{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,2]],"date-time":"2026-10-02T04:00:56Z","timestamp":1790913656425,"version":"4.1.0"},"reference-count":40,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2024,7,11]],"date-time":"2024-07-11T00:00:00Z","timestamp":1720656000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>The unexpected emergence of oseltamivir-resistant A(H1N1) viruses in 2008 was facilitated in part by the establishment of permissive secondary neuraminidase (NA) substitutions that compensated for the fitness loss due to the NA-H275Y resistance substitution. These viruses were replaced in 2009 by oseltamivir-susceptible A(H1N1)pdm09 influenza viruses. Genetic analysis and screening of A(H1N1)pdm09 viruses circulating in Germany between 2009 and 2024 were conducted to identify any potentially synergistic or resistance-associated NA substitutions. Selected viruses were then subjected to further characterization in vitro. In the NA gene of circulating A(H1N1)pdm09 viruses, two secondary substitutions, NA-V241I and NA-N369K, were identified. These substitutions demonstrated a stable lineage in phylogenetic analysis since the 2010\u20132011 influenza season. The data indicate a slight increase in viral NA bearing two additional potentially synergistic substitutions, NA-I223V and NA-S247N, in the 2023\u20132024 season, which both result in a slight reduction in susceptibility to NA inhibitors. The accumulation of secondary synergistic substitutions in the NA of A(H1N1)pdm09 viruses increases the probability of the emergence of antiviral-resistant viruses. Therefore, it is crucial to closely monitor the evolution of circulating influenza viruses and to develop additional antiviral drugs against different target proteins.<\/jats:p>","DOI":"10.3390\/v16071109","type":"journal-article","created":{"date-parts":[[2024,7,11]],"date-time":"2024-07-11T11:30:55Z","timestamp":1720697455000},"page":"1109","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Increase of Synergistic Secondary Antiviral Mutations in the Evolution of A(H1N1)pdm09 Influenza Virus Neuraminidases"],"prefix":"10.3390","volume":"16","author":[{"given":"Susanne C.","family":"Duwe","sequence":"first","affiliation":[{"name":"Unit 17 Influenza and Other Respiratory Viruses, Department 1 Infectious Diseases, Robert Koch-Institute, 13353 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeanette","family":"Milde","sequence":"additional","affiliation":[{"name":"Unit 17 Influenza and Other Respiratory Viruses, Department 1 Infectious Diseases, Robert Koch-Institute, 13353 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alla","family":"Heider","sequence":"additional","affiliation":[{"name":"Unit 17 Influenza and Other Respiratory Viruses, Department 1 Infectious Diseases, Robert Koch-Institute, 13353 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marianne","family":"Wedde","sequence":"additional","affiliation":[{"name":"Unit 17 Influenza and Other Respiratory Viruses, Department 1 Infectious Diseases, Robert Koch-Institute, 13353 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Brunhilde","family":"Schweiger","sequence":"additional","affiliation":[{"name":"Unit 17 Influenza and Other Respiratory Viruses, Department 1 Infectious Diseases, Robert Koch-Institute, 13353 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3432-0438","authenticated-orcid":false,"given":"Ralf","family":"D\u00fcrrwald","sequence":"additional","affiliation":[{"name":"Unit 17 Influenza and Other Respiratory Viruses, Department 1 Infectious Diseases, Robert Koch-Institute, 13353 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2024,7,11]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"4638","DOI":"10.1002\/jmv.26990","article-title":"A brief review of influenza virus infection","volume":"93","author":"Javanian","year":"2021","journal-title":"J. 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