The number of 3,864,731 cases and suspected cases of influenza and influenza-like viruses in the 2015/2016 influenza epidemic season in Poland was comparable to that present in the preceding season (NIPH-NIH 2015/2016). However, the number of hospitalizations and deaths due to complications increased dramatically. The number of deaths increased from 11 in 2014/2015 to 140 in 2015/2016 (Table 1).

Despite a comparable number of cases and suspected cases of influenza and influenza-like viruses, the number of confirmed cases increased to 40.2% in 2015/2016 up from 21.2% in 2014/2015 (Bednarska et al. 2016). There also was a difference in the most frequent contagion between the two seasons, with subtype A/H1N1/pdm09 (62.6%) predominating in 2015/2016 as opposed to A/H3N2/ predominating the season before in persons over 14 years of age (Hallmann-Szelińska et al. 2016). The present study demonstrates that subtype A/H1N1/pdm09 predominated in all age groups, except for 15–24 years old persons in whom virus type B was dominant (Fig. 2). In both compared seasons, the highest incidence of influenza was reported in the age-groups of 45–64 and 26–44 years and the lowest one in the 15–24 years old persons (Fig. 1) (Bednarska et al. 2016b). Interestingly, the number of confirmed cases of influenza virus was the highest in the same age-groups of 45–64 and 26–44 years in the past 2013/2014 season (Bednarska et al. 2015). We also found that the activity of RSV and PIV-3 was increased in 2015/2016 compared with that in the season before (NIPH-NIH 2015/2016).