Vaccine Efficacy against the Delta Variant in Scotland
October 2021: Research published in the New England Journal of Medicine estimates the level of protection that vaccines give against deaths from COVID-19 infection with the Delta variant.
Summary in Plain English
The Delta variant became the most common type of coronavirus (SARS-CoV-2) in Scotland on 19 May 2021. It is more infectious and more likely to cause severe disease than other variants, so was labelled as a ‘variant of concern’ (VOC).
Why is this research important?
Variants of concern can have a big impact on pandemic restrictions and people’s health, especially if they evolve in a way that makes existing vaccines less effective.
We showed previously that the Pfizer-BioNTech (BNT162b2) and Oxford-AstraZeneca (ChAdOx1) vaccines are initially effective against COVID-19 infection and hospital admissions caused by the Delta variant.
Because of the effectiveness of the vaccines and restrictions, there were – thankfully – very few COVID-19 deaths in the time period studied.
However, it is still important to understand how much protection the vaccines offer against COVID-19 deaths, particularly now that the Delta variant is the most common type in the UK and people are mixing more.
What data did we use?
We used healthcare data from around 99% of the Scottish population to answer questions about vaccine effectiveness.
This data is accessed through the EAVE II study cohort. We looked at a group of over 1.5 million people aged 16 and over who had PCR (‘Polymerase Chain Reaction’) tests between 1 April and 16 August 2021 in the community. From this group, nearly 115,000 people tested positive. We monitored the people who tested positive until 27 September 2021.
Community-based PCR tests can be used as a reliable test for whether someone has been infected with the Delta variant or not.
We defined COVID-19 deaths 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.
What were the results?
From 1 April to 27 September 2021, there were 201 COVID-19 deaths in the group studied.
In the 16-39 age bracket, 17 unvaccinated people died and no fully vaccinated people died.
The Pfizer-BioNTech vaccine was 95% effective in 40-59 year olds and 87% effective in people 60 and over. The Oxford-AstraZeneca vaccine was 88% effective in 40-59 year olds and 90% effective in people aged 60 or older.
In people of all ages who had been double-vaccinated at least two weeks before a positive PCR test, we found that the vaccines offer good protection against COVID-19 deaths caused by the Delta variant:
- Pfizer-BioNTech vaccine was 90% effective
- Oxford-AstraZeneca vaccine was 91% effective
So far, there have been no COVID-19 deaths following the smaller number of Moderna vaccinations given more recently in Scotland.
What is next?
These results provide vital data about how well the vaccines used in the UK protect against COVID-19 deaths caused by the Delta variant. Both vaccines provide strong protection, which varies slightly by age group.
However, the results are only based on people who test positive for COVID-19 in the community, rather than the whole population. This means that the results should be treated with caution.
We will continue to monitor vaccine safety and effectiveness in Scotland as young people are vaccinated, as more people receive Moderna, third or vaccine booster doses are given, or as new variants of coronavirus emerge.
This plain English summary and infographic were created with the support and feedback of the EAVE II Public Advisory Group (PAG). This summary in particular was reviewed by Emily L.
To learn more about the PAG, see: Our EAVE II Public Advisory Group (PAG) | The University of Edinburgh