EPIDEMIOLOGICAL CHARACTERISTICS OF ACUTE RESPIRATORY INFECTIONS AND INFLUENZA IN THE SEASON 2023–2024
Authors:   SI"L.V. Gromashevsky Institute of Epidemiology and Infectious Diseases of National Academy of Medical Science of Ukraine", Kyiv, Zadorozhna V.I 
Published: February 2025

Background. infections (ARI), especially in the first years of the pandemic. Influenza B virus of the B/Yamagata lineage has stopped circulating. The ARI and influenza season of 2023–2024 was the first after the end of the COVID-19 COVID-19 has significantly affected the intensity of the epidemic process of acute respiratory
pandemic.
The aim of the study was to investigate the epidemiological features of influenza and other ARI in the 2023–2024
season in the world, its individual regions and Ukraine.
Materials and methods. The work uses materials from various sources of medical statistics (official statistics of
the Ministry of Health of Ukraine, the State Institution “Center for Public Health of the Ministry of Health of Ukraine”,
the State Institution “Center for Medical Statistics of the Ministry of Health of Ukraine”) The methods used in the work
are: bibliosemantic, epidemiological, mathematical statistics.
Results and discussion. In the world during this period, viruses of clades 5a.2a (subclade C.1) and 5a.2a.1 (C.1.1.1) dominated
among A(H1N1) viruses, 2a.3a.1 (J.2) among A(H3N2), and V1A.3a.2 among B(Victoria). In the United States, with A(H1N1) playing
the leading role, A(H3N2) and B viruses were detected about 2 times less frequently. In the European region, compared to the
previous season, the proportion of A(H1N1) increased from 61% to 74%, and A(H3N2) decreased (from 39% to 26%). The vaccinelike viruses of the corresponding season included 23% of the studied A(H1N1) strains, 6% of A(H3N2), 9% of B/Victoria. During
this season, 4.8 million people fell ill with ARI (including influenza and COVID-19) in Ukraine (13 391.1 per 100 thousand people),
which is 22.7% more than last season. Children prevailed among the cases (55.8%), which is typical for ARI and indicates that
the COVID-19 pandemic has lost its activity. The incidence among children was 5.9 times higher than among adults. The
dynamics of ARI was wave-like. The incidence was significantly lower in the areas where military operations took place. For
influenza, there was a slight increase (November — early December 2023) and an intense increase (December–February
2024). Children prevailed among the cases (55.8%), which is typical for ARI and is an indication that the COVID-19 pandemic
has lost its activity. The incidence among children was 5.9 times higher than among adults. The dynamics of ARI was wavelike. The incidence was significantly lower in the areas where military operations took place. For influenza, there was a slight
increase (November — early December 2023). 17 636 cases of influenza were registered (0.36% of all SARS, 3.9 times lower than
COVID-19), of which 55.88% were among children. The mortality rate was 0.41% (72 cases), although this figure is actually
much lower, given the underdiagnosis of influenza. Influenza viruses accounted for 49.8% of respiratory viruses. They also
circulated during the off-season. Compared to the previous season, there was a more than 2-fold decrease in the share
of SARS-CoV-2 and an increase in other viruses (adeno- — 4.2 times, parainfluenza viruses — 3.2 times, RSV — from 19.0% to
25.6%). The unexpected rise in the incidence of COVID-19 in the inter-epidemic period of 2024 requires investigation.