2.1 Episodes of influenza, RSV and COVID-19

The number of new influenza episodes decreased in week 20, with 18 unique episodes identified. There were 28 episodes reported in week 19. The number of new RSV episodes remained stable in week 20, with three unique episodes identified. There was one episode reported in week 19 (Figure 2.1).

Influenza and RSV episode rates by age groups are shown in (Figure 2.2). The highest influenza episode rate in week 20 was in the 0-4 age group (2.7 per 100,000 population). The highest RSV episode rate was in the 75+ year old age group (2.0 per 100,000 population).

Influenza rates across local government districts (LGD) are shown in (Figure 2.3). Antrim and Newtownabbey had the highest influenza rate in week 20 (3.4 per 100,000 population). The highest RSV rate was in Lisburn and Castlereagh (2.0 per 100,000 population).

The number of new COVID-19 episodes decreased in week 20, with 45 unique episodes identified compared with 52 in week 19 (Figure 2.1).

COVID-19 episode rates by age groups are shown in (Figure 2.2). The highest COVID-19 episode rate in week 20 was in the 0-4 age group (9.7 per 100,000 population).

COVID-19 episode rates across LGD are shown in (Figure 2.3). Mid and East Antrim had the highest COVID-19 episode rate in week 20 (5.8 per 100,000 population).

Supplementary tables of key figures are shown at the end of this bulletin.

Figure 2.1: Weekly number of unique episodes of influenza, RSV and COVID-19 by epidemiological week

Figure 2.2: Weekly episode rates of influenza, RSV and COVID-19 per 100,000 population, by age group, by epidemiological week

Figure 2.3: Weekly episode rates of influenza, RSV and COVID-19 per 100,000 population, by local government district, by epidemiological week

2.2 Testing and positivity (%)

In week 20 there were 1,126 total influenza tests, 20 of which were positive (1.8% positivity). This is lower than week 19 (2.5% positivity) (Figure 2.4).

There were 711 total RSV tests, of which four were positive (0.6% positivity). This is similar to week 19 (0.1% positivity) (Figure 2.4).

There were 1,129 COVID-19 tests, 51 of which were positive (4.5% positivity). This is similar to week 19 (4.7% positivity) (Figure 2.4).

Supplementary tables of key figures are shown at the end of this bulletin.

Figure 2.4: Weekly positivity for influenza, RSV and COVID-19, by epidemiological week

2.3 Influenza subtyping

Of the 18 new influenza episodes identified in week 20, two were typed as Flu A (H1), one was typed as Flu A (H3), four were Flu A (not subtyped) and 11 were Flu B (Figure 2.5).

Figure 2.5: Weekly number of unique episodes of influenza, by subtype and epidemiological week

2.4 Sentinel surveillance

Sentinel surveillance plays a role in monitoring and understanding the spread and impact of respiratory viruses like influenza and COVID-19 in the community. It involves a systematic and targeted approach to collect data from a geographical representative subset of GP practices (~18% population representative) to provide information about virus activity across NI.

In week 20, no samples were positive for influenza from five samples submitted for testing to the Regional Virus Laboratory (RVL) (20.0% positivity). Two samples were positive for RSV from five samples submitted for testing(40.0% positivity). No samples were positive for COVID-19 from five samples submitted for testing (Table 1).

Total sentinel cases of influenza, RSV and COVID-19 by age group for the previous year are shown in (Figure 2.6), (Figure 2.7) and (Figure 2.8), and cumulatively for the 2024/25 influenza season in Table 2.

Supplementary tables of key figures are shown at the end of this bulletin.

Figure 2.6: Weekly sentinel influenza cases, by age group, by epidemiological week

Figure 2.7: Weekly sentinel RSV cases, by age group, by epidemiological week

Figure 2.8: Weekly sentinel COVID-19 cases, by age group, by epidemiological week

2.5 Non-sentinel surveillance

Non-sentinel surveillance is the monitoring of respiratory viruses from virology data collected from settings such as hospitals and GPs (excluding the sentinel GPs). This provides information about virus activity across NI.

