Coronavirus (covid-19) infection survey, Northern Ireland: weekly report

The Department of Health today published the next in the series of weekly results from its COVID-19 Infection Survey (CIS). The findings set out in this report relate to modelled positivity estimates for NI for the week up to the 29 January 2022. The aims of the CIS are to estimate how many people have the infection and the number of new cases that occur over a given time as well as estimating how many people have developed antibodies to COVID-19.

The survey over time will help track the extent of infection and transmission of COVID-19 among people in the community population (those in private residential households).

Key Findings

To ensure our latest estimates on positivity are available at the earliest opportunity during this period of high infections, we published our headline results on Wednesday. The analysis in this bulletin provides further breakdowns for the same period and a longer data time series.

Due to the relatively small number of tests and positive swab results within our sample, credible intervals are wide and therefore results should be interpreted with caution.

• during the most recent week of the study (23 January – 29 January), it is estimated that 136,300 people in Northern Ireland had COVID-19 (95% credible interval: 118,200 to 155,200). 
• this equates to 7.43% of the population (95% credible interval: 6.44% to 8.46%) or around 1 in 15 people (95% credible interval 1 in 15 to 1 in 10).
• modelling suggests the percentage of people testing positive increased in the week ending 29 January in Northern Ireland.
• in the latest six-week period, there were 15,167 swab tests taken in total from 11,565 participants. Of these, 682 participants tested positive from 520 different households.
• in the latest two-week period, of the 5,472 participants in the study, 301 tested positive from 225 households.
• the percentage testing positive increased across all ages in Northern Ireland.
• since the end of December, infections compatible with the Omicron BA.1 variant have been the most common in all four UK countries. The main variant analysis shows that in Northern Ireland, there was a notable increase in the percentage of people testing positive not compatible with Omicron BA.1 in the week ending 29 January 2022. This group of positives will include Omicron BA.2 and Delta cases; the majority of recent cases will be Omicron BA.2 based on genetic sequencing (see below for more information on the variant analysis undertaken).

Variant analysis

The World Health Organization (WHO) have defined names for Variants of Concern. These are variants that the UK government has under surveillance. You can find out more in the SARS-CoV-2 variants of concern and variants under investigation in England briefing document (PDF, 2.51MB).

UK Variants of Concern:

• Alpha: B.1.1.7
• Beta: B.1.351
• Gamma: P.1
• Delta: B.1.617.2 and its genetic descendants
• Omicron: B.1.1.529 (which includes sublineages BA.1, BA.2 and BA.3)

The Omicron variant currently dominant in the UK is BA.1. This variant has changes in one of the three genes that the coronavirus swab used in the survey tests detects, known as the S-gene. This means the S-gene is no longer detected by the current test. When there is a high viral load (for example, when a person is most infectious) absence of the S-gene in combination with the presence of the other two genes (ORF1ab and N-genes) is a reliable indicator of this Omicron variant (BA.1). However, as the viral load decreases (for example, if someone is near the end of their recovery from the infection), the absence of the S-gene is a less reliable indicator of this Omicron variant. The sub-variant Omicron BA1.1 also mostly has gene pattern ORF1ab + N. Therefore, gene pattern matching used in the main variant analysis cannot distinguish between Omicron BA.1 and Omicron BA1.1.

In contrast, the Omicron sub-variant BA.2 does not have changes in the S gene, and therefore the detection of all three genes, or the S-gene and either ORF1ab or N is usually a reliable indicator of this sub-variant of Omicron.  ​ Delta also does not have changes in the S-gene, and therefore has identical gene patterns to Omicron BA.2. This means that gene pattern matching cannot distinguish between Omicron BA.2 cases and Delta cases. For this reason, cases with gene patterns ORF1ab + N + S, ORF1ab + S and N + S are labelled as ‘not compatible with Omicron BA.1’ in the main variant analysis. The genome sequencing analysis suggests that a clear majority of cases with these gene patterns are now Omicron BA.2, with relatively few being Delta. For this reason, 'not compatible with Omicron BA.1' estimates are now likely to mostly reflect trends in BA.2, although Delta may still be having a very small impact.

More information on how variants from positive tests on the survey are measured can be found in the ONS Understanding COVID-19 Variants blog and in the methodology article.

Notes to editors: 

1. The Department of Health has been working along with the Public Health Agency, Northern Ireland Statistics and Research Agency and the Office for National Statistics (and its various survey partners) to extend the COVID-19 Infection Survey to Northern Ireland. Fieldwork in Northern Ireland began on 27 July 2020.
2. All results are provisional and subject to revision. Due to relatively small number of tests and positive swab tests within the sample, credible intervals are wide and therefore results should be interpreted with caution.
3. These statistics refer to infections reported in the community (i.e. private households). These figures exclude infections reported in hospitals, care homes and/or other communal establishments.
4. Estimates of the total national proportion of the population testing positive for COVID-19 are adjusted to be representative of the population of Northern Ireland that live in private residential households in terms of age, sex and region.
5. Weekly reports are to be published with findings from the COVID-19 Infection survey. It is anticipated that new and further analyses will be added to the weekly reports over time.
6. Further information about quality and methodology associated with the survey can be found on the ONS website.
7. This publication is available online.
8. Additional information is available from:

Information Analysis Directorate
Department of Health
Annex 2, Castle Buildings
Stormont
Belfast BT4 3SQ

Telephone:          028 9052 2340         E-mail: statistics@health-ni.gov.uk

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