Vaccine effectiveness of Covishield against SARS-CoV-2 infection in fully vaccinated individuals was found to be 63% even as it offered 81% protection from moderate-to-severe disease, according to a new study published in The Lancet Infectious Diseases journal.
Studies from England and Scotland have reported effectiveness of 60 to 67% for the vaccine against infection by the Delta variant. Breakthrough infections due to the Delta variant have been reported after vaccination with mRNA vaccines, researchers said.
The scientists also observed that the spike-specific T-cell responses were conserved against both the and wild-type SARS-CoV-2.
Such cellular immune protection might compensate for waning humoral immunity against the virus variants and prevent moderate-to-severe disease and need for hospitalisation,” according to a statement by the Science and Technology ministry.
This study includes a comparison between 2,379 cases of confirmed SARS-CoV2 infection and 1,981 controls. Researchers conducted the study at two medical research centres in Faridabad. Of the confirmed infection cases, 85 (3.6%) were from the fully vaccinated group compared with 168 (8.5%) from the control group
This study provides comprehensive data on the real-world vaccine effectiveness and immunological response to vaccination which should help guide policy, the statement from the ministry added.
A multi-institutional team of Indian researchers led by Translational Health Science and Technology Institute (THSTI) evaluated the real-world vaccine effectiveness of Covishield during the SARS-CoV-2 infection surge between April and May, 2021 in India.
They also assessed neutralising activity and cellular immune responses against the variants in healthy, vaccinated persons to understand the mechanisms of protection.
Studies from England and Scotland have reported effectiveness of 60 to 67% for the vaccine against infection by the Delta variant. Breakthrough infections due to the Delta variant have been reported after vaccination with mRNA vaccines, researchers said.
The strengths of this study funded by the Department of Biotechnology, Council of Scientific and Industrial Research, India, and Fondation Botnar are use of the WHO-recommended test-negative, case-control design, which balances risk profile, health-care seeking behaviour, and access to care among vaccinated and non-vaccinated people, and the comparability of the vaccine effectiveness estimates with those of randomised trials.
The ChAdOx1 nCoV-19 vaccine remained effective against moderate-to-severe Covid-19 even during a surge that was dominated by the highly transmissible Delta variant of SARS-CoV-2. Spike-specific T-cell responses were maintained against the Delta variant, the study said.
Although neutralising antibodies might prevent symptomatic disease, cellular immune responses might prevent severe infection. Our study has shown that complete vaccination protected against moderate-to-severe Covid-19 even when the Delta variant was dominant, researchers said.
It has been argued that breakthrough infections should only be diagnosed if a vaccinated person develops lower respiratory tract involvement since the vaccines are not designed to provide nasopharyngeal mucosal immunity. Our findings support this viewpoint that cellular immune responses might salvage reduced neutralising ability and prevent severe disease among vaccinated people even though protection against infection is compromised, the researchers added.
In its latest risk assessment for SARS-C0V-2 variants, Public Health England (PHE) has said a staggering 61% of the samples sequenced are now of the Delta variant (B.1.617.2). This means the Delta variant, first detected in India, is more dominant in the UK than the Alpha variant that had last year triggered a surge in the UK.
https://indianexpress.com/article/explained/covid-delta-variant-coronavirus-cases-7344758/
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