Virological and Epidemiological Situation in the Influenza Epidemic Seasons 2016/2017 and 2017/2018 in Poland

The World Health Organization estimates that influenza virus infects 3–5 million people worldwide every year, of whom 290,000 to 650,000 die. In the 2016/2017 epidemic season in Poland, the incidence of influenza was 1,692 per 100,000 population. The influenza A virus, subtype A/H3N2/, was the predominant one in that season. However, in the most recent 2017/2018 epidemic season, the incidence exceeded 1,782 per 100,000 already by August of 2018. In this season, influenza B virus predominated, while the A/H1N1/pdm09 strain was most frequent among the influenza A subtypes. The peak incidence, based on the number of clinical specimens tested, was in weeks 4–5 of 2017 and week 8 of 2018 in the 2016/2017 and 2017/2018 epidemic seasons, respectively. As of the 2017/2018 season, a quadrivalent vaccine, consisting of two antigens of influenza A subtypes and another two of influenza B virus, was available in Poland. Nonetheless, the vaccination rate remained at one of the lowest level in Europe, fluctuating between 3% and 4% of the general Polish population.