Coronavirus: Covishield vaccine reduces breakthrough COVID-19 infections by 93%, shows study

The study looked at a total of 15,95,630 participants having an average age of 27.6 years

Covishield COVID-19 vaccine: In what can be seen as a positive development, an interim study that looked at 1.59 million or 15.9 lakh healthcare and frontline Indian armed forces workers has found that Serum Institute of India-manufactured coronavirus vaccine Covishield led to a whopping 93% reduction in breakthrough COVID-19 infections. The study was one of the largest to be conducted anywhere across the globe, according to a report in IE. Covishield is the India variant of the coronavirus vaccine developed by Oxford University and AstraZeneca, and it is being used extensively in the mass immunisation drive being carried out in the country.

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The VIN-WIN cohort study’s results have been published in Medical Journal Armed Forces India’s special issue this week, and it has brought to focus, again, the huge benefits that vaccination can have in terms of reducing the breakthrough infections and deaths due to COVID-19.

The report cited study’s corresponding author Air Cmde Subramanian Shankar as saying that other studies usually have a sample size of less than 1 million (10 lakh) participants, which is why the researchers of this study believe that this is among the largest – if not the largest – studies to be conducted across the globe to look at the effectiveness of vaccination.

Since healthcare workers and frontline workers of the Indian armed forces were among the first priority group in India to get the vaccine doses, and now, the study has presented an interim analysis of the estimates regarding vaccine effectiveness in 1.59 people who had received the vaccine till May 30.

The study looked at a total of 15,95,630 participants having an average age of 27.6 years, of whom, 99% were males, and till May 30, 95.4% were partially vaccinated while 82.2% were fully vaccinated, the report added. Their data over 135 days was analysed. Three compartments were made – unvaccinated (UV), partially vaccinated (PV) and fully vaccinated (FV). The UV compartment comprised 106.6 million person-days, while this was 46.7 million for PV and 58.7 million for FV. In the UV group, the number of breakthrough cases were found to be 10,061, while this was 1,159 for PV and 2,512 for FV group, and the deaths in these three groups were 37, 16 and 7 respectively. Accordingly, the corrected vaccine effectiveness came to be 91.8% to 94.9% against infections.

For this purpose, the study made use of anonymised COVID-19 data that already existed in the Armed Forces Health Surveillance system, and since each individual was in one of the three groups for a varying time period, in order to standardise, the study measured the population at risk in person days – which means that for instance, 100 person days could be either one person for 100 days or 10 persons for 10 days each.