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 Northern Ireland for the week up to the 31 December 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).
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 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 (25 December - 31 December), it is estimated that 72,900 people in Northern Ireland had COVID-19 (95% credible interval: 56,800 to 90,100).
- This equates to 3.97% of the population (95% credible interval: 3.10% to 4.91%) or around 1 in 25 people (95% credible interval 1 in 30 to 1 in 20).
- Modelling suggests the percentage of people testing positive continued to increase in the week ending 31 December in Northern Ireland.
- In the latest six-week period, there were 15,350 swab tests taken in total from 11,707 participants. Of these, 327 participants tested positive from 256 different households.
- In the latest two-week period, of the 3,866 participants in the study, 112 tested positive from 92 households.
- In Northern Ireland, the percentage testing positive increased for those of secondary school age, young adults and those aged under 40, but the trend was uncertain for other ages.
- In the week ending 31 December 2021, 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 (see below for more information on the variant analysis undertaken).
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 (B.1.1.529) of COVID-19 has changes in one of the three genes that coronavirus swab tests detect, known as the S-gene. This means in cases compatible with the Omicron variant, 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 the Omicron variant (B.1.1.529). 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 the Omicron variant.