2017
Early risk assessment:What to expect of the 2017/18 influenza season in Norway
REPORT
Earlyriskassessment:
Whattoexpectofthe2017/18influenzaseasoninNorway
DepartmentofInfluenza
What to expect of the 2017/18 influenza season in Norway • Norwegian Institute of Public Health
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PublishedbyNorwegianInstituteofPublicHealthDivisionofInfectionControlandEnvironmentalHealthDepartmentofInfluenzaDecember2017
Title:Earlyriskassessment:Whattoexpectofthe2017/18influenzaseasoninNorway
Author(s):DepartmentofInfluenza
Thereportcanbedownloadedaspdfatwww.fhi.no/en/publ/
Graphicdesigntemplate:PerKristianSvendsenandGreteSøimer
Graphicdesigncover:FeteTyper
MeSH:influenza,publichealthsurveillance,influenzaseason2017-18,riskassessment,influenzavaccine
Citation:DepartmentofInfluenza.Earlyriskassessment:Whattoexpectofthe2017/18influenzaseasoninNorway.Report2017.Oslo:NorwegianInstituteofPublicHealth,2017.
What to expect of the 2017/18 influenza season in Norway • Norwegian Institute of Public Health
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What to expect of the 2017/18 influenza season in Norway • Norwegian Institute of Public Health
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Tableofcontents
Scope_____________________________________________________________________________ 5
Summaryprospectsforthe2017/18season _____________________________________________ 6
Summaryoftheprevious2016/2017season_____________________________________________ 7
The2017/18seasonthisfar __________________________________________________________ 8Influenza-likeillnessinprimaryhealthcare 8Severeinfluenza 8Laboratoryconfirmedinfluenza 9Geneticcharacterizationsofthevirusesincirculation 12Antiviralsusceptibility 14Vaccine 14
Vaccinematch 14Vaccinedistributionandcoverage 15
Infectioncontrolmeasures 15Pre-seasonpopulationimmunitytoinfluenza,August2017 16
TheNationalSeroepidemiologicalInfluenzaProgramme 16Summaryofoutcomes 16HighseroprevalencestoinfluenzaAvirusesinAugust2017 16LowtomoderateseroprevalencestoinfluenzaBvirusesinAugust2017 18ImmunityagainstanewinfluenzaB/Victoria-lineagehemagglutinindoubledeletionvariant 18
Acknowledgements________________________________________________________________ 19
References _______________________________________________________________________ 20
What to expect of the 2017/18 influenza season in Norway • Norwegian Institute of Public Health
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Scope
ThisreportpresentstheassessmentbytheNorwegianInstituteofPublicHealth(NIPH)ontheinfluenzasituationearlyinthe2017/2018season,andpossiblecharacteristicsoftheupcominginfluenzaoutbreakinNorway.Thereportisbasedondatafromalate-summerserosurvey,early-seasonsurveillancedata,vaccinesalesandexperiencefrompreviousinfluenzaseasons.Thereportismeanttosupportcapacityplanninginthehealthservices,providebackgroundinformationtoinfectioncontrolandotherhealth-careandpublichealthpersonnel,aswellastoprovidein-depthinformationoninfluenzaoutbreaksingeneral.Atthispoint,asthe2017-2018outbreakisbeginningtounfold,itisofparticularinteresttoassessthedifferentcirculatinginfluenzaviruses,theireventualspread,andhowthiswillinfluencetheextentofillness,severeillnessandmortalityinvariousriskandagegroups.ThereportisthisyearwritteninEnglish,sincewepresumethatthepre-seasonimmunityandearlysurveillancedataanalysismaybeofinterestbeyondNorway.
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Summaryprospectsforthe2017/18season
• Influenzaactivityiscurrentlyverylow.Virusdetectionshavestartedtoincreaseearly,butisnotescalatingasfastaslastyear.NoticeableoutbreakactivitybyChristmas/NewYearislikelybutthemainoutbreakmaypeaklater.
• UptonowinfluenzaA(H3N2)detectionshavebeeninmajoritybutB/Yamagatalineagevirusesatpresentappeartobeincreasingmore.InfluenzaA(H1N1)pdm09andB/Victoria-lineagevirusesappeartoplayaminorrolesofar.
