鎴戠畻杈句汉鍚桙br/>Earlierthisyear,birdflupanicwasinfullswing:TheFrenchfearedfortheirfoiegras,theSwisslockedtheirchickensindoors,andAmericansenlistedprisoninmatesinAlaskatohelpspotinfectedwildbirds. 　　TheH5N1virus-previouslyconfinedtoSoutheastAsia-wasstrikingbirdsinplacesasdiverseasGermany,Egypt,andNigeria,andaflupandemicseemedinevitable. 　　Thentheviruswentquiet.ExceptforasteadystreamofhumancasesinIndonesia,thecurrentfluepicenter,thepastyear'sworriesaboutacatastrophicglobaloutbreaklargelydisappeared. 　　Whathappened? 　　Partoftheexplanationmaybeseasonal.Birdflutendstobemostactiveinthecoldermonths,asthevirussurviveslongeratlowtemperatures. 　　"Manyofusareholdingourbreathtoseewhathappensinthewinter,"saidDr.MalikPeiris,amicrobiologyprofessoratHongKongUniversity."H5N1spreadveryrapidlylastyear,"Peirissaid."Sothequestionis,wasthataone-offincident?" 　　Someexpertssuspectpoultryvaccinationhas,paradoxically,complicateddetection.Vaccinationreducestheamountofviruscirculating,butlowlevelsofthevirusmaystillbecausingoutbreaks-withouttheobvioussignsofdyingbirds. 　　"It'snowhardertospotwhat'shappeningwiththefluinanimalsandhumans,"saidDr.AngusNicoll,influenzadirectorattheEuropeanCentresforDiseaseControlandPrevention. 　　Whilethepandemichasnotmaterialized,expertssayit'stooearlytorelax. 　　"Wehaveavisibleriskinfrontofus,"saidDr.KeijiFukuda,coordinatoroftheWorldHealthOrganization'sglobalinfluenzaprogram.Butalthoughtheviruscouldmutateintoapandemicstrain,Fukudapointsoutthatitmightgotheotherdirectioninstead,becominglessdangerousforhumans. 　　H5N1hasprimarilystalkedAsia.Thisyear,however,itcrossedthecontinentaldivide,infectingpeopleinTurkey,Iraq,Egypt,Djibouti,andAzerbaijan. 　　Butdespitethedeathsof154people,andhundredsofmillionsofbirdsworldwidedyingorbeingslaughtered,thevirusstillhasnotlearnedhowtoinfecthumanseasily. 　　Fluvirusesconstantlyevolve,sothemereappearanceofmutationsisnotenoughtoraisealarm.Thekeyistoidentifywhichmutationsarethemostworrisome. 　　"Wedon'treallyknowhowmanychangesthisvirushasgottomaketoadapttohumans,ifitcanatall,"saidDr.RichardWebby,abirdfluexpertatSt.JudeChildren'sResearchHospitalinTennessee. 　　Themostobvioussignthatapandemicmaybeunderwaywillalmostcertainlycomefromthefield:asuddenspikeincasessuggestinghuman-to-humantransmission.Thelastpandemicstruckin1968-whenbirdflucombinedwithahumanstrainandwentontokill1millionpeopleworldwide. 　　InMay,onSumatraislandinIndonesia,aclusterofeightcaseswasidentified,sixofwhomdied.TheWorldHealthOrganizationimmediatelydispatchedateamtoinvestigate. 　　TheU.N.agencywasconcernedenoughbythereportstoputpharmaceuticalscompanyRocheHoldingAGonstandbyincaseitsglobalantiviralstockpile,promisedtoWHOforanyoperationtoquashanemergingpandemic,neededtoberushedtoIndonesia. 　　Luckily,theSumatraclusterwasconfinedtoasinglefamily.Thoughhuman-to-humantransmissionoccurred-asithasinahandfulofothercases-thevirusdidnotadaptenoughtobecomeeas