Despite Delta’s ability to reduce the humoral / antibody-induced immune response, cell-mediated immunity – the immunity induced by T cells at sites of infection – was still well preserved and may increase the efficacy of the drug. vaccine, according to study by leading Indian researchers. institutions have shown.
The study indicates that although infection can occur in a vaccinated individual, protection against severe Covid-19 disease can be attributed to cell-mediated immunity.
Covishield, the brand name of the vaccine developed by Oxford-AstraZeneca and manufactured by the Serum Institute of India, is key to India’s Covid-19 vaccination program.
The study paper is a preprint currently being submitted to the renowned global journal, The Lancet.
The government-funded study was led by the Translational Health Science and Technology Institute in Faridabad and in partnership with the CSIR – Institute of Genomics and Integrative Biology, the National Institute of Immunology and the India Consortium for Covid-19 research.
The study indicates that two doses of the vaccine should be encouraged and calls for further epidemiological public health measures to overcome the threat posed by Delta and other emerging variants of SARS-CoV-2.
“Our study showed that full and even partial vaccination protected against severe Covid-19 even in the case of the worrying B.1.617.2 variant, an observation shown earlier consistently against the wild-type virus,” says- he does.
All preliminary studies on the Delta variant so far have shown that it has a greater ability to evade the vaccine-induced immune response.
British studies so far have shown the vaccine to be 59.8% effective against variant B.1.617.2, which has shown the highest rate of transmission to date.
New Indian study reinforces that the Covishield vaccine is “modestly protective against infection attributed to the SARS-CoV-2 Delta variant during the recent massive wave but provided higher protection against moderate to severe illnesses requiring hospitalization “.
He adds, however, that there was a significant reduction in the protective humoral immune response against the Delta variant in Covishield vaccine recipients, but cell-mediated immunity was well maintained.
“While neutralizing antibodies can prevent symptomatic disease, cellular immune responses can prevent serious disease…. This view is consistent with our findings that cellular immune responses could save reduced neutralizing capacity and prevent serious illness in vaccinated people, even if protection against infection is compromised, ”he said.
The study was carried out on 2,766 people affected by Covid 19 – mainly by the Delta variant – between April 1 and May 31.
The results showed that full vaccination prevented moderate-severe Covid-19 in 81.5% of cases. The efficacy of the single-dose vaccine was 46.2% against infection but 79.2% in preventing moderate-severe Covid-19.
There were 16 deaths in the unvaccinated or incomplete vaccination group but none in those fully vaccinated.
In the case of Delta, the study found a significant reduction in neutralization and the mutated proteins were shown to escape even monoclonal antibodies used in the clinic.
“However, while neutralizing antibodies are important in preventing entry of the virus into host cells, an important defense mechanism is the cellular immune response against the virus,” he adds.
The study found that T cell responses were preserved against antigens in the recombinant mutant receptor binding domain, suggesting cell-mediated immune protection.
“Although CD4 + and CD8 + T cell responses are essential for viral clearance, it has been reported that CD4 +, compared to CD8 +, the T cell immune response in SARS-CoV-2 is more important for controlling infection with SARS-CoV-2, ”he explains.
The study is entitled “Cellular immune responses are preserved and may contribute to the efficacy of the ChAdOx1 nCoV-19 vaccine against infection due to the delta variant of SARS-CoV-2 B · 1 · 617 · 2 despite a reduced viral neutralization “.