In week 20, 20 samples were positive for influenza from 1,121 samples submitted for testing to laboratories across NI (1.8% positivity). Three were typed as Flu A (H1), two were Flu A (H3), four were Flu A (not subtyped), and 11 were Flu B. Two samples were positive for RSV from 706 samples submitted for testing (0.3% positivity). 51 samples were positive for COVID-19 from 1,130 samples submitted for testing (4.5% positivity) (Table 3).

Total non-sentinel cases of influenza, RSV and COVID-19 by age group for the previous year are shown in (Figure 2.6), (Figure 2.7) and (Figure 2.11), and cumulatively for the 2024/25 influenza season in Table 4.

Supplementary tables of key figures are shown at the end of this bulletin.

Figure 2.9: Weekly non-sentinel influenza cases, by age group, by epidemiological week

Figure 2.10: Weekly non-sentinel RSV cases, by age group, by epidemiological week

Figure 2.11: Weekly non-sentinel COVID-19 cases, by age group, by epidemiological week

2.6 SARS-CoV-2 variants

In the 8 weeks 24 February 2025 to 20 April 2025, 66 COVID-19 samples were sequenced. Of these, 22 were LP.8.1 (33.3% of all sequenced samples), 6 were JN.1 (9.1% of all sequenced samples), 5 were KP.3 and XEC (both 7.6% of all sequenced samples), 4 were XEC.2 (6.1% of all sequenced samples), 2 were KP and XEC.3 (both 3.0% of all sequenced samples), and 1 was BA.2, XBB.1.5 and XEC.8 (all 1.5% of all sequenced samples). Due to small numbers of samples sequenced, the level of confidence in precision of the estimate is low, and the percentages of each variant may change as further results become available. A more detailed COVID-19 Genomics Bulletin containing a further breakdown of sub-lineages is published weekly.

Parent lineages displayed are subject to change based on lineages under monitoring by the UKHSA horizon scanning team.

Figure 2.12: Total number of sequenced variants of COVID-19 by Pangolin lineage, by epidemiological week

Recombinant refers to any recombinant lineage, starting “X”, that does not fall under the parent lineage of a defined variant.

3.1 Consultation rates for influenza/influenza-like-illness (‘flu/ILI’)

The general practice (GP) flu/ILI consultation rate during week 20 was 2.2 per 100,000 population. This is slightly higher than week 19 (1.8 per 100,000 population). Rates are at baseline activity levels (<10.1 per 100,000 population) (Figure 3.1).

Flu/ILI consultation rates by age groups are shown in Table 5. The highest rate in week 20 was seen in the 75+ age group (2.9 per 100,000 population).

Flu/ILI consultation rates by Health and Social Care Trust (HSCT) are shown in Table 6. The highest rate in week 20 was seen in the Southern Trust (2.3 per 100,000 population).

Since the beginning of the COVID-19 pandemic, the offer of uptake of GP consultations has changed. As a result, consultation rates in the most recent period are unlikely to be directly comparable to pre-pandemic and pandemic years.

Figure 3.1: Northern Ireland GP consultation rates for ‘flu/ILI’ 2021/22 – 2024/25

The baseline MEM threshold for Northern Ireland is <10.1 per 100,000 population for 2024-25. Low activity is 10.1 to <20.5, moderate activity 20.5 to <47.4, high activity 47.4 to <68.5 and very high activity is >68.5 per 100,000 population.

3.2 Consultation rates for acute respiratory infection (ARI)

The GP ARI consultation rate during week 20 was 89.1 per 100,000 population. This is higher than week 19 (71.6 per 100,000 population) (Figure 3.2).

ARI consultation rates by age groups are shown in Table 7. The highest rate in week 20 was seen in the 0-4 age group (367.9 per 100,000 population).

ARI consultation rates by HSCT are shown in Table 8. The highest rates in week 20 were seen in the Western Trust (110.7 per 100,000 population, respectively).

