Two doses of Covishield and Pfizer COVID-19 vaccines may be 90 per cent effective at preventing deaths from the Delta variant of the SARS-CoV-2 virus, according to a study published in the New England Journal of Medicine on 21 October.

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The study, using data from the Scotland-wide EAVE II COVID-19 surveillance platform, is the first to show across an entire country how effective vaccines are at preventing death from the Delta variant, the dominant form of the virus in many other countries. The research team from the Universities of Edinburgh and Strathclyde and Public Health Scotland analysed data from 5.4 million people in Scotland between April 1 and September 27, 2021.

During this period, 115,000 people tested positive for COVID-19 through a PCR test conducted in the community, rather than in the hospital, and there were 201 deaths recorded due to the virus. The study found that the Pfizer-BioNTech vaccine is 90 per cent effective and the Oxford-AstraZeneca vaccine, known as Covishield in India, is 91 per cent effective in preventing deaths in people who have been double vaccinated, but who have tested positive for coronavirus in the community.

"With the Delta variant now the dominant strain in many places worldwide and posing a higher risk of hospitalisation than previous variants seen in the UK, it is reassuring to see that vaccination offers such high protection from death very shortly after the second dose," said Professor Aziz Sheikh, Director of the University of Edinburgh's Usher Institute, and EAVE II study lead.

"If you still have not taken up your offer to be vaccinated, I would encourage you to do so based on the clear benefits it offers," Sheikh said. The researchers defined death from COVID-19 as anyone who died within 28 days of a positive PCR test, or with COVID-19 recorded as a cause of death on their death certificate.

The study analysed a dataset as part of the EAVE II project, which uses anonymised linked patient data to track the pandemic and the vaccine rollout in real-time. The researchers said to increase confidence in these early findings, the study needs to be repeated in other countries and settings, and with longer follow-up time after full vaccination.

They noted that because of the observational nature of the study, data about vaccine effectiveness should be interpreted with caution and it is not possible to make a direct comparison between both vaccines. "Our findings are encouraging in showing that the vaccine remains an effective measure in protecting both ourselves and others from death from the most dominant variant of COVID-19," said Professor Chris Robertson, from the University of Strathclyde and Public Health Scotland.

"It is very important to validate these early results in other settings and with a longer follow-up study," Robertson added.