The Global Influenza Hospital Surveillance Network was established in 2012 to obtain valid epidemiologic data on hospital admissions with influenza-like illness. Here we describe the epidemiology of admissions with influenza within the Northern Hemisphere sites during the 2013/2014 influenza season, identify risk factors for severe outcomes and complications, and assess the impact of different influenza viruses on clinically relevant outcomes in at-risk populations. Eligible consecutive admissions were screened for inclusion at 19 hospitals in Russia, Turkey, China, and Spain using a prospective, active surveillance approach. Patients that fulfilled a common case definition were enrolled and epidemiological data were collected. Risk factors for hospitalization with laboratory-confirmed influenza were identified by multivariable logistic regression. 5303 of 9507 consecutive admissions were included in the analysis. Of these, 1086 were influenza positive (534 A(H3N2), 362 A(H1N1), 130 B/Yamagata lineage, 3 B/Victoria lineage, 40 untyped A, and 18 untyped B). The risk of hospitalization with influenza (adjusted odds ratio [95% confidence interval]) was elevated for patients with cardiovascular disease (1.63 [1.33–2.02]), asthma (2.25 [1.67–3.03]), immunosuppression (2.25 [1.23–4.11]), renal disease (2.11 [1.48–3.01]), liver disease (1.94 [1.18–3.19], autoimmune disease (2.97 [1.58–5.59]), and pregnancy (3.84 [2.48–5.94]). Patients without comorbidities accounted for 60% of admissions with influenza. The need for intensive care or in-hospital death was not significantly different between patients with or without influenza. Influenza vaccination was associated with a lower risk of confirmed influenza (adjusted odds ratio = 0.61 [0.48–0.77]). Influenza infection was detected among hospital admissions with and without known risk factors. Pregnancy and underlying comorbidity increased the risk of detecting influenza virus in patients hospitalized with influenza-like illness. Our results support influenza vaccination as a measure for reducing the risk of influenza-associated hospital admission.

A dramatic increase of influenza activity in Russia since week 3 of 2016 significantly differs from previous seasons in terms of the incidence of influenza and acute respiratory infection (ARI) and in number of lethal cases. We performed antigenic analysis of 108 and whole‐genome sequencing of 77 influenza A(H1N1)pdm09 viruses from Moscow and Saint Petersburg. Most of the viruses were antigenically related to the vaccine strain. Whole‐genome analysis revealed a composition of specific mutations in the internal genes (D2E and M83I in NEP, E125D in NS1, M105T in NP, Q208K in M1, and N204S in PA‐X) that probably emerged before the beginning of 2015/2016 epidemic season.

H2N2 influenza viruses have not circulated in the human population since 1968, but they are still being regularly detected in the animal reservoir, suggesting their high pandemic potential. To prepare for a possible H2N2 pandemic, a number of H2N2 vaccine candidates have been generated and tested in preclinical and clinical studies. Here we describe the results of a randomized, double-blind placebo-controlled phase 1 clinical trial of an H2N2 live attenuated influenza vaccine (LAIV) candidate prepared from a human influenza virus isolated in 1966. The vaccine candidate was safe and well-tolerated by healthy adults, and did not cause serious adverse events or an increased rate of moderate or severe reactogenicities. The H2N2 vaccine virus was infectious for Humans. It was shed by 78.6% and 74.1% volunteers after the first and second dose, respectively, most probably due to the human origin of the virus. Importantly, no vaccine virus transmission to unvaccinated subjects was detected during the study. We employed multiple immunological tests to ensure the adequate assessment of the H2N2 pandemic LAIV candidate and demonstrated that the majority (92.6%) of the vaccinated subjects responded to the H2N2 LAIV in one or more immunological tests, including 85.2% of subjects with antibody responses and 55.6% volunteers with cell-mediated immune responses. In addition, we observed strong correlation between the H2N2 LAIV virus replication in the upper respiratory tract and the development of antibody responses.

