1. Main points
During this period of high infections, we have decided to publish our headline results two days early. This means that the latest estimates on infection levels are available at their earliest opportunity and further breakdowns for the same period and a longer time series will be published on Fridays. These early estimates are provisional and are subject to change as we receive more data, but they have undergone sufficient quality assurance to ensure that they are based upon an acceptable number of test results received up to the end of the reference week. This week, we are publishing estimates for the week ending 31 December, based on a reference date of 28 December to account for anticipated additional test results for the last few days.
Today, we have published new data that show in the week ending 31 December 2021:
In England, the percentage of people testing positive for coronavirus (COVID-19) continued to increase; we estimate that 3,270,800 people in England had COVID-19 (95% credible interval: 3,163,500 to 3,377,500), equating to around 1 in 15 people.
In Wales, the percentage of people testing positive for COVID-19 continued to increase; we estimate that 157,900 people in Wales had COVID-19 (95% credible interval: 138,900 to 179,600), equating to around 1 in 20 people.
In Northern Ireland, the percentage of people testing positive for COVID-19 continued to increase; we estimate that 72,900 people in Northern Ireland had COVID-19 (95% credible interval: 56,800 to 90,100), equating to around 1 in 25 people.
In Scotland, the percentage of people testing positive for COVID-19 continued to increase; we estimate that 238,000 people in Scotland had COVID-19 (95% credible interval: 209,300 to 268,000), equating to around 1 in 20 people.
In England, COVID-19 infections continued to increase across all age groups and were highest among those in school Year 12 to age 24 years.
In the last few days of 2021, the trend in the percentage testing positive was uncertain for those in London who are secondary school ages and those aged 25 to 49 years, which may mean that infections are no longer increasing among these ages in London, but it is currently too early to suggest if this is a continuing change in trend.
COVID-19 infections continued to increase across all regions of England, with the highest percentage testing positive in London (1 in 10) and the lowest in the South West of England (1 in 30); there were some early signs in the last few days of 2021 that infections may no longer be increasing in London, but it is currently too early to suggest if this is a continuing change in trend.
COVID-19 infections compatible with the Omicron variant continued to increase rapidly across England, Wales, Northern Ireland and Scotland, and Omicron is now the most common variant across all UK countries.
Figure 1: COVID-19 infections compatible with the Omicron variant continued to increase rapidly across England, Wales Northern Ireland and Scotland in the week ending 31 December 2021
Modelled percentage of positive cases compatible with the Delta variant, and compatible with the Omicron variant, based on nose and throat swabs, daily, from 20 November to 31 December 2021, UK
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Notes:
- All results are provisional and subject to revision.
- These statistics refer to infections occurring in private households, and exclude infections reported in hospitals, care homes and/or other communal establishments.
- Omicron variant-compatible positives are defined as those that are positive on the ORF1ab-gene and N-gene, but not the S-gene. Delta variant-compatible positives will mostly have a gene pattern ORF1ab+N+S (or occasionally S+ORF1ab and S+N), and so in this analysis are defined as those that are positive on the ORF1ab, N-gene and S-gene, as well as gene patterns N+S and ORF1ab+S.
- Data should be treated with caution. Not all cases positive on the S-gene will be the Delta variant, but some cases with pattern ORF1ab+N will also be the Delta variant where the S-gene was not detected for other reasons, such as low viral load.
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Back to table of contents3. Glossary
Credible interval
A credible interval gives an indication of the uncertainty of an estimate from data analysis. The 95% credible intervals are calculated so that there is a 95% probability of the true value lying in the interval.
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4. Measuring the data
Reference dates
This week, the reference week is 25 to 31 December 2021 and the reference day is Tuesday 28 December 2021. More information on reference weeks and days can be found in the Measuring the data section of our Coronavirus (COVID-19) Infection Survey, UK: 23 December 2021 bulletin.
Data for a longer time series
A longer time series from earlier data can be found in our usual weekly Coronavirus (COVID-19) Infection Survey datasets for England, Wales, Northern Ireland and Scotland.
Survey fieldwork
Survey fieldwork for the pilot study began in England on 26 April 2020. Fieldwork began on 29 June 2020 in Wales, 26 July 2020 in Northern Ireland, and 21 September 2020 in Scotland.
Other Coronavirus Infection Survey (CIS) analysis and studies
This study is one of a number of studies that look to provide information around the coronavirus pandemic within the UK. For information on other studies see Section 11: Measuring the data in our previous bulletin, published 30 April 2021.
Quality
More quality and methodology information on strengths, limitations, appropriate uses, and how the data were created is available in our methods article and the Coronavirus (COVID-19) Infection Survey QMI.
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