• IncreasedpopulationimmunitymeasuredinantibodiesagainstinfluenzaA(H1N1)pdm09andA(H3N2)inbloodsamplescollectedinAugust2017,particularlyinagegroupsimportantforvirusspread,mightlimitcirculationofthesevirusescomparedtothelasttwowinters.AlowerproportionhasantibodiesagainsttheinfluenzaBviruses.
• Theeventualmagnitudeoftheoutbreakcannotbeforecasted.• InfluenzaA(H3N2)andinfluenzaB/Yamagatalineageviruses,ofvariantssimilar
tovirusescirculatinglastwinter,arethemostlikelycandidatesforpredomination.BoththerecentincreaseininfluenzaBandthehighprevalenceofantibodiesagainstA(H3N2)virusesspeakinfavouroftheB/Yamagatavirus.However,itisstilltooearlytotellwhichofthetwowillbeinmajority,andthismayalsocometovarybyregion.
• BoththeA(H3N2)andB/Yamagatalineagevirusestendedtoinfecttheelderlylastwinterbutincurrent-seasonearlydatatheelderlyarenotequallyprominentamongtheinfected.However,earlydataonhospitalisedinfluenzacasesindicatethattheseviruseswillmostlikelycausemostdiseaseandsevereoutcomesamongtheelderly.
• ThevaccineeffectagainstthecirculatingH3viruseswillprobablybelowtomoderate.ThevaccineeffectagainstB/Yamagatawillalsoprobablybelowtomoderate,sincethisvirusstrainisnotincludedinthevaccine.However,somecrossprotectionbetweenB/Victoria,whichisincludedinthevaccine,andthecirculatingB/Yamagataisexpected.
• Vaccinationisthebestmeasuretopreventsevereinfluenzainhigh-riskgroups.Sincetheeffectofinfluenzavaccinesvary,useofantiviralsshouldalsobeconsidered,bothforvaccinatedandunvaccinatedpeopleandinparticularforriskgroups.
Influenzaoutbreaksareintheirverynatureunpredictable.TheNIPHmonitorsthesituationcloselyandmayaddupdatestotheassessmentasneeded.Influenzasurveillancedataarepublishedweeklyonwww.fhi.no/influensa.
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Summaryoftheprevious2016/2017season
In2016/2017,theinfluenzaepidemicstartedunusuallyearly.ThemainoutbreakpeakedaroundChristmas/NewYear(Fig.1)andwasdominatedbyinfluenzaA(H3N2),geneticgroup3C.2a.InfluenzaB/Yamagata-lineagevirusesculminatedverylatewithaminorpeakinmid-May,butthetotalnumberofdetectionswaslow.FortheNorwegianpopulationasawhole,lastseason’sinfluenzaepidemicwasofmediumintensity(Fig.1).However,forpeople65yearsorolder,theepidemicwasofextraordinaryintensity.Ahighproportionofelderlyvisitedgeneralpractitionersoremergencyclinicsandseveraloutbreaksinnursinghomeswerereported.Theincidenceofelderlythatwashospitalisedduetoinfluenzawashighercomparedtotheprevioustwoseasons.Theinfluenzaepidemicwasestimatedtohavecausedabout1700excessdeathsattributabletoinfluenza,withmostdeathsoccurringintheelderly.
Lastseasontheapproximatenumberofvaccinedosesusedwas533000doses,ofwhichthemajoritywasusedforpeopleover65years.Thevaccineeffectwasdeemedasmoderateagainstthecirculatingstrains.
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The2017/18seasonthisfar
Influenza-likeillnessinprimaryhealthcare
Sinceweek40/2017,theoccurrenceofinfluenza-likeillness(ILI)inNorwayhasbeenverylow(Fig.1).TheproportionofpatientsdiagnosedwithILIatgeneralpractitionersandemergencyclinicshasslowlyincreasedfrom0.3%inweek43/2017to0.5%inweek48/2017.Todeterminethestartofthisseason’sinfluenzaoutbreak,thresholdvalueshasbeencalculated,usingtheMovingEpidemicMethod(MEM)(1).Thisyear’soutbreakisdefinedtostartwhentheILI%reaches0.80%.Thismeansthataccordingtothismeasure,inweek48/2017,thisseason’sinfluenzaoutbreakhadnotyetstarted.AlmostallcountiesinNorwayhadverylowinfluenzaactivityinweek48,buttheILI%variedbetweenthecounties.Twocounties,OsloandFinnmarkhadbothcrossedtheoutbreakthreshold,withILIproportionsof0.9%,whichindicateslowinfluenzaactivity.
