A community-based cohort study in Chennai estimated 61 per cent vaccine effectiveness of two doses of Covishield vaccine against delta variant infection among people above 45 years⁩. The study was conducted by ICMR-National Institute of Epidemiology and Greater Chennai Corporation from May to September 2021 in a selected geographic area in the city.

The vaccine’s effectiveness against Covid-19 disease in the 45 and above age group was 61.3 per cent at least two weeks after receiving the second dose of Covishield. Two-dose coverage of Covishield in the 18+ and 45+ age group was 18 per cent and 31 per cent, respectively. Genomic analysis of 74 out of the 90 ‘aliquots‘ collected from the 303 COVID-19-positive individuals in the 45+ age group showed delta variants and their sub-lineages.

“We demonstrated the effectiveness of two doses of the Covishield vaccine against the delta variant in the general population of Chennai. We recommend similar future studies considering emerging variants and newer vaccines,” the report said.

“We may require similar VE studies at the population level in the context of changing variants and newer vaccines and boosters,” it added.

“The disease surveillance (including hospitalisation) and vaccination program databases are currently unlinked, limiting the opportunities for systematic periodic analysis of vaccine effectiveness. Effective linkages between databases help countries such as the UK report real-time vaccine effectiveness analyses,” the report said.

“We recommend linkages between the disease surveillance and vaccination databases at the national and state levels to enable regular, in-depth, real-time analysis of vaccine effectiveness. Our study supports that a high vaccination coverage with two doses should be ensured to maintain immunity against Covid-19 infection,” the report said.

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