections are those in which a person gets the Covid-19 infection 14 days after receiving the second dose of the vaccine. Credit: iStockPhoto

The highly infectious Delta variant, which is driving the Covid-19 epidemic in India also dominates vaccine-breakthrough infections with higher respiratory viral loads compared to non-delta infections, a new study based on 100 Indian healthcare workers has found.

Using samples from the staff of three Delhi hospitals, an Indo-UK team of researchers has raised red-flags on breakthrough infections caused by the Delta variant in hospitals where patients with comorbidities can pick up the SARS-CoV-2 infections from the staff.

“While severe disease in fully vaccinated healthcare workers was rare, breakthrough transmission clusters in hospitals associated with the Delta variant are concerning and indicate that infection control measures need to continue in the post-vaccination era,” the team reported in a study.

Breakthrough infections are those in which a person gets the Covid-19 infection 14 days after receiving the second dose of the vaccine. Though the number of such infections are not large among the general population, breakthrough infections are being seen among healthcare workers who function in a high-risk environment.

Health officials on Friday pointed out that the variants of concerns – mostly the Delta variants – were present in 174 districts in 35 states and union territories. The proportion of the VoCs has risen from 10.31% in May to more than 51% by June 20th.

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"Everything on Delta, from its increased transmissibility, high viral load and increased immune escape, has been proven now at the molecular level. There is no scope of any speculations,” one of the team members told DH.

The team involves scientists from the University of Cambridge, Medical Research Council, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease, National Centre for Disease Control, CSIR Institute of Genomics and Integrative Biology and Imperial College London besides the doctors from Indraprastha Apollo Hospital.

Vaccine breakthrough clusters amongst healthcare workers, the study says, is of concern given that hospitals frequently treat individuals who may have suboptimal immune responses to vaccination due to comorbidity.

Such individuals are at risk for severe Covid-19 disease if they pick up infections from workers within hospital environments.

The study also reports that Delta variant is 8 times less sensitive to antibodies generated by the AstraZeneca vaccine – manufactured as Covishield in India – and Pfizer vaccines in the laboratory when compared against the original strain that came from Wuhan.

Analysing laboratory measurement-based studies from around the world, the Indian Council of Medical Research has also reported reduced activity of Covishield and Covaxin against the Delta variant. But the residual activity is strong enough for both vaccines to work against the variant.

"Covishield and Covaxin work against the variants of SARS-CoV-2- Alpha, Beta, Gamma and Delta -- that is well established for these two vaccines," asserted Balram Bhargava, director-general of the Indian Council of Medical Research.

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