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Journal of Medical Microbiology logo Journal of Medical Microbiology

Volume 73, Issue 7

Resurgence of influenza with increased genetic diversity of circulating viruses during the 2022–2023 season No Access

Abstract

After two seasons of absence and low circulation, influenza activity increased significantly in the winter of 2022–2023. This study aims to characterize virological and epidemiological aspects of influenza infection in Bulgaria during the 2022–2023 season and perform a phylogenetic/molecular analysis of the hemagglutinin () and neuraminidase () sequences of representative influenza strains.

Influenza A and B viruses generate new genetic groups/clades each season, replacing previously circulating variants. This results in increased antigenic distances from current vaccine strains. Strengthening existing influenza surveillance is essential to meet the challenges posed by the co-circulation of influenza and SARS-CoV-2.

We tested 2713 clinical samples from patients with acute respiratory illnesses using a multiplex real-time RT-PCR kit (FluSC2) to detect influenza A/B and Severe acute respiratory syndrome coronavirus-2(SARS-CoV-2) simultaneously. Representative Bulgarian influenza strains were sequenced at the WHO Collaborating Centres in London, UK, and Atlanta, USA.

Influenza virus was detected in 694 (25.6 %) patients. Of these, 364 (52.4 %), 213 (30.7 %) and 117 (16.9 %) were positive for influenza A(H1N1)pdm09, A(H3N2) and B/Victoria lineage virus, respectively. genes of the 47 influenza A(H1N1)pdm09 viruses fell into clades 5a.2. and 5a.2a.1 within the 6B.5A.1A.5a.2 group. Twenty-seven A(H3N2) viruses belonging to subclades 2b, 2a.1, 2a.1b and 2a.3a.1 within the 3C.2a1b.2a.2 group were analysed. All 23 sequenced B/Victoria lineage viruses were classified into the V1A.3a.2 group. We identified amino acid substitutions in and compared with the vaccine strains, including several substitutions in the antigenic sites.

The study’s findings showed genetic diversity among the influenza A viruses and, to a lesser extent, among B viruses, circulating in the first season after the lifting of anti-COVID-19 measures.

  • Received:
  • Accepted:
  • Published Online:
Keyword(s): aa substitution , genetic characterization , influenza virus , SARS-CoV-2 and vaccine
Funding
This study was supported by the:
  • European Regional Development Fund through the Operational Program Science and Education for Smart Growth 2014–2020 (Award Grant BG05M2OP001-1.002-0001-C04)
    • Principle Award Recipient: IvaChristova
  • Ministry of Health in Bulgaria (Award National Plan of the Republic of Bulgaria for Influenza Pandemic Preparedness)
    • Principle Award Recipient: NeliKorsun
© 2024 The Authors
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2024-07-29
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Resurgence of influenza with increased genetic diversity of circulating viruses during the 2022–2023 season
J. Med. Microbiol. 73, 001864 (2024); https://doi.org/10.1099/jmm.0.001864
/content/journal/jmm/10.1099/jmm.0.001864
/content/journal/jmm/10.1099/jmm.0.001864
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