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Researchers recommend linkages between disease surveillance and vaccination databases to enable in-depth, real time analysis of vaccine effectiveness

Pune: A new study by the National Institute of Epidemiology, Chennai and National Institute of Virology, Pune has demonstrated how two doses of Covishield (ChAdOx1) vaccine have been effective against the Delta variant among 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,” the study researchers have said.

The study, titled “Effectiveness of the ChAdOx1 nCoV-19 Coronavirus Vaccine (CovishieldTM) in Preventing SARS-CoV2 Infection, Chennai, Tamil Nadu, India, 2021,” and published in Vaccines (June 17 ,2022), 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 the population, hence generating data closer to a 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 healthcare 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 COVID-19 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+) was picking up rapidly and by May 22, 2021, about 20 per cent of individuals ≥45 years 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.

The 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. 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 studies at the population level in the context of changing variants and newer vaccines and boosters,” Dr Kaur noted.

The disease surveillance (including hospitalisation) and vaccination programme 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 the disease surveillance and vaccination databases at the national and state levels to enable regular, in-depth, real-time analysis of vaccine effectiveness.

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