key: cord-0797156-nimxnf6s authors: Bednarska, K.; Hallmann-Szelińska, E.; Kondratiuk, K.; Brydak, L. B. title: Antigenic Drift of A/H3N2/Virus and Circulation of Influenza-Like Viruses During the 2014/2015 Influenza Season in Poland date: 2016-03-09 journal: Respiratory Contagion DOI: 10.1007/5584_2016_216 sha: c125b066248604b02d9c99e26136da61c4ef1821 doc_id: 797156 cord_uid: nimxnf6s Morbidity rates of influenza could be greatly reduced due to vaccination. However, the virus is able to evolve through genetic mutations, which is why vaccines with updated composition are necessary every season. Their effectiveness depends on whether there is a good antigenic match between circulating viruses and vaccine strains. In Poland, the 2014/2015 influenza epidemic started in week 5 (January/February) of 2015 and continued until week 17 (April) of 2015. The influenza activity was moderate with the highest incidence of influence-like illness at week 10/2015 (March). During that season, antigenic drift of influenza virus A/H3N2/ occurred causing higher rates of A/H3N2/ infections. Among the 2416 tested specimens, 22.6 % of influenza cases were positive for A/H3N2/, while A/H1N1/pdm09 constituted 14.6 % cases. Influenza A viruses were detected in co-circulation with influenza B viruses; the latter amounted to 34.1 % of all influenza detections. Other detected causes of influenza-like illness consisted of respiratory syncytial virus (RSV), being predominant, and, sporadically, human coronavirus, parainfluenza 1–3, rhinovirus, and adenovirus. Despite low vaccine effectiveness of solely one component, A/H3N2/, the vaccine could mitigate or shorten the length of influenza infection and reduce the number of severe outcomes and mortality. Thus, vaccination against influenza remains the most effective way to prevent illness and possibly fatal outcomes. Influenza reappears every season and is caused by circulating influenza type A and type B viruses. These viruses evolve through genetic mutations and resulting antigenic changes, what allows them to evade host immunity. Influenza vaccines have to be updated periodically in order to be effective in the following season. Hence, the constant need for seasonal vaccination. As it takes approximately 6 months to produce influenza vaccines, recommendations need to be done in advance. The World Health Organization (WHO) convenes annual meetings in February and September each year to establish the composition of influenza vaccine for the forthcoming season in the northern and southern hemispheres, respectively (Chambers et al. 2015; WHO 2014a; Webster et al. 2013 The 2014/2015 influenza epidemic season in Poland started in week 5 (January/ February) of 2015 and continued until week 17 (April) of 2015. The influenza activity was moderate with the highest incidence of influenza-like illness (ILI) at week 10/2015 (March) (Fig. 1) . During this season, 2416 specimens were tested for influenza and influenza-like viruses, of which 21.2 % (n ¼ 513) were positive for influenza. In detail, there were, 34.1 % (n ¼ 175) influenza type B, 14.6 % (75) influenza A/H1N1/pdm09, 22.6 % (n ¼ 116) influenza A/H3N2/, and 28.7 % (n ¼ 147) non-subtyped influenza type A. There was observed a co-circulation of influenza type A and B viruses, with influenza A being the most prevalent one (Fig. 2) . Infections caused by influenza-like viruses accounted for 11.2 % (n ¼ 270) of tested specimens. Respiratory syncytial virus (RSV) was the other predominant virus, constituting 87.0 % (n ¼ 235) of all ILI cases, followed by sporadic cases of human coronavirus (n ¼ 10, 3.7 %), parainfluenza virus-1 (n ¼ 8, 3.0 %), rhinovirus (n ¼ 6, 2.2 %), adenovirus (n ¼ 5, 1.9 %), and parainfluenza viruses 2 and 3 (n ¼ 3, 1.1 % each (Fig. 3) ). The highest percentage of influenza and ILI confirmed cases was noted in the 0-4 years -group (46.4 %) , followed by the 45-64 years (12.3 %) and 26-44 years age-groups (11.6 %). The lowest morbidity was observed in the 15-25 years (4.9 %) and 10-14 years age-groups (5.4 %) (Fig. 4) . The verification of specimen testing by VSES demonstrated a complete agreement with the results obtained at the National Influenza Center (Table 1) . In the epidemic seasons 2013/2014 and 2014/ 2015 in Poland, the number of specimens received from primary care physicians was similar, although the percentage of influenza and influenza-like infection confirmations was 10 % higher in the latter season. The 2014/2015 morbidity in children aged 0-4 years was twice as much as it had been in the former epidemic season. The vast majority of infections in this group of children was induced by influenza-like viruses (67.2 %). In both seasons, in the case of influenza-like viruses, the predominant virus was RSV. Infections caused by other respiratory viruses occurred sporadically. Influenza cases were caused mainly by influenza type A (83.2 %). The proportion of influenza B was significantly higher in the 2014/2015 season than that in the previous season where it amounted to 1.2 % of all influenza confirmations (Bednarska et al. 2015) . While comparing data from Poland and Europe, it is apparent that the proportion of circulating viruses of influenza type A and B remains similar. In Europe and the whole world alike, the dominant strain was A/H3N2/, but it co-circulated with influenza A/H1N1/pdm09. The predominance of the A/H3N2/ strain also was noted in Poland, even taking into account the fact that not all the specimens tested within the SENTINEL and non-SENTINEL influenza surveillance were subtyped (Broberg et al. 2015; ECDC/WHO 2015; WHO 2015; Rolfes et al. 2014 ). In the 2014/2015 season, antigenic drift of the subtype A/H3N2/ decreased the effectiveness of vaccine against influenza. Yet vaccination remains the most effective and the cheapest method of influenza prevention (Broberg et al. 2015) . Since 1968, the Advisory Committee on Immunization Practices (ACIP) recommends trivalent vaccines against influenza. They contain two subtypes of influenza virus A and one lineage of influenza virus type B. It should be emphasized that people, particularly those who receive vaccination every season, substantially enhance their immunological memory. Evaluation of the activity of influenza and influenza-like viruses in the epidemic season on behalf of the WHO European Region and the European Influenza Surveillance Network (2015) Start of the 2014/15 influenza season in Europe: drifted influenza A (H3N2) viruses circulate as dominant subtype Identification of hemagglutinin residues responsible for H3N2 antigenic drift during the 2014-2015 influenza season From European Centre for Disease Prevention and Control. Circulation of drifted influenza A (H3N2) viruses in the EU/EEA From European Centre for Disease Prevention and Control (ECDC)/World Health Organization Regional Office for Europe (WHO/Europe) Report prepared for the WHO annual consultation on the composition of influenza vaccine for the Northern Hemisphere Report prepared for the WHO annual consultation on the composition of influenza vaccine for the Northern Hemisphere Update: influenza activity -United States Textbook of influenza Recommended composition of influenza virus vaccines for use in the 2014-2015 northern hemisphere influenza season Available from http:// gamapserver.who.int/gareports/Default.aspx? Acknowledgements This work was funded in parts by research projects 2011/01/B/NZ7/06188 and NIPH-NIH's subject 5/EM.1. The authors would like to acknowledge physicians and employees of VSES participating in SEN-TINEL program for their input into the influenza surveillance in Poland. The authors declare no conflicts of interest in relation to this article.