{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,31]],"date-time":"2026-01-31T08:35:10Z","timestamp":1769848510305,"version":"3.49.0"},"reference-count":53,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,1,30]],"date-time":"2026-01-30T00:00:00Z","timestamp":1769731200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002383","name":"King Saud University","doi-asserted-by":"publisher","award":["ORF-2026-933"],"award-info":[{"award-number":["ORF-2026-933"]}],"id":[{"id":"10.13039\/501100002383","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Influenza viruses are characterized by their high mutation rates which require continuous molecular surveillance to ensure the annual effectiveness of influenza vaccines. The current study aimed to investigate the molecular evolution and vaccine match of the 2009 pandemic (A(H1N1) pdm09) virus circulating in Riyadh, Saudi Arabia. A total of 380 nasopharyngeal aspirates (NPAs) were collected during the 2020\u20132023 winter seasons from patients with influenza-like illness. Influenza A virus (IAV) detection, typing, and amplification of hemagglutinin (HA) and neuraminidase (NA) genes were achieved using one-step RT-PCR. The full-length HA and NA genes of 14 selected A(H1N1) pdm09 isolates were sequenced and used for sequence and phylogenetic analysis, which also included sequences of seven A(H1N1) pdm09 isolates collected in Riyadh during the 2024\u20132025 season. IAV was detected in 17.11% samples; A\/H3N2 (9.21%) was somewhat more prevalent than A(H1N1) pdm09 (7.89%). Children aged 0\u20134 years had the highest incidence rate of infection. Comparing the HA1 domain of A(H1N1) pdm09 isolates circulating in Riyadh to the current vaccine strains (A\/Wisconsin\/67\/2022 and A\/Victoria\/4897\/2022), a total of 24 amino acid substitutions were identified. O-linked and N-linked glycosylation sites in the HA and NA proteins of the Riyadh isolates coincided with those of the two vaccine strains. The receptor-binding domain (130-loop) of the HA1 domain showed a persistent S137P substitution in all study isolates; this mutation is not present in the current vaccination strain. This finding suggests a potential antigenic mismatch between the current vaccine and the circulating A(H1N1) pdm09 strains in Riyadh, warranting hemagglutination inhibition (HAI) assays to confirm the impact of the S137P substitution on antigenicity and immune evasion. As shown above, ongoing molecular surveillance is essential for guiding the yearly selection of vaccine candidates to increase efficacy.<\/jats:p>","DOI":"10.3390\/ijms27031412","type":"journal-article","created":{"date-parts":[[2026,1,30]],"date-time":"2026-01-30T17:38:34Z","timestamp":1769794714000},"page":"1412","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Molecular Surveillance, Evolution, and Vaccine Strain Match of the HA and NA Genes of 2009 H1N1 Pandemic Virus Circulating in Riyadh, Saudi Arabia"],"prefix":"10.3390","volume":"27","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5337-5381","authenticated-orcid":false,"given":"Reem M.","family":"Aljowaie","sequence":"first","affiliation":[{"name":"Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6970-5207","authenticated-orcid":false,"given":"Ibrahim M.","family":"Aziz","sequence":"additional","affiliation":[{"name":"Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5632-6750","authenticated-orcid":false,"given":"Mohamed A.","family":"Farrag","sequence":"additional","affiliation":[{"name":"Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-7025-6543","authenticated-orcid":false,"given":"Abdulaziz M.","family":"Almuqrin","sequence":"additional","affiliation":[{"name":"Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 12372, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0135-7015","authenticated-orcid":false,"given":"Fahad N.","family":"Almajhdi","sequence":"additional","affiliation":[{"name":"Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,30]]},"reference":[{"key":"ref_1","first-page":"15","article-title":"A review on avian influenza and its economic and public health impact","volume":"4","author":"Gashaw","year":"2020","journal-title":"Int. J. Vet. Sci. Technol."},{"key":"ref_2","first-page":"11","article-title":"Review on classification and nomenclature of viruses","volume":"11","author":"Bimrew","year":"2023","journal-title":"Int. J. Appl. Agric. 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