New Delhi: Breakthrough Covid infections were predominantly caused by the Delta variant of the SARS-CoV-2 virus during the second wave in India, a study published earlier this month has found.
Breakthrough Covid infections are infections among people who have contracted Covid despite being fully vaccinated.
The study conducted by a team of the Indian Council of Medical Research (ICMR) among Covid patients in Chennai found that the percentage of people who got infected with the Delta variant was the same among those who were vaccinated and those who were not. However, the prevalence of severe illness or death from Covid was significantly less among the vaccinated individuals.
The findings of the researchers from ICMR’s National Institute of Virology in Pune and National Institute of Epidemiology were published in the Journal of Infection on 5 August. The data was collected from patients screened at centres established by the Greater Chennai Corporation in May.
Three triaging centres — one each from the northern, central and southern parts of Chennai — were selected for the study, which was conducted at the time when India was experiencing the devastating second Covid wave.
Of the 3,790 Covid patients who visited the triage centres between 3 May and 7 May, 373 reported receiving at least one dose of vaccine 14 days prior to their Covid diagnosis and the remaining 3,417 were unvaccinated.
The study enrolled 354 of the 373 vaccinated patients. Of these, 241 had taken one dose of the vaccine, and 113 had taken two doses. The study also included 185 of the 3,417 unvaccinated Covid patients.
Most of the study participants were male, and the proportion of patients with comorbidities was not different in the three groups.
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Delta variant dominant circulating strain
The researchers were able to retrieve genomic sequences from 414 of the 539 samples. The team found that B.1.617.2 (Delta variant) was the predominant variant of concern. As much as 72.4 per cent of the unvaccinated, 68.1 per cent of the partially vaccinated and 74.3 per cent of the fully vaccinated patients were infected with the variant.
The researchers were also able to isolate AY.1 (Delta Plus variant) from five study participants. Of the five patients with AY.1 infection, one required hospitalisation for oxygen support and the rest had a mild form of the disease, the researchers said.
The findings indicate that the prevalence of B.1.617.2 was not different between the vaccinated and unvaccinated groups.
This is not surprising, however, since the Delta variant was the dominant circulating strain and one of the primary drivers for the second wave of Covid in India, according to the researchers.
Moreover, previous studies estimate that the Delta variant can reduce the antibody levels in vaccinated individuals.
“This might be the reason for the breakthrough infections observed in the fully vaccinated individuals. However, the proportion of patients progressing to severe illness and mortality was lower in the vaccinated group,” the researchers said.
The team recommends that along with vaccines, non-pharmaceutical interventions such as masking, social-distancing and ventilations must continue to slow down the transmission.
(Edited by Paramita Ghosh)
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