Figure1.Theproportionofpatientsdiagnosedwithinfluenza-likeillness(ILI)atgeneralpractitionersandemergencyclinicsinNorway2012-2017.
DespiteofverylowILIactivitysofar,fromweek40/2017toweek48/2017,twoconfirmedoutbreaksofinfluenzaA-viruswerereportedfromnursinghomes,whichisearlyandindicateslocalinfluenzaviruscirculation.Overall,thesurveillanceresultsfromprimaryhealthcaresuggeststhattheoccurrenceofILIwillcrossthenationaloutbreakthresholdwithinthenextthreetofourweeks.However,thereisstilluncertaintiesabouthowfasttheinfluenzaactivitywillincreaseandwhenthepeakoftheoutbreakisreached.ThepeaknormallyculminateseitheraroundNewYearoraftermid-February(Fig.1).
Severeinfluenza
Fromweek40/2017throughweek48/2017influenzavirushasbeendetectedin84(1.4%)ofthe5924hospitalisedpatientsthathavebeentested.Ofthese,47personshavebeen60yearsorolder.InfluenzaAvirushasbeendetectedin66hospitalisedpatients,whereasinfluenzaBvirushasbeendetectedin18hospitalisedpatients.Eventhoughthe
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numberofhospitalisedpatientsisstilllowerthisseasonwhencomparedwiththenumberofhospitalisationsatthesametimelastseason,theseresultssuggestthatthisyear’sinfluenzaoutbreakmayalsocausemostseverediseaseinpeopleaged60yearsorolder.InfluenzaA(H3N2)andinfluenzaB-Yamagatavirusesarebothknowntocausemostseverediseaseinthisagegroup.Thismeansthathospitalisationsandinfluenzarelatedexcessdeathsareexpectedinthisagegroup,buttheextentdependsonhowwidespreadA(H3N2)becomesanditmaybelimitedbypre-existingimmunity(seesectionaboutpre-seasonpopulationimmunitytoinfluenza,August2017)inthispartofthepopulationsinceaverysimilarH3viruscirculatedwidelyinthisagegroupduringtheoutbreaklastseason.
ThereportingfromtheNorwegianIntensiveCareRegistryofinfluenzapatientsinICUstartedinweek46/2017.Sinceweek46,twoconfirmed(usingICD-10diagnosticcodeJ10)andninesuspected(J11)influenzacasesinICUwerereported.NodeathsofinfluenzapatientsinICUhasbeenreportedsofar.
Sinceweek40/2017throughweek47/2017,noexcessall-causemortalityhasbeenobserved.
Laboratoryconfirmedinfluenza
Theextentoftestingforrespiratorypathogenshasbeenincreasingyearbyyear(Fig.2),andinfluenzatestingistypicallyperformedaspartofabroadertestingscheme.Duringthe2016/17season,outcomesofmorethan160000influenzatestswerereportedtoNIPH.
Figure2.Weeklynumberofspecimenstestedforinfluenzavirus,thisseasonandthepreviousthreeseasons.
BasedondatafromanumberofotherlaboratoriesinNorway,themostfrequentlydetectedpathogenthisautumnhasbeenrhinoviruswithMycoplasmapneumoniaealsobeingwidespreadandotherpathogens,includinginfluenzavirus,beingconsiderablylesscommon.
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Nevertheless,duetotheextentoftesting,thereweresporadicdetectionsofinfluenzavirusesduringeveryweekthroughthesummer,ashasalsobeenthecaseinallrecentyears.AnincreaseofinfluenzaAvirusdetectionsbeganinmid-October(week43)andhascontinuedthroughweek48,butwithaslightdropbothinnumberofpositivesandproportionpositiveinweek47.InfluenzaBvirusdetectionsdidnotincreasemuchuntilitmorethandoubledinweek46,andbyweek48ithasalmostcaughtupwiththeweeklynumberofinfluenzaAdetections.
