Influenza in Ireland – the return of flu

AUTHOR: Priscilla Lynch

Throughout the 2020/2021 influenza season (28 September 2020 – 23 May 2021) there was no evidence of influenza virus circulation in Ireland, according to the Health Protection Surveillance Centre (HPSC).

There were no confirmed influenza notifications reported on the Computerised Infectious Disease Reporting (CIDR) system during the 2020/2021 influenza season compared to 11,142 laboratoryconfirmed influenza notifications reported during the 2019/2020 season, and 7,939 during the 2018/2019 season. This absence occurred despite continued testing for influenza throughout the Covid-19 pandemic and an increase in sentinel GP influenza-like illness (ILI) testing by the National Virus Reference Laboratory (NVRL) during the 2020/2021 season.

This was the first time since influenza surveillance began in Ireland that no influenza circulated during the winter influenza season, and has been attributed to the impact of the Covid-19 pandemic and related restrictions on travel/movement/ mixing, and increased hygiene measures.

Minimal influenza activity was also observed globally during this time. The World Health Organisation (WHO) and the European Centre for Disease Prevention and Control (ECDC) reported influenza at much lower levels than normally expected for the 2020/2021 influenza season, with only sporadic detections of influenza A and B identified. Since the beginning of September 2021, however, there has been an increase in the number of influenza virus detections in Europe, albeit at lower levels than previous years.

Summary of influenza activity in Ireland 2021/2022

Since October 2021 (2021/2022 influenza season to week 17, 2022), a total of 1,947 laboratory-confirmed influenza cases in Ireland have been notified to the HPSC.

Currently influenza viruses are still circulating in Ireland, but are continuing to decrease.

A total of 48 confirmed influenza cases were notified during the week ending April 30 (week 17, 2022), compared to 135 cases in week 14 (ending April 10, 2022). The median age of the 65 notified cases in week 15 was 37 years. Of the 65 cases, 20 (30.8 per cent) were reported as hospital inpatients, with a median age of 33 years.

The overall influenza positivity rate reported from the NVRL was 6.8 per cent for week 16, and 7.7 per cent for week 15, compared to 13.4 per cent during week 13, 2022.

The sentinel GP ILI consultation rate decreased to 9.1/100,000 population during week 16, 2022, compared to 12.5/100,000 population during week 14.

For the 2021/2022 influenza season in Ireland (until end week 16, 2022), a total of 449 (23 per cent) cases out of a total 1,947 flu cases were reported as hospital inpatients, including 13 confirmed influenza cases admitted to critical care units.

To-date this season (end week 17, 2022), nine deaths in notified influenza cases have been reported.

A total of 21 influenza outbreaks have been notified – nine hospital outbreaks, two family outbreaks, seven nursing home outbreaks, one outbreak linked to a social gathering, and two in other healthcare settings.

Influenza A (H3) remains the predominant influenza virus circulating in Ireland during the 2021/2022 season to-date.

Vaccination uptake in older people

Every year the HSE recommends annual influenza vaccination to all individuals aged 65 years and older. Prior to the 2020/2021 season, flu vaccines and administration were free only to all medical/GP visit cardholders in this age group.

In 2020, for the 2020/2021 season there was a change in policy in relation to access to free HSE flu vaccination services due to the Covid-19 pandemic, and anticipated pressures on the healthcare system. Under this policy change, all individuals aged 65 years and older were eligible for free flu vaccines and administration regardless of card status in order to minimise cost as a barrier to vaccination.

The average influenza vaccine uptake nationally in those aged 65 years and older attending GP clinics and pharmacies for vaccination was 70.5 per cent during the period September 2020 – August 2021. This represents a substantial increase from the 2019/2020 season.

The uptake is still below the recommended vaccine coverage for all EU Member States (75 per cent), but slightly above the highest uptake recorded during the 2008/09 season (70.1 per cent).

Variation in flu vaccination coverage was observed between age groups, with the highest uptake (79.5 per cent) in those aged 75 years and older and the lowest uptake in those aged 65-to-69 years (56.6 per cent). Variation in flu vaccination coverage was also observed between HSE areas, ranging from 62.8 per cent in HSE-NW to 75.1 per cent in HSE-SE. 

References

1. Health Protection Surveillance Centre (HPSC). Influenza season 2020/2021 –Influenza vaccine uptake among those 65 years and older. EPI INSIGHT Vol 22 Issue 6. November 2021. Available at www.hpsc.ie

2. HPSC. Surveillance of influenza, respiratory syncytial virus and other respiratory viruses during the 2020/2021 influenza season. EPI INSIGHT Vol 22 Issue 6. November 2021. Available at www.hpsc.ie