Figure 3.2: Northern Ireland GP consultation rates for ARI 2021/22 – 2024/25

4.1 Influenza, RSV and COVID-19 care homes outbreaks

There was one COVID-19 outbreak reported in a care home setting in week 20. This is similar to week 19. (Figure 4.1).

Figure 4.1: Weekly number of confirmed influenza, RSV and COVID-19 outbreaks, by year and epidemiological week

5.1 Admissions and occupancy

There were 25 new community-acquired emergency hospital admissions during week 20 (Figure 5.1). This is a decrease from week 19 (29 admissions). Of the 25 new admissions, four were Flu A, one was Flu B, one was RSV and 19 were COVID-19.

The 45-64 and 75+ age groups had the majority of community acquired emergency influenza hospital admissions in week 20 (both 40.0%%). There was one RSV hospital admission. The 0-4 age group had the majority of COVID-19 hospital admissions (26.3%).

Community-acquired emergency influenza, RSV and COVID-19 inpatients have remained stable. (Figure 5.2).

Figure 5.1: Weekly number of community-acquired emergency influenza, RSV and COVID-19 hospital admissions, by year and epidemiological week

Figure 5.2: Influenza, RSV and COVID-19 community acquired emergency inpatients, by day

6.1 Deaths related to influenza and/or pneumonia

NISRA death statistics are published weekly. From week ending 31 January 2025 these statistics now include a count of deaths related to influenza and/or pneumonia.

The statistics report on deaths where influenza and/or pneumonia was mentioned anywhere on the death certificate. As a result, the counts will reflect deaths where influenza or pneumonia has contributed to a death but was not necessarily the underlying cause of the death.

The latest data is available from Friday 09 May 2025. In week 19, 60 influenza and/or pneumonia related deaths out of 302 deaths were reported (19.9%). This is a slight decrease from the previous week (68 influenza and/or pneumonia related deaths out of 404 deaths) (Figure 6.1).

Figure 6.1: Weekly deaths and percentage of registered deaths related to influenza and/or pneumonia, to most recent registration week

6.2 Deaths related to COVID-19

NISRA death statistics report on deaths where COVID-19 was mentioned anywhere on the death certificate. As a result, the counts will reflect deaths where COVID-19 has contributed to a death but was not necessarily the underlying cause of the death.

The latest data is available from Friday 09 May 2025. In week 19, there was one COVID-19 related death out of 302 deaths reported (0.3%). This is similar the previous week (two COVID-19 related deaths out of 404 deaths) (Figure 6.2).

Figure 6.2: Weekly deaths and percentage of registered deaths related to COVID-19, to most recent registration week

6.3 Excess Mortality

NISRA use the UK-wide methodology to report on excess deaths as advised by the Office for National Statistics (ONS).

EuroMOMO is a European mortality monitoring activity, aiming to detect and measure excess deaths related to seasonal influenza, pandemics and other public health threats. Reports on excess deaths across Europe and the United Kingdom are published weekly.

8.1 Presentation of data

Unless otherwise stated, data are presented using epidemiological weeks (a standardised method of counting weeks [Monday-Sunday] to allow for the comparison of data year after year). This is dependent on the data available. The data included in this report are the most up to date data available at the time of the report; however, this is subject to change as the data are subject to ongoing quality assurance.

8.2 Virology surveillance

All virology data provided here are preliminary. Virology data for prior weeks, as included in this or future bulletins, are subject to updates based on laboratory returns received after the last report was produced. The current bulletin offers the most current information available.

Rates per 100,000 population are calculated using the NISRA 2021 Mid-Year Population Estimates.

8.3 SARS-CoV-2 genomics

A subset of SARS-CoV-2 positive PCR samples are sent to sequencing laboratories in Belfast Health and Social Care Trust and Queen’s University Belfast for sequencing. On 29th November the lineage assignment algorithm was switched from PangoLEARN to UShER for lineage counts. PangoLEARN uses a machine learning algorithm, whereas UShER uses phylogenetic placement and produces fewer unassigned lineages. This switch has been applied retrospectively, therefore total counts for all lineages have been affected. A more detailed COVID-19 Genomics Bulletin containing a further breakdown of sub-lineages is published weekly.