Figure3.Laboratorydetections,Norway,startof2017-2018season,comparedwithprecedingseasons.Theleft-handpanelshowstheweeklynumberofinfluenzavirusdetections,theright-handpanelshowstheweeklyproportionofinfluenzaviruspositivesamongthosetested.Whereasthetestsensitivityprobablyhasnotchangedduringtheyearscoveredbythegraph,thenumberofspecimenstestedhasrisengradually.
Whencomparingpositivityrateswithpreviousseasons(Fig.3,right-handpanel),thecoursesofarisalignedwithseasonsthatpeakedwellafterNewYear.Therefore,althoughthenumberofinfluenzacasesarealreadyincreasingandhigherthanmostpreviousseasonsatthistimeofyear,itcannotbeconcludedthatactivityisheadingtowardanearlymainpeak.Agradualrisewithaslow-downoverChristmas/NewYearandthenaresumedincreasetowardalatermainpeak,similartoe.g.the2015/2016season,seemsjustaslikely.
Thelaboratorydetectionsdataavailableatthisstagegivenoinformationregardingtheeventualmagnitudeoftheoutbreak.
WhereastherehasbeentwiceasmanyinfluenzaAdetectionsasinfluenzaBsincethestartoftheseason,influenzaBdetectionshaverecentlybeenincreasingmoreandthetypeAdominancehasgraduallybeenlostduringthelastthreeweeks(Fig.4,leftpanel).Ifthistrendcontinues,theinfluenzaBvirusesmaytakepredominanceinthebuild-uptothemainoutbreak.
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Figure4.Weeklyproportionsofinfluenzatype(leftpanel)andinfluenzaAsubtype(rightpanel),startof2017-2018season,Norway.
AmongthesubtypedinfluenzaAviruses(n=181),thestrongpredominanceofA(H3N2)overA(H1N1)appearstobemaintained,andmostoftheA(H1N1)detectionsareconcentratedinsouthwesternNorway.AmongtheinfluenzaBvirusesforwardedtotheNationalInfluenzaCentre(NIC)inNIPHandfurtheridentified,48(96%)havebelongedtotheB/Yamagata/16/1988lineageandonly2totheB/Victoria/2/1987lineage.
Figure5.Laboratorydetections,Norway,startof2017-2018season.Weeklynumberofthedifferentinfluenzavirusesisdisplayedasstackedbars,andinfluenzaviruspositivityratesofsentinelspecimens(two-weekaverages)andalllabtesting,respectively,areshownaslinegraphs.
Basedonthecurrentdata,influenzaA(H3N2)andB/Yamagata-lineagevirusesarethetwothataremost likelytopredominate,withA(H1N1)pdm09andB/Victoria-lineageviruseslikelytoplayalesserroleinNorwaythiswinter.
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Toelucidateageprofilesforthedifferentviruses,thenumberofdetectionsperagegroupwasdividedbythepopulationsizeoftheagegroup,thusproducingseasonalincidencesofdetections(Fig.6).
Figure6.Agegroup-specificcumulativeseasonalincidenceofvirusdetections,forinfluenzaA(H1N1)pdm09,A(H3N2),andB/Yamagata-lineage.OnlytwoB/Victoria-lineageviruseshavebeendetectedatthisstage,bothinthe25-59yearsagegroup.Thecumulativenumberofdetectionsrecordedineachagegroupisdividedbytheagegrouppopulationsize,toachievebettercomparabilitybetweenagegroups.Theincidencescannotbecomparedbetweenthedifferentviruses,sincetheextentoftestingforsubtypeandlineagevarieswidely.
Althoughnumbersaresmall,influenzaA(H1N1)casesareskewedmoretowardinfantsthanobservedfortheotherinfluenzaviruses.
TheageprofileforinfluenzaA(H3N2)virusesassumesaW-shapelikelastseason,butlastwintertheincidencefortheelderlywasmuchhigherthanalltheotheragegroupsandthisisnotseennow,atleastnotyet.Thehigherincidenceinelderlylastwinterwasevidentalreadybyweek45/2016,whenthecumulativenumberofH3caseswaslowerthanthepresentdatacollectedthroughweek48/2017.
Similarly,lastwintertheelderlyweremorethantwiceaslikelyaspeopleinotheragegroupstobediagnosedwithinfluenzaB/Yamagata-lineageviruses,andthisisnotapparentsofarthisseason.
