Influenza viruses obey no rules: Exceptional Strain variety around the northern hemisphere in the winter of 2018-19

Michal Mandelboim ^1,2 Rakefet Pando ^1,3 Ital Nemet ¹ Shahar Stern ¹ Aharona Glatman-Freedman ^2,3 Hanna Sefty ³ Neta Zukerman ¹ Yaron Drori ¹ Nehemia Friedman ¹ Rodney Daniels ⁴ John Mccaule ⁴ Lital Keinan-Boker ^3,5 Ella Mendelson ^1,2

¹Central Virology Laboratory, Ministry of Health, Chaim Sheba Medical Center, Israel
²Department of Epidemiology and Preventive Medicine,Tel-Aviv University, School of Public Health, Sackler Faculty of Medicine, Israel
³The Israel Center for Disease Control, Israel Ministry of Health, Israel
⁴The Francis, Crick Institute, UK
⁵School of Public Health, University of Haifa, Israel

Background: Influenza is a contagious viral infection causing substantial morbidity and mortality. While vaccination considered the most effective means to prevent influenza morbidity, its effectiveness varies yearly depending on the circulating influenza strains. Seasonal surveillance in Israel in outpatient clinics allows the identification of the circulating influenza strains. Similar surveillance was performed in Europe and USA, (conducted by ECDC (European Center for Disease Control) and CDC (Center for Disease Control)).

Methods: Nasopharyngeal swabs collected from patients with influenza-like illness visiting dozens outpatient clinics in Israel (n=1487) and patients hospitalized in Sheba Medical Center (n=7310) between October-2018 and March-2019 were tested for influenza viruses. Data from this surveillance was compared to the data found in the ECDC, CDC and WHO websites.

Results and Conclusions: In 2018-19 winter, the dominant influenza virus in Israel was A/H3N2, while in Europe and USA, the dominant influenza virus was A/H1N1pdm09 for most of the winter that then changed to A/H3N2. Phylogenetic analysis indicated that the circulating Israeli A/H3N2 belonged to clade-3C.3a, while the vaccine strain, A/Singapore/INFIMH-16-0019/2016-(H3N2)-like-virus, belonged to clade-3C.2a1. Surprisingly, the European and USA A/H3N2 viruses mostly belonged to clade-3C.2a1 at the beginning of the winter, but shifted to clade 3C.3a in the middle of the winter.

The widespread distribution of different subtypes and clades of influenza A/H3N2 during a single season in highlights the need for the development of a universal influenza vaccine matching all virus subtypes, regardless of their genetic changes.