{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T11:32:04Z","timestamp":1788867124094,"version":"build-2803163510"},"reference-count":38,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2025,11,30]],"date-time":"2025-11-30T00:00:00Z","timestamp":1764460800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vaccines"],"abstract":"<jats:p>Background: The epidemiology of influenza was disrupted during the COVID-19 pandemic. Following the relaxation of non-pharmaceutical interventions, influenza viruses have re-emerged and caused epidemics with shifts in age distribution and seasonality. This study aimed to characterise the post-pandemic epidemiology of influenza infections among children in Xi\u2019an, China. Methods: A retrospective analysis of laboratory-confirmed paediatric influenza cases spanning three periods [pre-pandemic (1 January 2010\u201322 January 2020), intra-pandemic (23 January 2020\u20138 January 2023), and post-pandemic (9 January 2023\u201331 August 2025)] was conducted. Age-specific incidences were determined by subtypes (lineage) and compared across periods. Seasonal parameters were estimated using a generalised linear model with harmonic terms. Associations between influenza infection and risk of co-detection with other respiratory pathogens were assessed using logistic regression models. Results: Influenza peak activity in the post-pandemic period was 10-fold higher than in the intra-pandemic period. The mean age of infected children increased by 1.4 years (95% CI: 1.2\u20131.7), shifting towards school-aged children (6\u201317 years). The seasonal pattern re-established with an earlier peak (13.9 weeks earlier than the pre-pandemic period, 95% CI: 10.4\u201315.2) and increased amplitude (10-fold and 4-fold higher than the intra- and pre-pandemic periods, respectively). It was observed that A(H1N1)pdm09 positivity was elevated in preschool and school-aged children, whereas B\/Victoria infections showed renewed susceptibility among infants [0\u20135 months vs. 6\u201335 months vs. 3\u20135 years vs. 6\u201317 years: 11.0% (95% CI: 5.1\u201319.8) vs. 2.8% (1.9\u20134.0) vs. 4.0% (3.2\u20135.0) vs. 5.2% (4.5\u20136.0); p = 0.00014]. Influenza infection was associated with higher risk of bacterial co-detection with Streptococcus pneumoniae (aOR = 1.52, 95% CI: 1.22\u20131.91) and Haemophilus influenzae (aOR = 1.46, 95% CI: 1.19\u20131.80), but lower risk of co-detection with SARS-CoV-2 (aOR = 0.52, 95% CI: 0.27\u20130.99), RSV (aOR = 0.29, 95% CI: 0.11\u20130.79), and parainfluenza viruses (aOR = 0.16, 95% CI: 0.04\u20130.65). Conclusions: The post-pandemic landscape of paediatric influenza in Xi\u2019an has undergone substantial reconfiguration, characterised by intensified activity, altered seasonality, and a marked shift in age distribution. The increased bacterial co-detection points out the potential for more severe respiratory co-infections. These findings highlight the importance of optimising vaccination timing and prompting school-aged-children-targeted immunisation programmes in the post-pandemic era.<\/jats:p>","DOI":"10.3390\/vaccines13121214","type":"journal-article","created":{"date-parts":[[2025,12,1]],"date-time":"2025-12-01T08:13:49Z","timestamp":1764576829000},"page":"1214","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Changing Epidemiology of Influenza Infections Among Children in the Post-Pandemic Period: A Case Study in Xi\u2019an, China"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1695-8382","authenticated-orcid":false,"given":"Zeyao","family":"Zhao","sequence":"first","affiliation":[{"name":"Key Laboratory of Public Health Safety, Ministry of Education, School of Public Health, Fudan University, Shanghai 200032, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0008-5329-0183","authenticated-orcid":false,"given":"Ning","family":"Lan","sequence":"additional","affiliation":[{"name":"Department of Infectious Disease Control and Prevention, Xi\u2019an Center for Disease Control and Prevention, Xi\u2019an 710061, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yang","family":"Chen","sequence":"additional","affiliation":[{"name":"The Second Ward of Infectious Diseases, Shangluo Central Hospital, Shangluo 726000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5028-2227","authenticated-orcid":false,"given":"Juan","family":"Yang","sequence":"additional","affiliation":[{"name":"Key Laboratory of Public Health Safety, Ministry of Education, School of Public Health, Fudan University, Shanghai 200032, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jing","family":"Bai","sequence":"additional","affiliation":[{"name":"Shangluo City Center for Disease Control and Prevention, Shangluo 726000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7673-8461","authenticated-orcid":false,"given":"Jifeng","family":"Liu","sequence":"additional","affiliation":[{"name":"Department of Infectious Disease Control and Prevention, Xi\u2019an Center for Disease Control and Prevention, Xi\u2019an 710061, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,11,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.jinf.2020.11.039","article-title":"Impact of non-pharmaceutical interventions targeted at COVID-19 pandemic on influenza burden\u2014A systematic review","volume":"82","author":"Fricke","year":"2021","journal-title":"J. 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