Flu yesterday, today and tomorrow. The results of monitoring immunization and morbidity in the epidemic seasons 2019–2020, 2020–2021, 2021–2022, 2022–2023

BACKGROUND: This study presents the epidemiological characteristics of influenza in the last four influenza seasons across the years 2019–2023 The analysis of vaccination and morbidity monitoring data have shown the high effectiveness of influenza vaccine prophylaxis. The influenza vaccines registered in Russia are considered, and their features, composition, and advantages are indicated. Recommendations for their use are provided, including aspects of vaccination of persons belonging to risk groups.

AIM: This study aimed to analyze the epidemiological features of influenza seasons in 2019–2020, 2020–2021, 2021–2022, and 2022–2023, and evaluate the effectiveness of domestic influenza vaccines in mass immunization of the Russian population.

MATERIALS AND METHODS: Information from the official website of the Research Institute of Influenza of the Ministry of Health of the Russian Federation, data from the state report “On the State of Sanitary and Epidemiological Welfare of the Population in the Russian Federation” for 2021 and 2022, materials from conferences and congresses on influenza, and information and analytical certificates from the Ministry of Health of the Russian Federation were evaluated. Monitoring included the rapid collection, analysis, synthesis of information on immunization in the Russian Federation (in different age, social, and professional groups of the population), and analysis of influenza incidence, among others. Preventive effectiveness was determined by the following indicators: morbidity per 100,000 population, efficiency index (K) expressed in conventional units (units), and efficiency coefficient (protection) (E) expressed in %.

RESULTS: The COVID-19 pandemic had significantly affected the quantitative characteristics of seasonal influenza epidemics. In the influenza seasons 2020–2021 and 2021–2022, the predominance of the SARS-CoV-2 virus resulted in the temporary “displacement” of influenza viruses from the human population, and influenza incidence decreased to a historical minimum (0.07 per 100,000 population) in 2020–2021. In the epidemic season 2022–2023, high activity of influenza viruses was noted with the continued high coverage of immunization against influenza in the Russian Federation population (52.8%). The incidence rate of influenza in 2022–2023 was 60.80 per 100,000 people. The incidence among those vaccinated was only 4.23 per 100,000 people, which confirms the effectiveness of vaccination. The etiological structure was dominated by the influenza A(H1N1)pdm09 virus. Of 149,000 cases of registered influenza (with laboratory confirmation, 136,600 cases), 3,276 people (2% of the number of cases) were vaccinated. Most patients had concomitant diseases.

CONCLUSIONS: In the post-pandemic period, against the background of simultaneous circulation of influenza viruses and SARS-CoV-2, an increase in morbidity, caused primarily by influenza A viruses, is expected. Seasonal vaccination is a strategy to ensure the protection of the population from influenza. Annual immunization against influenza with coverage of at least 40% of all social and professional groups of the population remains effective in reducing the severe forms of diseases and mortality. Vaccination helps avoid an increase in morbidity and mass hospitalization and thus significantly reduces the burden on the healthcare system. Special attention should be paid to vaccination of pregnant, people aged >60 years and patients with chronic diseases.