Coronavirus (Covid-19) Infection Survey, Northern Ireland: Weekly Report

Date published: 10 March 2023

The Department of Health today published the next in the series of weekly results from its COVID-19 Infection Survey (CIS).

doh latest statistics

The findings set out in this report relate to modelled positivity estimates for NI for the week up to the 28 February 2023. 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

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.

Variant analysis

The cycle threshold (Ct) value reflects the quantity of virus (also known as viral load) found in a swab test. A lower Ct value indicates a higher viral load. The latest Ct values of coronavirus (COVID-19) positive tests, as well as analysis of the genetic lineages of COVID-19 seen in the samples that are sequenced, are provided in the Coronavirus (COVID-19) Infection Survey: technical dataset.

Since mid-January 2023, the Omicron variant BA.2.75 and its sub-lineages have comprised the largest proportion of all sequenced infections. In the week ending 26 February 2023, of all sequenced infections:

  • BA.2.75 and its sub-lineages (including XBB and CH.1.1 and their respective sub-lineages) comprised 85.8%
  • the sub-lineage CH.1.1 and its sub-lineages comprised 19.7%
  • the sub-lineage XBB.1.5 and its sub-lineages comprised 50.4%, and the sub-lineage XBB.1.9 and its sub-lineages comprised 10.6%
  • BQ.1 (a sub-lineage of Omicron BA.5) and its sub-lineages comprised 11.7%

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 the Coronavirus (COVID-19) Infection Survey methods 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
    Belfast BT4 3SQ
    Telephone:          028 9052 2340         E-mail:

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