The Department of Health has 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 22 May 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 the sample, credible intervals are wide and therefore results should be interpreted with caution.

  • During the most recent week of the study (16 May – 22 May), it is estimated that 2,200 people in Northern Ireland had COVID-19 (95% credible interval: 700 to 4,900). 
  • This equates to 0.12% of the population (95% credible interval: 0.04% to 0.27%) or around 1 in 820 people (95% credible interval 1 in 2,630 to 1 in 370).
  • This is based on statistical modelling of the trend in rates of positive nose and throat swab results. Modelling suggests there are early signs of a possible increase in the percentage of people testing positive in the most recent week in Northern Ireland, however infection rates remain low compared with earlier months in the year.
  • In the latest six-week period, there were 15,667 swab tests taken in total from 10,889 participants. Of these, 15 participants tested positive from 14 different households.
  • In the latest two-week period, of the 4,605 participants in the study, 5 tested positive from 5 households.
  • Due to lower positivity rates, additional checks are being undertaken in relation to incidence estimates and no update has been published this week.

New variant analysis

A new variant of the coronavirus (COVID-19) was identified in the UK in mid-November 2020. The new UK variant (B.1.1.7) 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 new 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 new UK variant in COVID-19.

Other variants, including B.1.525 (first identified in Nigeria), may also have this same pattern of gene positivity. At present these are rare in the UK(external link opens in a new window / tab) so this group will continue to be described as compatible with the UK variant, but this will continue to be reviewed.

In contrast other variants of concern including both B.1.617.2 (first detected in India) and B.1.351 (first detected in South Africa) have an S-gene that is detectable with the current test and will therefore be included in the “not compatible with UK variant” group of COVID-19 where the virus level is high enough to identify this. It is not possible to further differentiate within each group of variants (with the same gene pattern) by swab PCR test alone. For cases compatible with the UK variant, rates have likely increased in Northern Ireland in the most recent week. For cases not compatible with the UK variant and cases where the virus is too low to be identifiable, the trend is uncertain.

It should be noted that there is considerable uncertainty around these estimates due to the small numbers of UK variant compatible positives detected in Northern Ireland and also given that not all cases that are positive on the ORF1ab and N-genes will be the UK variant.

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