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Vaccine effectiveness and severity of Omicron BA.5 variant on COVID-19 outcomes in Scotland

Research published in The Lancet Regional Health - Europe investigates Omicron BA.5 variant risk and vaccine protection on severe COVID-19 outcomes in Scotland.

Severity of Omicron BA.5 variant and protective effect of vaccination: national cohort and matched analyses in Scotland

Robertson, C; Sheikh, A & Kerr, S

The Lancet Regional Health - Europe

Published on: 14 April 2023

Available online at: https://doi.org/10.1016/j.lanepe.2023.100638

Summary in plain English

Omicron is a variant of COVID-19. In January 2022, a sub-variant (BA.5) was discovered in South Africa. It was labelled as a “variant of concern” by the UK Health and Security Agency on 18 May 2022. Within a month thereafter, it had become the most common strain in the UK. Researchers in the UK and globally compared BA.5 to previous Omicron strains. It was established BA.5 is linked to an increased risk of people being admitted to hospital. However, vaccine effectiveness was not reduced.

Why did we carry out this work?

We wanted to analyse the severity of the BA.5 variant to understand risk of infection and serious COVID-19 outcomes. This may include vulnerable people admitted to hospital or those who are dying from disease. The purpose of this research is to help shape future health policy. This may lead to more effective COVID-19 intervention for those who need it the most.

What data did we use?

Our study was completed from 1 April 2022 – 30 September 2022. We used health data held on our EAVE platform. The data located therein is comprised of 5.4 million records of those people who have GP records. This national data set was representative of 99% of the Scottish population. We compared the two Omicron strains BA.5 and BA.2. At the time of the study BA.2 was the most common strain in the UK before BA 5 established itself in the UK. To measure severity, we investigated the numbers of people admitted to hospital with COVID-19 and those who died. We classified certain types of data as:

  • COVID-19 hospitalisation: a person who has been admitted to hospital with a diagnosis of COVID-19 and had a positive test within 28 days prior or 2 days after being admitted.
  • COVID-19 death: a person who has passed away with COVID-19 listed as a cause of death. This information is on their death certificate within 56 days from the date of their positive test.
  • Vaccination status: a person who had received a COVID-19 vaccine at the time when a positive RT-PCR test was taken.

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Statistical analysis techniques were   adopted to identify those people who were tested for both variants but were not admitted to hospital. The following characteristics were used as predictors of severe outcomes:

  • Type of virus
  • Sex
  • Number of risk groups
  • A person on a shielding list
  • Vaccine history
  • Time period if the person had previously tested positive
  • Age/calendar days from the beginning of the study
  • Testing location
  • Those who may have less immunity
  • Socio-economic status.

Further statistical analysis was completed for COVID-19 hospital admission. We matched BA5 and BA2 cases by date, location and age based both variant’s case numbers, and compared risk of hospitalisation. Results showed there is a higher risk of hospitalisation and death of BA.5 compared to BA.2 in older age groups and children aged 0-11 with the BA.5 variant.

What did we find?

Overall pattern

We found vaccines offer protection against both the BA.2 and BA.5 variants together with the risk of severe COVID-19 outcomes including hospitalisation.

Vaccine effectiveness

The vaccine offered good protection for up to 26 weeks after people received their third dose and for those who were previously infected.

Impact on hospital admissions

The analysis provides evidence that the BA.5 variant carries an increased risk of a COVID admission to hospital compared to BA.2.

Impact on mortality

The data suggests the BA.5 variant may carry more risk of death compared to BA.2. However, more evidence is needed to support this finding.

Why is this important?

There are few longer-term studies on risk of infection and outcomes of BA.5. We used national data from Scotland to study the risk of BA.5 infection and serious COVID-19 outcomes. This study showed the BA.5 variant increases the risk of COVID-19 hospitalisation compared to the BA.2 variant. A higher risk of death can be argued, however, research shows vaccines reduce the risk of these outcomes.

In Scotland, mass testing ended on 18 April 2022. This may have contributed to under-recorded rates of people admitted to hospital or dying. In addition, there is a possibility of factors that were not able to be analysed. Lastly, different variants were identified in positive tests. Due to the nature of this process, there may have been bias. 


This summary was written by EAVE II's Patient and Public Involvement Officer Anna Crawford, with contributions from Patient Advisory Group (PAG) members David W and Carrol L, as well as feedback from the EAVE II analysis team.

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