Coronavirus (Covid-19) Infection Survey Northern Ireland – 11 - 17 July 2021

Date published: 23 July 2021

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 Northern Ireland for the week up to the 17 July 2021. 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 residences).

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.

  • During the most recent week of the study (11 July – 17 July), it is estimated that 10,900 people in Northern Ireland had COVID-19 (95% credible interval: 5,700 to 17,900). 
  • This equates to 0.59% of the population (95% credible interval: 0.31% to 0.98%) or around 1 in 170 people (95% credible interval 1 in 320 to 1 in 100).
  • Modelling suggests the percentage of people testing positive increased in the week ending 17 July in Northern Ireland.
  • In the latest six-week period, there were 14,351 swab tests taken in total from 10,525 participants. Of these, 34 participants tested positive from 28 different households.
  • In the latest two-week period, of the 4,381 participants in the study, 16 tested positive from 15 households.

New variant analysis

A new variant of the coronavirus (COVID-19) was identified in the UK in mid-November 2020. The Alpha variant (B.1.1.7, previously known as the UK variant) of COVID-19 has changes in one of the three genes which coronavirus swab tests detect, known as the S-gene. This means in cases compatible with the Alpha variant, the S-gene is no longer detected by the current test. While there are other reasons why a positive swab test may not detect the S-gene, absence of the S-gene has become a reliable indicator of the Alpha variant in COVID-19.

Other variants, including Eta (B.1.525), also have this same pattern of gene positivity as Alpha (B.1.1.7). At present these are rare in the UK so this group will continue to be described as compatible with the Alpha variant, but this will continue to be reviewed.

In contrast other variants of concern including both Delta (B.1.617.2) and Beta (B.1.351) are positive on all three genes, with the pattern ORF1ab+S+N. Almost all ORF1ab+S+N cases in the UK will now be the Delta variant, so this group is labelled “Compatible with the Delta variant”. The main variant analysis can therefore differentiate between these two groups of variants (ORF1ab+N positive or ORF1ab+S+N positive), but cannot differentiate between variants that have the same gene pattern for the three genes that COVID-19 swab tests detect. As Delta has been the main variant in the UK for several weeks it is possible that some Delta variant infections do not test positive on the three genes, particularly if there is a low viral load. These numbers are expected to be small, but it is possible that some Delta cases may be categorised as Alpha compatible.

In the week ending 17 July in Northern Ireland, the percentage of people testing positive whose results are compatible with the Delta variant (B.1.617.2) increased whilst the rates are low for those whose results are compatible with the Alpha variant (B.1.1.7). The trend is uncertain for those where the virus is too low for the variant to be identifiable.

It should be noted that there is considerable uncertainty around these estimates due to the low number of positive results in Northern Ireland. Additionally, there are uncertainties given that not all cases that are positive on the ORF1ab and N-gene will be the Alpha variant, and not all cases that are positive on all three of the ORF1ab, N-gene and S-gene will be the Delta variant.

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.
  1. 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.
  1. 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 institutional settings.
  1. 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.
  1. 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.
  1. Further information about quality and methodology associated with the survey can be found on the ONS website.

  1. This publication is available online
  1. Additional information is available from:

Information Analysis Directorate
Department of Health
Annex 2, Castle Buildings
Belfast BT4 3SQ
Telephone: 028 9052 2340     

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