Theearly-seasonageprofilesthusmaygivesomehopethattheupcomingseasonmightnotselectivelyaffecttheelderlyinthesamewayasthepreceding2016/2017season.Theagepatternsmaychangeastheoutbreakprogresses.
Geneticcharacterizationsofthevirusesincirculation
Asofweek46,43%(57viruses)ofallinfluenzavirusesreceivedatNICNorwayhavebeenfurthercharacterisedgenetically.AselectionofsequencesisavailableinGISAID(www.gisaid.org).
Asthepreviousseason,theinfluenzaA(H3N2)virusesarepredominatingthestartofthe2017/18season(Fig.7:ClusteranalysisofH3).BothH3N2group3C.2aand3C.2a1virusesarecirculating;however,the3C.2amaingroupofviruseshassofaroutnumberedthe3C.2a1virusesandseemtobemorewidespread.Thesame3C.2aviruseswerealsodominatingthepreviousseasoninNorway,incontrastto3C.2a1virusesinmostofEurope.TheH3N2vaccinecomponentalsobelongstothe3C.2agroupofvirus,butseveral
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3C.2asubcladeshaveemerged,makingthegeneticpictureforH3virusesverycomplex(Fig.7:ClusteranalysisofH3).
Figure7.MaximumparsimonyclusteranalysisoftheHAgeneofNorwegianinfluenzaH3viruswithnorthern3C.2a(2017/18)andsouthern3C.2a1(2018)hemispherevaccineH3virusesasreferences(whitecircles).Virusesarecolour-codedbydefinedgeneticsubgroups.HAaminoacidsubstitutionsdefiningthedifferentgeneticgroupsaregiven(withreferencetoA/Texas/50/2012).
TheNAgeneofthe3C.2avirusesgroupgeneticallytogetherwiththeNAgenesoftheothergroupofH3viruses,the3C.2a1(notshown).Theeffectofthisreassortmentiscurrentlyunknown.
TheinfluenzaB/YamagatavirusesaresimilartothevirusesfromthepreviousseasoninNorwayandgroupgeneticallywithclade3B/Yamagata-lineageviruses(Fig.8).TwosinglerecentvirusesfromdifferentpartsofNorwaystandoutfromtheotherB/Yamagatathisandpreviousseason,possessingtwoaminoacidsubstitutionsinHAcomparedtothevaccinestrain,namelypositionsQ122KandT181A.TheincreaseinB/Yamagatacasesthelastweekscannotbeexplainedbythegeneticanalysisofthecirculatingviruses.
OnlytwoinfluenzaB/Victoriaviruseshavesofarbeendetected,thesehavenotyetbeengeneticallycharacterised.
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Figure8.MaximumparsimonyclusteranalysisoftheHAgeneofNorwegianinfluenzaB/YamagataviruswithnorthernhemispherevaccineB/Yamagatavirus(redcircle)asreference.Virusesarecolour-codedbyvirusesfromthe2017/18season(green)andfromprevious2016/17season(white).KeyHAaminoacidsubstitutionsaregiven.
TheH1N1virusesareallclade6B.1andthelargestgeneticgrouppossessesthefollowingsubstitutions:T72S,S74R,D97N,P137S,S162N,S164T,K163Q,I216TandI295V.
Antiviralsusceptibility
Noresistancetowardsneuraminidaseinhibitorslikeoseltamivirandzanamivirhassofarbeendetectedoutof8H3viruses,9H1virusesand1influenzaBvirusanalysed.
Vaccine
VaccinematchAsthepredominantH3influenzastraininNorwaybelongstothesamegroupofH3virusesastheH3vaccinecomponent,thevaccinewillinducesomeprotectiontowardstheH3viruses.WeexpectvaryinglevelsofprotectionasseveraldifferentsubgroupsofH3virusesareincirculation(2).TheWHOCollaboratingCentrelaboratoryinLondonestimatesthatabout70-80%ofthe3C.2aH3virusescirculatingduringthelastseasonandthesummermonthswillbewellcoveredbythevaccine,and60%ofthe3C.2a1H3viruses(3).TheH1virusesmatchtheH1vaccinecomponent.However,theB/VictoriavirusinthevaccineisnotagoodmatchtowardstheB/YamagatavirusescurrentlycirculatinginNorway,stillsomecross-protectionisexpected.
