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