Study: Covid-19 vaccine is over 90% effective at preventing deaths from Delta

Reviewed by Emily Henderson, B.Sc.Oct 21 2021

Vaccination is over 90 per cent effective at preventing deaths from the Delta variant of Covid-19, according to the first country-level data on mortality.

The Pfizer-BioNTech vaccine is 90 per cent effective and the Oxford-AstraZeneca vaccine 91 per cent effective in preventing deaths in people who have been double vaccinated, but who have tested positive for coronavirus in the community, research shows.

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, which is now the dominant form of Covid-19 in the UK and many other countries.

Researchers analyzed data from 5.4 million people in Scotland between 1 April and 27 September 2021.

During this period, 115,000 people tested positive for Covid-19 through a PCR test conducted in the community, rather than in hospital, and there were 201 deaths recorded due to the virus.

The Moderna vaccine is also available in Scotland and no deaths have been recorded in those who have been double vaccinated with it. Consequently, it has not been possible to estimate its effectiveness in preventing death, researchers said.

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 research team from Universities of Edinburgh and Strathclyde and Public Health Scotland analyzed a dataset as part of the EAVE II project, which uses anonymized linked patient data to track the pandemic and the vaccine roll out in real time.

The results are published as a letter in the New England Journal of Medicine.

The researchers say to increase confidence in these early findings, the research needs to be repeated in other countries and settings, and with longer follow-up time after full vaccination.

The team say 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.

With the Delta variant now the dominant strain in many places worldwide and posing a higher risk of hospitalization 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.

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."

Professor Aziz Sheikh, Director, University of Edinburgh's Usher Institute and EAVE II Study Lead

Professor Chris Robertson, University of Strathclyde and Public Health Scotland, said: "This study shows the value of carrying out analyses of routine healthcare data available in near real-time.

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

The study was funded by the Medical Research Council, UK Research and Innovation Industrial Strategy Challenge Fund, the National Institute for Health Research and Health Data Research UK (HDR UK), and was supported by the Scottish Government.

Additional support was provided through the Scottish Government Director-General Health and Social Care, and the UKRI COVID-19 National Core Studies Data and Connectivity program led by HDR UK.