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TheinfluenzavaccinefortheNorthernhemisphere2017/18containsthreedifferentviruscomponents:
• A/Michigan/45/2015(H1N1)pdm096B.1-likevirus• A/HongKong/4801/2014(H3N23C.2a)-likevirus• B/Brisbane/60/2008-(B/Victoria)-likevirus
VaccinedistributionandcoverageAvailablevaccinesforthevaccinationoftargetsgroups(riskgroupsandhealthcareworkers)(4)aresplitvaccineVaxigrip®2017/18fromSanofiPasteur,andsub-unitvaccineInfluvac®2017/18fromBGPProducts.Bothvaccinesareavailablefortheprivatemarket,inadditiontonasalvaccineFluenzTetrafromAstraZeneca.
AsofseventhofDecemberNIPHhasdistributedover525000vaccinedosesforthetargetgroups.InadditionNIPHandotherwholesalershavedistributednearly113000dosesfortheprivatemarket.Totalvolume:almost638000vaccinesdoses.Thisisanincreaseof90000dosescomparedtolastyear.
AsofsixthofDecember337091personshavebeenregisteredinthenationalvaccineregistrySYSVAKasvaccinatedwiththisseason’svaccine.Themajorityofthem–229952-areover65yearsofage.Thereisacertainlagtimeintheregistrationofsomevaccinations,sotherealnumberofvaccinatedisprobablymuchhigher.
TheinfluenzavaccinecoverageinNorwayremainslow.Nevertheless,ithasincreasedthelastcoupleofyears,especiallyintheelderlyandamonghealthcareworkers.Lastseasonthevaccinecoverageinthegeneralpublicwas10%.Thecoveragewas38%amongtheelderlyand17%inhealthcareworkers.Consideringtheincreaseinvaccinesalesthisseason,itseemsthatthevaccinecoverageingeneralwillbeatleastashighaslastyear’s.Thiswillhopefullycontributetofewerhospitaladmissionsanddeathsduetoinfluenzaamongtheriskgroupsthecomingseason,sinceitwilladdtothepriorimmunityalreadypresentinthepopulation.
Infectioncontrolmeasures
Vaccinationisthemosteffectivepreventivemeasureagainstinfluenza.Sincetheeffectofinfluenzavaccinesvary,useof antivirals shouldbe considered forpatients experiencinginfluenzaillness,particularlyforthosebelongingtoriskgroups.Antiviraltreatmentshouldbeinitiatedasearlyaspossibleafteronsetofsymptoms(preferablywithin48hours),bothfor vaccinated and unvaccinated patients. For patients with severe influenza requiringhospitalisation,treatmentwithantiviralsshouldalsobeconsideredlaterinthecourseofthedisease.
Topreventtransmissionofinfluenza,itisalsoimportanttopracticegoodhandandrespiratoryhygiene.
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Pre-seasonpopulationimmunitytoinfluenza,August2017
TheNationalSeroepidemiologicalInfluenzaProgramme
TheNationalSeroepidemiologicalInfluenzaProgrammeannuallycollectsinAugustabout2000 serum samples during theweeks 31-35 from clinical/microbiological laboratoriescoveringthe19countiesofNorway.Theseanonymisedconvenienceseraareaimedtoberepresentativeof theNorwegianpopulationgeographicallyandbyagecomposition.Thesera are tested by the hemagglutination-inhibition (HI) test to determine the antibodyimmunity to relevant circulating influenzaviruses.HI titres³40against the influenzaAstrainsand³80againstether-treatedinfluenzaBstrainsareconsideredasprotectivelevelsandrecordedasseropositiveintheanalysis.
The2017serumpanelwastestedbyHIagainsttheNorthernhemisphere2017/18seasonalinfluenza vaccine strains (trivalent/quadrivalent). In addition, two recent viruses wereanalysedinHI:A/California/07/2009(H1N1pdm09/X179A),thepreviousH1N1vaccinevirus,andA/Norway/3806/2016,arecentH3N23C.2a.1variant-likevirusbelongingtothesame group of viruses as A/Singapore/MIFIMH-16-0019/2016, the new H3 vaccinecomponentofthe2018influenzavaccinefortheSouthernhemisphere(Table1).
