Two doses of Covishield effectively protected above-45 population from infection: Study

A new study by the National Institute of Epidemiology, Chennai, and National Institute of Virology, Pune, has demonstrated the effectiveness of two doses of Covishield (ChAdOx1) vaccine against the Delta variant of Covid-19 in the general population of Chennai. “Our primary objective was to understand the protective effect of Covid-19 vaccines, irrespective of the severity of the disease in the general population. Two doses of Covishield effectively protected the population above 45 years from Covid-19 infection,” researchers involved in the study have said.

The study “Effectiveness of the ChAdOx1 nCoV-19 Coronavirus Vaccine (CovishieldTM) in Preventing SARS-CoV2 Infection, Chennai, Tamil Nadu, India, 2021” published in Vaccines in its June 17, 2022 edition supports that a high vaccination coverage with two doses should be ensured to maintain immunity against Covid-19 infection. “The study included all sections of a population and hence, generated data closer to the real-world setting,” Dr Prabhdeep Kaur, senior scientist at NIE and principal investigator of the study, told The Indian Express.

“It was challenging to develop a community cohort in a pandemic setting due to the high burden on the health care workers in the field, apprehensions among the population, and poor linkages between disease and vaccination data. Our study reiterates the protective effect of vaccines against RT-PCR-confirmed infection as reported in three other studies from India,” Dr Kaur said.

The community-based cohort study in Chennai was conducted during the declining phase of the second wave (June-September 2021) of Covid-19 in Chennai. The vaccination coverage among the eligible population (18+) began picking up rapidly last year and by May 22, 2021, about 20 per cent of individuals of 45 years of age or above had received both doses of the Covid-19 vaccine. The study’s estimated sample size was 10,232. Researchers enrolled 69,435 individuals, of which 21,793 were above 45 years. Two-dose coverage of Covishield in the 18+ and 45+ agegroup was 18 per cent and 31 per cent, respectively. Genomic analysis of 74 out of 90 aliquots collected from the 303 Covid-19-positive individuals in the 45+ age group showed Delta variants and their sub-lineages. The vaccine’s effectiveness against Covid-19 disease in the ≥45 age group was 61.3 per cent at least two weeks after receiving the second dose of Covishield.

“Our study findings support the hypothesis that two doses of the Covishield (ChAdOx1 nCoV-19) vaccine protected the adult population from Covid-19 infection in Chennai. We may require similar VE (vaccine efficacy) studies at the population level in the context of changing variants and newer vaccines and boosters,” Dr Kaur said.

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 United Kingdom report real-time vaccine effectiveness analyses, the study has said. Researchers have strongly recommended linkages between disease surveillance and vaccination databases at the national and state levels to enable regular, in-depth and real-time analysis of vaccine effectiveness.

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