8.4 Primary care surveillance

Consultation rates for influenza/influenza-like-illness (‘flu/ILI’) and acute respiratory infection (ARI)

GP in-hours consultation data with ~95% coverage of the NI population is auto-extracted weekly from GPIP. This data includes weekly aggregate consultations for ‘flu/ILI’ and ARI, and includes weekly registered patients. The data is available for different Health and Social Care Trusts, and by age and sex.

8.5 Community surveillance

Care home outbreaks

PHA conducts surveillance of outbreaks across multiple settings, including care homes (nursing homes and residential homes) in NI that are registered with the Regulation and Quality Improvement Agency. All care homes have a requirement to notify the PHA Health Protection duty room of suspected outbreaks of any infectious disease. A confirmed outbreak of influenza or RSV can be defined as where there are two or more confirmed cases with onset within a 14 day period, where transmission within the Care Home facility is considered the likely cause.

8.6 Secondary care surveillance

Admissions and occupancy

It is not currently possible for this report to distinguish emergency from other types of admission for each Trusts hospital data following the introduction of a new electronic healthcare record. This was introduced in the SEHSCT on 06/11/2023; BHSCT on 06/06/2024, NHSCT on 07/11/2024, and WHSCT and SHSCT on 28/04/2025. For this report, all community-acquired admissions are included from the respective dates above for each Trust, which will include non-emergency admissions (which are a small minority of the total admissions reported). Only admissions where the method of admission was ‘Emergency’ are counted before these dates for each Trust. Work is ongoing to adapt systems to new data sources and re-instate differentiation of emergency admissions. Ongoing developmental and quality assurance work may result in adjustments to figures.

Influenza and RSV

Community-acquired influenza and RSV emergency admissions to acute hospitals are estimated by combining data from PAS and virological reports in NIHAP. Admissions are counted where there was a positive test up to seven days before admission or up to one day after admission, and the method of admission was ‘Emergency’. The number of inpatients is counted at midnight. Admissions and occupancy refer to the first admission per infection episode.

COVID-19

Community-acquired COVID-19 emergency admissions are estimated by combining data from the NI COVID-19 Combined Testing Register and hospital admission information. Admissions are counted where there was a positive PCR or lateral flow test up to 14 days before admission or up to one day after admission. The number of inpatients is counted at midnight. Admissions and occupancy refer to the first admission per infection episode, including transfers between hospitals. The method used in this report is different to that previously reported by the Department of Health’s COVID-19 dashboard, which used administrative coding to identify COVID-19 admissions.

8.7 Mortality surveillance

NISRA death statistics are published weekly, and include weekly counts of deaths related to influenza and/or pneumonia (new from 31 January 2025), and deaths related to COVID-19. This enables comparisons with weekly information published by the Office for National Statistics (ONS) covering England and Wales.

The statistics report on deaths where influenza and/or pneumonia, or COVID-19, was mentioned anywhere on the death certificate. As a result, the counts will reflect deaths where these diseases have contributed to a death but was not necessarily the underlying cause of the death.

9.1 Unique episodes of influenza, RSV and COVID-19, by epidemiological week, over a six week period

9.2 Influenza, RSV and COVID-19 episode rates per 100,000 population, by age group, over a six week period

9.3 Influenza, RSV and COVID-19 episode rates per 100,000 population, by local government district, over a six week period

9.4 Total tests and positivity for influenza, RSV and COVID-19, by epidemiological week, over a six week period

9.5 Total sentinel tests and positivity for influenza, RSV and COVID-19, by epidemiological week, over a six week period

9.6 Total non-sentinel tests and positivity for influenza, RSV and COVID-19, by epidemiological week, over a six week period

9.7 Number of sequenced samples for variants in Northern Ireland

This table only shows counts for lineages with 10 or more sequenced samples from epidemiological year-week 2024 - 20 onwards. Lineage counts include provisional and confirmed sequencing samples. Lineage calls are subject to change following analysis of genomic sequence results, which may result in fluctuations in lineage counts.