SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness

June 2021: The Delta variant of COVID-19 is associated with approximately double the risk of hospitalisation compared with the Alpha variant, but vaccine continues to protect.

Plain English summary

The Delta variant, also known as B1.617.2, was first found in India. It replaced the Alpha or ‘Kent’ variant to become the most common strain of SARS-CoV-2 in Scotland on 19 May 2021.

It is known as a variant of concern (VOC), which means that it meets one or more of these criteria:

• The variant causes an increase in community transmission
• The variant makes COVID-19 symptoms change or become more severe
• The variant makes measures like vaccines, medication, diagnostic tests, social distancing or wearing masks less effective.

Find out more about VOCs [World Health Organisation]

Why did we carry out this study?

Variants of concern can have a major impact on pandemic restrictions and burdens on the National Health Service. It is important to establish whether existing measures like vaccines and social restrictions are still effective against new variants as early as possible.

We wanted to investigate how much protection the Oxford-AstraZeneca and Pfizer-BioNTech vaccines offer against the new Delta variant, compared to the Alpha (or Kent) variant. We also wanted to understand if the Delta variant puts people at higher risk of being admitted to hospital after a positive COVID test.

To do this, we used data from the EAVE II platform, which holds anonymised healthcare information for 99% of the Scottish population in a secure database.

How can we tell the SARS-CoV-2 variants apart?

PCR tests are used to tell whether a person has a SARS-CoV-2 infection. UK PCR tests can be used to see if swab samples contain the S gene – a section of genetic code that appears in some SARS-CoV-2 virus samples, but not others.

From 1 April to 28 May 2021 in Scotland, data showed that 97% of S gene-positive samples were the Delta variant, and also that 99% of Delta variants had the S gene.

Together, this means that an S gene-positive PCR test could be used as a very reliable indicator that a patient had been infected with the Delta rather than Alpha variant.

What definitions did we use?

We defined COVID-19 hospital admission as a patient being admitted to hospital within 14 days of a positive PCR test for SARS-CoV-2.

People who became infected during a hospital stay, or only tested positive after 3 or more days in hospital, were excluded from the study. This allowed us to focus on the effects of community transmission.

The analysis covers the period from 1 April to 6 June 2021. During this time, the number of people who had been given the first dose of a vaccine increased from 45 to 60%. The number of second doses increased from 8 to 39%.

What did we find in this study?

Effect of the Delta variant on hospitalisation

We found that being infected with the Delta variant roughly doubled a person’s risk of being admitted to hospital, when compared to S gene-negative cases. This comparison took into account age, sex at birth, deprivation level, time and health history.

People with multiple health problems were more likely to be hospitalised. However, 7 in 10 Delta variant cases were in people with no relevant underlying health conditions.

A higher proportion of Delta cases are in children and young adults, and also in the more affluent, compared to Alpha cases.

Impact of the Delta variant on vaccine effectiveness

Our data analysis shows that the vaccines are still effective in reducing hospital admissions and infections caused by the Delta variant.

However, the level of protection against infection given by the two most common UK vaccines is reduced when compared to the Alpha variant of SARS-CoV-2.  Strong protection against infection was only seen in community cases after the second dose.

In this group, both vaccines were found to be 13% less effective against infection with the Delta variant compared to the Alpha variant.

The Pfizer-BioNTech vaccine saw a drop in effectiveness from 92% to 79%.

The protection reduced from 73% to 60% for the Oxford-AstraZeneca vaccine. This vaccine may take longer to generate immunity against the virus, which may explain the lower protection given in the period studied.

Strong protective effects against the Delta variant from either vaccine for hospital admission were not seen until at least 28 days after the first dose.

What is next?

This research provides vital, recent data on the impact of the Delta variant on health and vaccine effectiveness. Because it is an early observational study, we recommend that the research should be repeated in other countries and settings to give greater confidence in the results. There were not enough hospitalisation cases to compare the two vaccines fully.

We plan to expand the data that we monitor if and when new viral strains and vaccines appear.

Over a matter of weeks, the Delta variant has become the dominant strain of SARS-CoV-2 in Scotland. It is unfortunately associated with increased risk of hospitalisation from COVID-19.

Whilst possibly not as effective as against other variants, two doses of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines still offer substantial protection against the risk of infection and hospitalisation. It is therefore crucially important that, when offered second doses, people take these up both to protect themselves and to reduce household and community transmission.

These results provide early encouragement that two doses of either Pfizer-BioNTech or Oxford-AstraZeneca vaccines significantly reduce the risk of infection against both the Alpha or new Delta variants. They also show the vaccines offer protection against the risk of hospitalisation with the new Delta variant. Though no vaccine can be 100% protective, they provide the best protection against COVID-19 and it remains important to get both doses when offered.

It is important to recognize that these are preliminary results using rapidly accessible data.  A fuller understanding will come when the results presented here are combined with similar analyses from other data sets in the UK.

This is another outstanding example of why rapid, safe and secure linkage of health data across entire care journeys, including information from GPs, vaccinations, viral genetics and hospital admissions data, is essential for research that makes a difference to people’s lives. These results will inform decision making internationally. HDR UK and the UKRI National Core Studies are working in partnership with the EAVE II team and the public to accelerate more trustworthy research that will be essential to this and future pandemics.

Read the letter

SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness 

Scottish government statement

The First Minister released a statement about this research on 15 June 2021.

Scotland’s First Minister Statement in the Scottish Parliament | BBC News Scotland

Ms Sturgeon says the early data is encouraging, but further analysis is needed to understand the Delta variant.

The first minister says a study published by Edinburgh University yesterday was "instructive".

It suggested that the Delta variant is associated with a higher risk of hospitalisation - but on the other hand, it shows double vaccination provides a high level of protection.

“There is extremely strong protection now with two doses of vaccine”, the First Minister says.

Further information

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

The study was funded by the Medical Research Council, UK Research and Innovation Industrial Strategy Challenge Fund 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 programme led by HDR UK.

Cite as

Sheikh, A., McMenamin, J., Taylor, B., Robertson, C. SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness. (June 14, 2021). https://doi.org/10.1016/S0140-6736(21)01358-1 

Note

This plain English summary and infographic were created with the support and feedback of the EAVE II Patient Advisory Group (PAG). This summary in particular was reviewed by David W.

To learn more about the PAG, see: Our EAVE II Patient Advisory Group (PAG) | The University of Edinburgh