This study describes a double-blind randomized placebo-controlled phase I clinical trial in healthy adults of a new potential pandemic H7N9 live attenuated influenza vaccine (LAIV) based on the human influenza virus of Yangtze River Delta hemagglutinin lineage (ClinicalTrials.gov Identifier: NCT03739229). Two doses of H7N9 LAIV or placebo were administered intranasally to 30 and 10 subjects, respectively. The vaccine was well-tolerated and not associated with increased rates of adverse events or with any serious adverse events. Vaccine virus was detected in nasal swabs during the 6 days after vaccination or revaccination. A lower frequency of shedding was observed after the second vaccination. Twenty-five clinical viral isolates obtained after the first and second doses of vaccine retained the temperature-sensitive and cold-adapted phenotypic characteristics of LAIV. There was no confirmed transmission of the vaccine strain from vaccinees to placebo recipients. After the two H7N9 LAIV doses, an immune response was observed in 96.6% of subjects in at least one of the assays conducted.

Interferon-gamma (IFN-y) is a pleiotropic lymphokine that have multiple effects on the growth and differentiation of various types of cells associated with innate immunity. IFN-y induces differentiation ofmyeloid cells, stimulates the expression of major histocompatibility complex (MHC) class II and class I antigens, it is a potent activator of macrophages which destroy antigenic molecules penetrating the cell. IFN-y is widely used for the treatment of infectious diseases, cancer, autoimmune and allergic diseases. Studies conducted in Research Institute ofInfluenza indicate that drugs IFN-y can be successfully usedfor prevention of influenza and acute respiratory infection (ARI) during the rise of incidence, as well as for the treatment - the first few days/ hours of the onset. The concomitant use of drugs as IFN-a and IFN-y on influenza and ARI can greatly improve the prophylactic and therapeutic efficacy.

Pregnant women are at high risk for the adverse course of respiratory diseases, among which the influenza is the one of the leading infections, of ten finishing tragically for most pregnant and her offspring. Due to the disproportionately high morbidity, mortality and adverse outcomes of pregnancy after influenza virus infection, pregnant females are classified as a priority group for vaccination. Immunization with inactivated influenza vaccine is one of the most important strategy to prevent both of influenza infection, its severe complications, and mitigating of the effects of the epidemic of influenza. There was accumulated sufficient evidence demonstrating that the vaccine promotes the diminution of clinical manifestations of influenza infection in pregnant women, as well, has a positive effect on the health of the newborns due to the active transport of maternal antibodies. In the review there are presented data on the safety, high immunogenicity and clinical efficacy of vaccination against influenza as for pregnant women as well for infants.

Monitoring the effectiveness of influenza vaccines annually enables the development of measures aimed at decreasing influenza incidence, hospitalization, and mortality rates. The epidemiological effectiveness of several Russian domestic influenza vaccines was evaluated in St. Petersburg in the 2018-2021 epidemic seasons. Male and female participants (N = 6912) aged 18-23 were monitored from 2018 to 2021. Sovigripp, Grippol Plus, Ultrix, and Ultrix Quadri inactivated influenza vaccines were used for immunization. In 2018-2019, when the vaccine strains fully matched the circulating influenza viruses, prophylactic vaccination resulted in a 2.7 to 7.1-fold reduction in influenza cases. The protective effectiveness of the vaccines against influenza and acute respiratory infections (ARIs) totalled 52.4%, reaching 73.0% effectiveness against influenza after laboratory confirmation. In the epidemic season 2019-2020, when the circulating viruses and vaccine strains did not fully match, the incidence of influenza and ARIs reduced twice due to vaccination; the total vaccine effectiveness against influenza and ARIs amounted to 50.0%. The Grippol Plus, Ultrix, and Ultrix Quadri vaccines proved to be the most effective, demonstrating a total effectiveness of 70.6%-75.0% and a 65.5%-83.5% effectiveness against influenza A and B. In the 2020-2021 epidemic season, no data on the preventive effectiveness of the influenza vaccines could be obtained due to the outbreak of COVID-19 and the absence of detectable influenza virus shedding in the study participants. The results obtained are consistent with WHO experts’ estimates which indicate that modern influenza vaccines reduce the incidence of influenza in adults by 70-90% if the vaccine strains match the circulating virus strains.