The results are shown in Fig. 9 and Table 1. HI testing is still ongoing and the presentpreliminaryanalysishasbeencarriedoutonasubsetrepresentingapproximately¾ofthecomplete annual panel. Protective immunity from subsequent seasonal vaccination willcomeinaddition.
SummaryofoutcomesTheseroprevalencetobothinfluenzaAvirusesisrelativelyhigh,indicatinggoodprotectiveimmunityagainstthetwoinfluenzaAvaccine-likeviruses.However,newH3N2HAvariantswithmajorantigenicdriftmaygivelessprotectioninthepopulation.Historically,H3N2viruseshavehigherfrequencyofmutationsinHAandmaythushaveahigherpotentialfornewvariantsascomparedtotheH1N1pdm09viruses,whichhaveundergonelittleantigenicchangesincethepandemicin2009.TheseroprevalencetoinfluenzaBvirusesislowtomoderate,asithasbeenthelastfewyears.Thismayindicateapopulationvulnerabilitythathasnotbeenexploitedduringthelastseasons,forreasonsnotwellunderstood.Inaddition,althoughitremainsrarelydetectedandthatapreliminaryanalysissuggestcross-immunityfromrelatedviruses,thenewinfluenzaB/VictoriaHAdeletionvariantmaybereasonforsomeconcern.
HighseroprevalencestoinfluenzaAvirusesinAugust2017TheseroprevalencesagainstbothinfluenzaA(H1N1)-andA(H3N2)-virusesareunusuallyhighinAugust2017andhadincreasedsignificantlyfromAugust2016(Fig9).Thehighestincreaseinprotectiveantibodyimmunity,by22percentagepoints,isseenagainstA(H3N2)withall-agesseroprevalencealmostdoubled.ThisreflectsthedominantcirculationofH3N2vaccine-likevirusestheprecedingseason.Surprisingly,anincreaseinseroprevalencetoA(H1N1)by9percentagepoints(18%relativeincrease)isseeneventhoughveryfewH1N1virusesweredetectedtheprecedingseason.
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ThehighestantibodyseroprevalencestobothH1N1andH3N2virusesareseenin5-14and15-24yearolds(Table1).ThisholdsforboththeH1N1virusestested,A/California/07/2009andA/Michigan/45/2015(clade6B.1),thepreviousseasonandthecurrentseasonH1vaccinevirus,withabout75to80%seropositiveinthesetwoagegroups,i.e.increasesby8and10percentagepointsfrompreviousyear.Additionally,theseroprevalencestoH1N1intheagegroups25-59and60+yearoldsarehigherthanseentheyearbeforewithabout8to10percentagepointsincrease,whileforthe0-4yearoldsthereisadecreaseof8percentagepoints.
ThehighestseroprevalencesagainsttheH3N2vaccinevirusA/HongKong/4801/2014(anH3N23C.2avariant)arealsointhosebetween5-14and15-24yearsoldwith80%and67%.Thisisanincreasefromthepreviousyearby20and33percentagepoints,respectively.TheseroprevalencesfortheotheragegroupsagainstH3N2havealsoincreasedsubstantiallybybetween15to19percentagepointsfromAugust2016.Interestingly,theseroprevalencesinvariousagegroupsagainstarecentnewH3N23C.2a.1-groupvirus,A/Norway/3806/2016,aresimilartotheprevalencestoA/HongKong/4801/2014-likevirus.AnH33C.2a.1-variantvirus(A/Singapore/INFIMH-16-0019/2016)wasrecentlyselectedastheH3N2vaccinecomponentfortheSouthernhemisphere2018season.
Figure9.InfluenzaseroprevalenceinAugust2017.All-agespercentageofserawithprotectiveHI-titreagainsttheH1N1,H3N2,B-VictoriaandB-Yamagataviruscomponentsofthe2017/2018Northernhemispheretrivalent/quadrivalentinfluenzavaccine(Bluecolumns,preliminarydata).Forcomparison,thecorrespondingseroprevalenceinAugust2016isalsoshown(Orangecolumns).
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Table1.Agegroupseroprevalencestothe2017/2018influenzavaccinecomponentsandtworecentcirculatingvariants(H1N1pdm09andH3N23C.2a.1)ofseracollectedinAugust2017.
