During weeks 11 and 12 2016 (weeks ending March 20 and 27, 2016), influenza activity in Ireland decreased significantly. The sentinel GP influenza-like illness (ILI) consultation rate was 16.4 per 100,000 population in week 11 2016 and 20.2 per 100,000 population in week 12 2016, which is close to the Irish baseline ILI threshold (18/100,000 population), following 10 consecutive weeks above baseline levels. Influenza A(H1)pdm09 was the predominant virus circulating this season, co-circulating with influenza B. Overall, positive detections of influenza A(H1)pdm09 and influenza B have decreased each week for the last six weeks. Localised and sporadic influenza activity continues to be reported in Ireland, with on-going reports of confirmed influenza hospitalised cases and critical care admissions.

For the 2015/2016 season to date, a total of 1,601 confirmed influenza hospitalised cases and 127 critical care cases were notified to HPSC. Forty-six notified influenza cases died and were reported to HPSC for the season to date. The majority of severe influenza cases were associated with influenza A(H1)pdm09. The highest age specific rates for hospitalised cases were in those aged less than five years. The number of severe influenza cases has decreased in recent weeks. Influenza A(H1)pdm09 viruses may cause more severe disease in those aged less than 65 years, than A(H3) viruses. Influenza A(H3) was the predominant influenza virus circulating during the 2014/2015 influenza season, which mainly affected the elderly.  

All influenza A(H1)pdm09 and A(H3) viruses characterised in Ireland this season belong to genetic groups that are antigenically similar to the strains recommended for inclusion in the 2015/2016 trivalent influenza vaccines. Influenza B viruses characterised this season in Ireland belong to the B/Victoria lineage; these viruses are not present in the 2015/2016 trivalent vaccine used in Ireland. Trivalent vaccines are the most widely used influenza vaccines in Europe.

In the European Region, influenza A(H1)pdm09 viruses have predominated this season in most countries, although in recent weeks there has been a shift towards influenza B circulation. Influenza activity has peaked in most countries for the 2015/2016 season.

The latest information on influenza surveillance is available on the HPSC website.