Breakthrough cases and COVID-19 recovered individuals with one or two doses of vaccine have relatively higher protection against Delta variant in comparison to those administered either one or two doses of Covishield, a study stated.

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Prior vaccination results in less severe disease against subsequent infection provide evidence that both humoral and cellular immune response plays an important role in protection, according to the study which is yet to be peer-reviewed and was posted on bioRxiv preprint server on 2 July. The study 'Neutralisation of Delta Variant with Sera of Covishield vaccines and COVID-19 Recovered Vaccinated Individuals' has been done by scientists from the Indian Council of Medical Research (ICMR), National Institute of Virology, Pune, and Department of Neurosurgery, Command Hospital (Southern Command), Armed Forces Medical College, Pune.

The recent emergence of B.1.617 lineage has created grave public health problems in India. The lineage further mutated to generate sub-lineages B.1.617.1 (Kappa), B.1.617.2 (Delta) and B.1.617.3. Apparently, the Delta variant has slowly dominated the other variants. With this, the World Health Organisation has described this sub-lineage as variant of concern, the study stated. "The high transmissibility associated with Delta variant led to the second wave of the pandemic in India which affected millions of people. Besides this, the variant of concern has been reported to show lower neutralisation to several approved vaccines. This has led to breakthrough infections after completion of vaccination regimen," it said.

There is limited information available on the duration of protective immune response post-infection, vaccination or breakthrough infection with SARS-CoV-2. The study evaluated immune response in sera of the Covishield vaccinated individuals belonging to categories-- one dose vaccinated, two doses vaccinated, COVID-19 recovered plus one dose vaccinated, COVID-19 recovered plus two doses vaccinated and breakthrough COVID-19 cases. "The findings of the study demonstrated that the breakthrough cases and COVID-19 recovered individuals with one or two dose of vaccine had relatively higher protection against Delta variant in comparison to the participants who were administered either one or two doses of Covishield. "Prior vaccination results in less severe disease against subsequent infection provide evidence that both humoral and cellular immune response play an important role in protection," the study added.