Virus
Agegroup(yrs)
0-4 5-14 15-24 25-59 60-99
A(H1N1)pdm09A/Cal/07/2009(X179A) 24%* 78% 81% 52% 46%A(H1N1)A/Michigan/45/2015(6B.1)(V) 24% 74% 81% 49% 41%A(H3N2)A/HongKong/5738/2014(3C.2a)**(V) 33% 80% 67% 35% 42%A(H3N2)A/Norway/3806/2016(3C.2a.1) 31% 80% 74% 40% 46%B(Vic)B/Brisbane/60/2008(V) 8% 30% 22% 12% 22%B(Yam)B/Phuket/3073/2013(V4) 4% 24% 34% 21% 17%
*Percentage of sera with HI titre ≥40 for influenza A virus and ≥80 for influenza B virus. The results arepreliminarydatafromabt.2/3ofthe2017serumpanel.Numberofsamples(n)ineachagegroupare:113,199,222,503,and276.(V):TrivalentvaccinevirusesoftheNorthernhemisphere2017/2018vaccine;(V4):thefourthcomponentin4-valentvaccine.**A/HongKong/5738/2014isanA/HongKong/4801/2014-likevirus
LowtomoderateseroprevalencestoinfluenzaBvirusesinAugust2017LesschangesfromAugust2016inseroprevalencesareseenagainstthetwoinfluenzaBlineagesB/VictoriaandB/Yamagata,bothfor‘Allages’andinthevariousagegroups(Fig8).Formostagegroupschangesinseroprevalencesarelessthan+/-5percentagepoints,exceptforthose60yearsandoldertotheB/Victoria-lineagevaccinecomponentB/Brisbane/60/08withanincreaseof11percentagepoints.
ImmunityagainstanewinfluenzaB/Victoria-lineagehemagglutinindoubledeletionvariantDuringlastseason,aB/Brisbane/60/08(B/Victoria-lineage)hemagglutinin(HA)doubledeletionvariantwasidentifiedintheUSandNorwayaswellassomeothercountries,causingseriousconcernforlackofimmunitytothisnewB/Victoria-lineagevariantvirusinthehumanpopulationasindicatedbyantigeniccharacterizationusingmonospecificferretantisera.However,preliminaryHIanalysisusingpre-2016/17humanserafromourannualserumcollectionmayindicatethatthereissomelevelofcross-reactiveantibodiesinthepopulationtothisnewvariant(datanotshown).Furthermore,thisvarianthasnotbeenseeninincreasednumbersduringthe2017SouthernHemisphereseasonandthus,theriskformajorspreadofthisvirusvariantinitscurrentformmaybelowerthaninitiallyfeared.However,influenzaBvirusestendtocirculatelaterinseasonandifadditionalmutationsintheHAtakeplace,theexistingcross-immunityinthehumanpopulationmaygivelessprotection.
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Acknowledgements
TheNIPHwouldliketoexpressourgratitudetoallmedicaldoctorsandotherstaffattheregulargeneralpractitioneroffices,emergencyclinicsandmicrobiologicallaboratoriesthathavecontributedtothesurveillancebysendingsamplesanddata.WearealsoverygratefulforthecontributionofdatafromtheNorwegianIntensiveCareRegistry,andtothehospitalsandnursinghomesfornotifyingoutbreaksinVESUV.
WewouldalsoliketothankallthehealthcareworkersthathaveorganisedthetargetgroupvaccinationandcontributedtotheregistrationofinfluenzavaccinationsinSYSVAK.
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References
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2. Sullivan,S.G.,etal.,Lowinteriminfluenzavaccineeffectiveness,Australia,1Mayto24September2017.EuroSurveill,2017.22(43).
3. WORLDWIDEINFLUENZACENTRE-WHOCCforReference&ResearchonInfluenza,TheFrancisCrickInstitute:ReportpreparedfortheWHOannualconsultationonthecompositionofinfluenzavaccinefortheSouthernHemisphere2018.https://www.crick.ac.uk/media/393884/crick_sh2017_vcm_report_to_post.pdf
4. Recommendedriskgroupsforinfluenzavaccinationseason2017-2018.https://www.fhi.no/sv/influensa/influensavaksine/influensavaksine-risikogrupper/
Published by The Norwegian Institute of Public Health December 2017P.O.Box 4404 NydalenNO-0403 OsloTel: + 47-21 07 70 00
The report can be downloaded as pdf at www.fhi.no/en/publ/