Epidemic Influenza Seasons from 2008 to 2018 in Poland: A Focused Review of Virological Characteristics

The objective of this review was to elaborate on changes in the virological characteristics of influenza seasons in Poland in the past decade. The elaboration was based on the international influenza surveillance system consisting of Sentinel and non-Sentinel programs, recently adopted by Poland, in which professionals engaged in health care had reported tens of thousands of cases of acute upper airway infections. The reporting was followed by the provision of biological specimens collected from patients with suspected influenza and influenza-like infection, in which the causative contagion was then verified with molecular methods. The peak incidence of influenza infections has regularly been in January-March each epidemic season. The number of tested specimens ranged from 2066 to 8367 per season from 2008/2009 to 2017/2018. Type A virus predominated in nine out of the ten seasons and type B virus of the Yamagata lineage in the 2017/2018 season. Concerning the influenza-like infection, respiratory syncytial virus predominated in all the seasons. There was a sharp increase in the proportion of laboratory confirmations of influenza infection from season to season in relation to the number of specimens examined, from 3.2% to 42.4% over the decade. The number of confirmations, enabling a prompt commencement of antiviral treatment, related to the number of specimens collected from patients and on the virological situation in a given season. Yet influenza remains a health scourge, with a dismally low yearly vaccination rate, which recently reaches just about 3.5% of the general population in Poland.