Influenza - a problem still existing during the COVID-19 pandemic.

Address for correspondence: Lidia B. Brydak, National Institute of Public Health – National Research Institute, 24 Chocimska St., 00-791 Warsaw, Poland, e-mail: lbrydak@pzh.gov.pl Submitted: 29.04.2023; Accepted: 12.05.2023 Influenza has always been and will be in years to come a global and public health problem. Therefore the improvement and expansion of the Global Influenza Surveillance and Response System (GISRS) should be a priority for the healthcare community [1]. In 1947, at the 4th International Congress of Microbiologists in Copenhagen, the World Health Organization (WHO) foundations were laid for the future GISRS (which was finally created in 1952 and in 2022 celebrated its 70th anniversary) with the establishment of the first seven WHO Collaborating Centers for Reference and Research on Influenza in their current form. Since 1957 Poland has been participating in this system for monitoring influenza, as one of 149 National Influenza Centers worldwide. Poland was responsible for the introduction of the SENTINEL surveillance methods during its leadership of GISRS in the 2004/2005 epidemic season [2]. Virological data obtained by the Collaborating Centers for Reference and Research on Influenza are reported to the WHO and the European Union Agency: European Centre for Disease Prevention and Control (ECDC) [3]. As an example of such data, the information provided to the WHO by Poland concerning epidemic seasons from 2015/2016 to 2022/2023, including the time when the COVID-19 pandemic took place, is presented in Table I. On March 11, 2020, the WHO announced the COVID-19 pandemic. As shown in Table I, the values of all the indicators used for influenza monitoring were definitely lower at the time of the pandemic. This phenomenon is attributed to the fact that a significant part of the population worked remotely, including schools and universities, and mandates to wear masks were introduced to avoid the transmission of respiratory infections. The number of deaths resulting from post-influenza complications reported in Poland is underestimated – which is true not only in the case of data presented in Table I, as some deaths are attributed to the wrong disease entity. In the 2021/2022 epidemic season, i.e. from October 1, 2021 to September 30, 2022, a total of 2,317 samples