The COVID-19 pandemic had a profound impact on influenza activity worldwide. However, as the pandemic progressed, influenza activity resumed. Here, we describe the influenza epidemic of high intensity of the 2022–2023 season. The epidemic had an early start and peaked in week 51.2022. The extremely high intensity of the epidemic may have been due to a significant decrease in herd immunity. The results of PCR-testing of 220,067 clinical samples revealed that the influenza A(H1N1)pdm09 virus dominated, causing 56.4% of positive cases, while A(H3N2) influenza subtype accounted for only 0.6%, and influenza B of Victoria lineage—for 34.3%. The influenza vaccine was found to be highly effective, with an estimated effectiveness of 92.7% in preventing admission with laboratory-confirmed influenza severe acute respiratory illness (SARI) cases and 54.7% in preventing influenza-like illness/acute respiratory illness (ILI/ARI) cases due to antigenic matching of circulated viruses with influenza vaccine strains for the season. Full genome next-generation sequencing of 1723 influenza A(H1N1)pdm09 viruses showed that all of them fell within clade 6B.1A.5.a2; nine of them possessed H275Y substitution in the NA gene, a genetic marker of oseltamivir resistance. Influenza A(H3N2) viruses belonged to subclade 3C.2a1b.2a.2 with the genetic group 2b being dominant. All 433 influenza B viruses belonged to subclade V1A.3a.2 encoding HA1 substitutions A127T, P144L, and K203R, which could be further divided into two subgroups. None of the influenza A(H3N2) and B viruses sequenced had markers of resistance to NA inhibitors. Thus, despite the continuing circulation of Omicron descendant lineages, influenza activity has resumed in full force, raising concerns about the intensity of fore coming seasonal epidemics.

Influenza circulation was substantially reduced after March 2020 in the European region and globally due to the wide introduction of non-pharmaceutical interventions (NPIs) against COVID-19. The virus, however, has been actively circulating in natural reservoirs. In summer 2021, NPIs were loosened in Russia, and influenza activity resumed shortly thereafter. Here, we summarize the epidemiological and virological data on the influenza epidemic in Russia in 2021–2022 obtained by the two National Influenza Centers. We demonstrate that the commonly used baseline for acute respiratory infection (ARI) is no longer sufficiently sensitive and BL for ILI incidence was more specific for early recognition of the epidemic. We also present the results of PCR detection of influenza, SARS-CoV-2 and other respiratory viruses as well as antigenic and genetic analysis of influenza viruses. Influenza A(H3N2) prevailed this season with influenza B being detected at low levels at the end of the epidemic. The majority of A(H3N2) viruses were antigenically and genetically homogenous and belonged to the clade 3C.2a1b.2a.2 of the vaccine strain A/Darwin/9/2021 for the season 2022–2023. All influenza B viruses belonged to the Victoria lineage and were similar to the influenza B/Austria/1359417/2021 virus. No influenza A(H1N1)pdm09 and influenza B/Yamagata lineage was isolated last season.

Background. The vaccine is the best available instrument to prevent influenza and reduce the risks of major disease complications and mortality. The vaccine effectiveness during the influenza season depends on a number of factors: (1) a person vaccinated (their age and health status); (2) the vaccine formulation; (3) types and subtypes of the circulating viruses; (4) vaccination timeline, as the immune response fades over time. An influenza vaccine can yield different effectiveness in people who have been infected or vaccinated previously and in those who have not been yet exposed to the circulating viruses. At present, trivalent and quadrivalent influenza vaccines are registered and produced in Russia. It allows for vaccination of all social groups, including high-risk populations, and for increasing the number of vaccinated individuals yearly. Russian Federation constantly improves the production of influenza vaccines, introducing new variants of vaccine formulations into national clinical usage. It is thus essential to monitor and analyze the changes in the effectiveness of influenza vaccines every season.Aim of the study. To evaluate of the effectiveness of Russian domestic influenza vaccines during the epidemic season 2019–2020 in St. Petersburg compared to the season 2018–2019.Materials and Methods. 3315 female and male adult participants aged 18 years and older were monitored from October 2019 to March 2020. The group included university students and tutors, researchers, and production and office workers of industrial enterprises. Sovigripp, Grippol Plus, Ultrix, and Ultrix Quadri influenza vaccines were used for immunization.Results and Discussion. In the context of incomplete correspondence between the viruses circulating in Russia and the strains used in the vaccines, the vaccination of the St. Petersburg population during the epidemic season 2019-2020 with Sovigripp, Grippol Plus, Ultrix, and Ultrix Quadri influenza vaccines cumulatively reduced influenza and ARI incidences by half; the total vaccine effectiveness against influenza and ARI amounted to 50.0%. The strongest preventive effect was identified for Grippol Plus, Ultrix, and Ultrix Quadri which demonstrated the total vaccine effectiveness from 70.6% to 75.0%, and their effectiveness against influenza A and B viruses reached from 65.5% to 83.5%.Conclusion. In the context of incomplete correspondence between the viral strains used in the vaccines and the strains circulating in Russia and St. Petersburg during the epidemic season 2019- 2020 and considering the active circulation of non-influenza viruses such as rhinoviruses and adenoviruses, we found a moderate preventive effectiveness of the influenza vaccines during the seasonal epidemic increase in ARI cases. Russian domestic influenza vaccines were shown to have good acceptability, be safe, and non-reactogenic.