SUMMARY OF INFLUENZA AND OTHER RESPIRATORY VIRUSES DETECTED AND CHARACTERIZED IN RUSSIA DURING 2017-2018 SEASON

The influenza season 2017-2018 started significantly later compared to the five previous seasons. Influenza epidemic lasted for 12 weeks (weeks 6-17), was of moderate intensity and 10,4% of the population of the country was involved with children aged 0-2 and 3-6 years being the most affected groups as usually. The average hospitalization rate of patients with ILI and ARI was 2,6% and was the highest in infants aged 0-2 years (5,4%). The number of influenza-associated deaths was two times higher this season compared to 2016-2017 which can be attributed to the circulation of A(H1N1)pdm09 viruses that still is the major cause of lethal influenza outcomes in the country. A total 72 759 patients were investigated by RT-PCR in 55 collaborating RBLs. Laboratory confirmed influenza (LCI) was detected in 12 149 (20.7%) cases, of which 39.3% were influenza A(H1N1) pdm09 viruses, 29.6% were A(H3N2) and 31.1% influenza B (Yamagata lineage) viruses. The first cases of influenza viruses were detected at the very beginning of the season (weeks 40-45.2017), however a distinct increase in the rate of detection was registered only from the week 2.2018 with the peak on the week 13-14.2018 and subsequent gradual decline up to the end of the season. The certain differences in the etiology of morbidity between Federal Districts were registered. The impact of influenza and other ARI agents in different stage of epidemic was determined. In the pre-epidemic period, the incidence growth was occurred mainly due to ARI agents (about 32,7%), especially due to rhinoviruses (RhV) and RSV (10.2 and 8.0% cases, respectively) while LCI were registered in 3.4% only. During the epidemic, the rate of LCI detection increased up to 29.2% at simultaneous decrease in frequency of parainfluenza, adenovirus, bocavirus, coronavirus and, especially, rhinoviruses, to a lesser extent RSV infection. In the post-epidemic period, the role of influenza A(H1N1) pdm09, A(H3N2) and. viruses decreased up to 6.1; 6.9 and 3.6%, respectively, with increase of rhinoviruses (9.5% of diseases). Genetic analysis of influenza A(H1N1) pdm09 and A(H3N2) viruses circulating in 2017-2018 season showed that all analyzed viruses by the structure of surface genes encoding antigenic determinants, in difference from influenza B viruses, corresponded to the vaccine strains recommended by WHO for the Northern Hemisphere for 2017-2018 epidemic season. However, significant changes in the internal genes of circulating viruses were revealed. The control of the susceptibility of 316 influenza A and B viruses to antiviral drugs showed that the absolute majority of them (99.7%) retained their susceptibility to neuraminidase inhibitors.