Coronavirus (COVID-19) Infection Survey, UK: 16 March 2023

The following points are for the week ending 7 March 2023 for England, Wales and Northern Ireland, and the week ending 6 March 2023 for Scotland.

• The estimated percentage of people testing positive for coronavirus (COVID-19) decreased in Scotland, and the trends were uncertain in England, Wales and Northern Ireland.

• In England, the estimated number of people testing positive for COVID-19 was 1,322,000 (95% credible interval: 1,241,500 to 1,410,100), equating to 2.36% of the population, or around 1 in 40 people.

• In Wales, the estimated number of people testing positive for COVID-19 was 68,200 (95% credible interval: 52,300 to 85,500), equating to 2.21% of the population, or around 1 in 45 people.

• In Northern Ireland, the estimated number of people testing positive for COVID-19 was 26,600 (95% credible interval: 15,600 to 40,700), equating to 1.45% of the population, or around 1 in 70 people.

• In Scotland, the estimated number of people testing positive for COVID-19 was 105,100 (95% credible interval: 82,600 to 130,600), equating to 2.00% of the population, or around 1 in 50 people.

• In England, the estimated percentage of people testing positive for COVID-19 increased in the North West and Yorkshire and The Humber, decreased in the East of England, East Midlands and London, and the trends were uncertain in the North East, West Midlands, South East and South West.

• In England, the estimated percentage of people testing positive for COVID-19 continued to increase for those aged 70 years and over, decreased for those in school Year 12 to aged 24 years and those aged 35 to 49 years, and the trends were uncertain for the remaining age groups.

This week's bulletin has been released a day earlier to accommodate the 17 March 2023 bank holiday in Northern Ireland.

We will be pausing Coronavirus (COVID-19) Infection Survey data collection from mid-March, and as a result the final weekly publication will be published on 24 March 2023. As the UK Health Security Agency (UKHSA) works to confirm its approach to surveillance, the Office for National Statistics (ONS) plans to work with existing participants to continue gathering valuable insight into the experiences of COVID-19, long COVID and other respiratory infections, details of which will be announced in due course. We thank our participants for their continued support.

Figure 1: The percentage of people testing positive for coronavirus (COVID-19) decreased in Scotland, and the trends were uncertain in England, Wales and Northern Ireland, in the most recent week

Estimated percentage of the population testing positive for COVID-19 on nose and throat swabs, UK, 27 February 2022 to 7 March 2023

Notes:

1. Modelled results are provisional and subject to revision.

2. These statistics refer to infections occurring in private households. The figures exclude infections reported in hospitals, care homes and/or other communal establishments.

3. Official reported estimates are plotted at a reference point believed to be most representative of the given week.

4. The official estimate presents the best estimate at that point in time. Modelled estimates are used to calculate the official reported estimate. The model smooths the series to understand the trend and is revised each week to incorporate new test results, providing the best indication of trend over time.

5. Official estimates are displayed over a rolling year up to the most recent week. The full time series of our official estimates from 27 April 2020 onwards are available in our Coronavirus (COVID-19) Infection Survey datasets.

6. There is a higher degree of uncertainty in our estimates for Wales, Northern Ireland, and Scotland, compared with England. This is shown by wider credible intervals.

7. The reference week is 1 to 7 March 2023 for England, Wales and Northern Ireland, and 28 February to 6 March 2023 for Scotland.

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Age groups for children and young people

• "Aged 2 years to school Year 6" includes children in primary school and below.

• "School Year 7 to school Year 11" includes children in secondary school.

• "School Year 12 to those aged 24 years" includes young adults who may be in further or higher education.

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. A wider interval indicates more uncertainty in the estimate. Overlapping credible intervals indicate that there may not be a true difference between two estimates. For more information, see our methodology page on statistical uncertainty.

Cycle threshold (Ct) values

The strength of a positive coronavirus (COVID-19) test is determined by how quickly the virus is detected, measured by a cycle threshold (Ct) value. The lower the Ct value, the higher the viral load and stronger the positive test. Positive results with a high Ct value can be seen in the early stages of infection when virus levels are rising, or late in the infection, when the risk of transmission is low.

Whole genome sequencing

Swabs that are positive on a PCR test for COVID-19 with a Ct value less than 30 are additionally sent for genomic sequencing. A detailed investigation is undertaken to work out the specific order of the letters that make up the genetic material of the virus in the sample. Where we can identify at least 50% of the genetic code, we can identify the COVID-19 variant present through comparisons with the genetic sequences of known variants. Currently, the variants under surveillance in the UK are Omicron, including sub-lineages BA.2 and BA.5 and their sub-lineages.

Reference dates

We aim to provide the estimates of positivity rate (the percentage of people who test positive) that are most timely and most representative of each week. In addition, to improve stability in our modelling while maintaining relative timeliness of our estimates, we report our official estimates based on the midpoint of the reference week.

This week, the reference week is 1 to 7 March 2023 for England, Wales and Northern Ireland and the reference day is 4 March 2023, and the reference week is 28 February to 6 March 2023 for Scotland and the reference day is 3 March 2023. More information on reference weeks and days can be found in the Measuring the data section of our Coronavirus (COVID-19) Infection Survey, UK: 10 March 2023 bulletin.

Additional COVID-19 Infection Survey data

Our full Coronavirus (COVID-19) Infection Survey datasets for England, Wales, Northern Ireland, Scotland and our Technical dataset are available. These datasets include our monthly incidence, sub-regional and single year of age analysis.

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.

Remote data collection

The Office for National Statistics (ONS) Coronavirus (COVID-19) Infection Survey has moved from collecting data and samples through home visits by a study worker to a more flexible approach for participants. We have introduced an online questionnaire and swab and blood samples are returned through the post (or by courier for some participants). Further information on what these changes mean and how the survey will continue to be valuable can be found in our recent blog post: The COVID-19 Infection Survey is changing.

There were minimal differences between estimates of swab positivity produced from remote data collection methods, compared with data collected by study worker home visits. New data presented in our Coronavirus (COVID-19) Infection Survey, UK: 19 August 2022 bulletin were based on a combination of data collected remotely and by study worker home visits. New data presented from our Coronavirus (COVID-19) Infection Survey, UK: 26 August 2022 bulletin onwards were collected by remote data collection only. Further information on the effects of the change in data collection method can be found in our Quality Report: August 2022 and Quality Report: December 2022.

Other Coronavirus Infection Survey (CIS) analysis and studies

This study provides the main measure of coronavirus infection in the UK. Other sources have provided data during previous stages of the pandemic. For information on other studies see Section 4: Quality characteristics of the Coronavirus (COVID-19) Infection Survey (coherence and comparability) of the Coronavirus (COVID-19) Infection Survey: quality and methodology information (QMI), revised 20 January 2023.

Quality

More quality and methodology information on strengths, limitations, appropriate uses, and how the data were created is available in our Coronavirus (COVID-19) Infection Survey: methods and further information article and the Coronavirus (COVID-19) Infection Survey: quality and methodology information (QMI).