COVID-19 vaccine effectiveness against symptomatic SARS-CoV-2 infection and severe COVID-19 outcomes from Delta AY.4.2

Summary in plain English

In July 2021 a new sub-variant of coronavirus (SARS-CoV-2) was detected in the UK. It was labelled as AY4.2 or ‘Delta plus’, because it evolved from the Delta variant.

The ‘Delta plus’ variant made up 10-11% of cases in the UK by October 2021 and was listed as ‘under investigation’ by the UK Health Security Agency in the same month.

Find out more about the UK Health Security Agency

Why did we carry out this research?

We wanted to understand how effective the vaccines currently available in the UK were against the Delta plus variant. This includes their ability to protect people against symptomatic COVID-19, as well as COVID-19 hospital admission and death.

It is important to understand the impact of any new variants on public health measures like vaccines, as they can become a common variant very quickly.

The Delta and Delta plus variants were replaced rapidly in the UK by another new variant, Omicron, in November 2021. This research is the only study at a national population scale to look at the effectiveness of vaccines against the Delta plus variant.

What data did we use?

To look at vaccine effectiveness, we used data held in the Early Pandemic Evaluation and Enhanced Surveillance (EAVE II) platform. This includes information about people’s GP, hospital and death records, COVID-19 testing and viral variant data, and vaccination, for 99% of the Scottish population.

Find out more about EAVE II

We looked at people who tested positive for SARS-CoV-2 between 8 June and 25 October 2021. This includes vaccinated and unvaccinated people.

Find out more about COVID-19 vaccines in the UK [NHS Inform Scotland]

We used two types of statistical analysis to look at how effective vaccines were in protecting people against symptomatic COVID-19 disease, and against hospital admission and death.

To look at symptomatic disease, we matched people who tested positive on a PCR test in the community, with similar people who tested negative. This helps to account for the fact that a person’s vaccination status and the likelihood of them getting a PCR test are linked.

For hospital admission and deaths, we only looked at people who tested positive for SARS-CoV-2 in the community – rather than in hospital – and who had their PCR test swab sequenced to detect the viral variant.

We defined hospital admission as people admitted to hospital in an emergency within 14 days of a positive test. We defined COVID-19 deaths as people who died within 28 days of a positive PCR test, or with COVID-19 recorded on their death certificate.

What did we find?

We found that people who had two doses of a vaccine were 73% less likely than unvaccinated people to have symptomatic COVID-19 caused by the Delta plus variant.

Double-vaccinated people were also 87% less likely to die or be admitted to hospital in an emergency with COVID-19 than unvaccinated people.

We found that the risk of COVID-19 hospital admission and death for unvaccinated people was 1-3 times higher following Delta plus infections than for the Delta variant.

Why is this important?

In this study, we found that the Delta plus variant was linked to a higher risk of emergency COVID-19 hospital admission and death for unvaccinated people, compared to Delta.

We also found that the vaccines currently available in the UK give people good protection against both symptomatic disease, and hospital admission and death, caused by the Delta plus variant.

This research is one of the few studies to look at vaccine effectiveness against Delta plus in real world settings.

In the future, we can use the established methods described above to quickly look at the impact of any new variants on vaccine effectiveness and COVID-19 disease.

Note

This summary was written by EAVE II's Patient and Public Involvement Coordinator Dr Lana Woolford, with contributions from Patient Advisory Group (PAG) members Eve S and Peter M, in consultation with EAVE II analysts.

Find out more about our PAG