2024年10月至2025年5月季节性流感活动概述

18 September2025 Seasonal influenza is an acute respiratory infection caused by influenza virusesthat circulate globallyand year-round.Influenza diseasecan causeillness ranging frommild to severe, sometimes resulting inhospitalizationor death.While mostindividualsrecoverwithin a weekwithout need for medical care,influenzacan lead to serious complicationincluding death, especially amonghigh-riskgroups such asyoung children, the elderly, pregnant women and thosewith underlyingconditions.1 In temperateregions, seasonal influenzatypically peaksduringthe wintermonths, whereasin tropicalareas,influenza viruses can circulateyear-roundwithseasonality and intensity that variesacrosscountries.To supportsurveillance and response efforts, WHO groupscountries, areas and territories(CATs)based on shared patterns of influenzacirculation.2 TheWHO Global Influenza Surveillance and Response System (GISRS)coordinates global influenzasurveillance and monitors and analyzes the spread and evolution of influenza viruses.Data onrespiratory virus surveillanceisprovided to WHO through participation or collaboration with GISRS.CATsreport their data on respiratory through regional platform of the global platformRespiMart(FluNet and FluID).CATsuse a variety of approaches to monitor respiratoryvirus activity and data inthis report may vary from surveillance reports posted elsewhere.3 From October 2024 through May 2025influenza activity was reported in allinfluenzatransmissionzones. The predominant viruses variedacrosstransmission zones and between countries(seeFig. 1). In thetemperate northern hemisphere, influenza activity generally was elevated between December2024 and March 2025 with a peak in January. Influenza A viruses predominated among the reporteddetections, and influenza A(H1N1)pdm09 viruses predominated among the subtyped viruses during thisperiod of increased activity in most transmission zones (seeFig. 2). In thetemperate southern hemisphere, influenza activity generally remained low.In March 2025,influenza activity began to increase in temperate South America, with influenza A(H1N1)pdm09predominant, and Southern Africa, with A(H3N2) predominant (seeFig. 3). Brief summary of seasonal influenza activity, October 2024-May 2025 In Africa,influenza activityinNorthern Africaincreasedin October2024, peaked inDecember2025anddecreased through May.Influenza A(H3N2) viruses predominatedthroughmost ofthis period ofincreased activity.InWestern Africa,influenzaactivity was highest in October andremained atalowlevelfrom December throughMay.InfluenzaA(H3N2) andBvirusespredominated untilDecemberandfrom February, influenza A(H1N1)pdm09 viruses predominated.InMiddle Africa, influenza activitydecreased fromOctoberandremained lowfrom Februarythrough May.Influenza A(H3N2)virusespredominatedthroughJanuary andinfluenza B viruses predominated from February.InEastern Africa,influenza activityincreasedslightlyfrom Februarywith all seasonal subtypes detectedthroughout theperiod.InSouthern Africa, influenza activity increased slightly inMarchwith influenza A(H3N2)viruses predominant. Figs.4a-e.Influenza virus detections by type and subtype, asreported to FluNet, 1 October 2024through31 May 2025. IntheAmericas,influenza activity inNorth AmericaincreasedinNovember, peaked in February anddecreased through May.Influenza A viruses predominated during this period withroughly equalproportions ofA(H1N1)pdm09 and A(H3N2) viruses among subtyped viruses. InCentral America andtheCaribbean,influenza activity increased from November,remained elevatedfrom Januaryto Aprilandpeaked inApril.Influenza A(H3N2) virusespredominated through January and A(H1N1)pdm09viruses predominated from February through May.InTropical South America, influenza activityincreased inApril andremained elevated through Mayand peaked in May.All seasonal subtypescirculated but influenza A(H1N1)pdm09 predominated fromFebruary.InTemperate South America,influenza activity increased in March withA(H1N1)pdm09predominant. In Asia,influenza activity inWestern Asiawas elevatedfrom October to March andpeakedin January,thendecreasedand remained low from April.Influenza A viruses predominatedthroughMarchwithinfluenza A(H1N1)pdm09 predominantthrough mid-January and A(H3N2) viruses predominantfromFebruary,among the subtyped A viruses.Influenza B viruses were also detectedthroughout the period.InCentral Asia, influenza detections were low withA(H1N1)pdm09predominantthrough mid-January andinfluenza B viruses predominantfor the remainder of the period.InEastern Asia, influenza activity, almost exclusively due to influenza A(H1N1)pdm09 virus detections,increased from November, peaked inJanuary and decreased to a low level by March.InSouthern Asia, influenza activityincreasedinNovember, peaked in January and decreased to a low level by March.Influenza A(H1N1)pdm09predominated for most of this periodwith an increased proportion of influenza A(H3N2) viruses sinceMarch and continued B virus detections th