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The objectives of this study were to analyze the pattern of influenza virus circulation with respect to that of severe acute respiratory syndrome coronavirus 2 (SARS\u2010CoV\u20102) in Bulgaria during the 2021\u20132022 season and to perform a phylogenetic\/molecular analysis of the hemagglutinin (<jats:italic>HA<\/jats:italic>) and neuraminidase (<jats:italic>NA<\/jats:italic>) sequences of representative influenza strains. Influenza infection was confirmed using real\u2010time reverse transcription polymerase chain reaction in 93 (4.2%) of the 2193 patients with acute respiratory illness tested wherein all detected viruses were subtyped as A(H3N2). SARS\u2010CoV\u20102 was identified in 377 (24.3%) of the 1552 patients tested. Significant differences in the incidence of influenza viruses and SARS\u2010CoV\u20102 were found between individual age groups, outpatients\/inpatients, and in the seasonal distribution of cases. Two cases of coinfections were identified. In hospitalized patients, the <jats:italic>C<\/jats:italic><jats:sub>t<\/jats:sub> values of influenza viruses at admission were lower in adults aged \u226565 years (indicating higher viral load) than in children aged 0\u201314 years (<jats:italic>p<\/jats:italic>\u2009&lt;\u20090.05). In SARS\u2010CoV\u20102\u2010positive inpatients, this association was not statistically significant. <jats:italic>HA<\/jats:italic> genes of all A(H3N2) viruses analyzed belonged to subclade 3C.2a1b.2a. The sequenced viruses carried 11 substitutions in <jats:italic>HA<\/jats:italic> and 5 in <jats:italic>NA<\/jats:italic>, in comparison to the vaccine virus A\/Cambodia\/e0826360\/2020, including several substitutions in the <jats:italic>HA<\/jats:italic> antigenic sites B and C. This study revealed extensive changes in the typical epidemiology of influenza infection, including a dramatic reduction in the number of cases, diminished genetic diversity of circulating viruses, changes in age, and seasonal distribution of cases.<\/jats:p>","DOI":"10.1002\/jmv.28489","type":"journal-article","created":{"date-parts":[[2023,1,23]],"date-time":"2023-01-23T09:48:40Z","timestamp":1674467320000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":11,"title":["Low prevalence of influenza viruses and predominance of A(H3N2) virus with respect to SARS\u2010CoV\u20102 during the 2021\u20132022 season in Bulgaria"],"prefix":"10.1002","volume":"95","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3188-2283","authenticated-orcid":false,"given":"Neli","family":"Korsun","sequence":"first","affiliation":[{"name":"National Laboratory \u201cInfluenza and ARI\u201d, Department of Virology National Center of Infectious and Parasitic Diseases Sofia Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4543-6831","authenticated-orcid":false,"given":"Ivelina","family":"Trifonova","sequence":"additional","affiliation":[{"name":"National Laboratory \u201cInfluenza and ARI\u201d, Department of Virology National Center of Infectious and Parasitic Diseases Sofia Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7204-6492","authenticated-orcid":false,"given":"Veselin","family":"Dobrinov","sequence":"additional","affiliation":[{"name":"National Laboratory \u201cInfluenza and ARI\u201d, Department of Virology National Center of Infectious and Parasitic Diseases Sofia Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1965-7550","authenticated-orcid":false,"given":"Iveta","family":"Madzharova","sequence":"additional","affiliation":[{"name":"National Laboratory \u201cInfluenza and ARI\u201d, Department of Virology National Center of Infectious and Parasitic Diseases Sofia Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6612-0265","authenticated-orcid":false,"given":"Iliyana","family":"Grigorova","sequence":"additional","affiliation":[{"name":"National Laboratory \u201cInfluenza and ARI\u201d, Department of Virology National Center of Infectious and Parasitic Diseases Sofia Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7878-3995","authenticated-orcid":false,"given":"Iva","family":"Christova","sequence":"additional","affiliation":[{"name":"National Laboratory \u201cInfluenza and ARI\u201d, Department of Virology National Center of Infectious and Parasitic Diseases Sofia Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2023,1,23]]},"reference":[{"key":"e_1_2_11_2_1","doi-asserted-by":"publisher","DOI":"10.1146\/annurev.bi.56.070187.002053"},{"key":"e_1_2_11_3_1","doi-asserted-by":"publisher","DOI":"10.1146\/annurev.iy.08.040190.003513"},{"key":"e_1_2_11_4_1","doi-asserted-by":"publisher","DOI":"10.3390\/ijerph18189525"},{"key":"e_1_2_11_5_1","doi-asserted-by":"publisher","DOI":"10.15585\/mmwr.mm6937a6"},{"key":"e_1_2_11_6_1","doi-asserted-by":"publisher","DOI":"10.1001\/jama.2020.6173"},{"key":"e_1_2_11_7_1","doi-asserted-by":"publisher","DOI":"10.1093\/cid\/ciaa672"},{"key":"e_1_2_11_8_1","doi-asserted-by":"publisher","DOI":"10.3201\/eid2608.201229"},{"key":"e_1_2_11_9_1","doi-asserted-by":"publisher","DOI":"10.2807\/1560-7917.ES.2021.26.11.2100221"},{"key":"e_1_2_11_10_1","unstructured":"ECDC.\u00a0FluNews Europe. 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