w w w . e l s e v i e r . p t / r p s p
Original
Article
Association
between
chronic
stress
and
immune
response
to
influenza
vaccine
in
healthcare
workers
Ema
Sacadura-Leite
a,b,c,∗,
António
Sousa-Uva
b,c,
Helena
Rebelo-de-Andrade
d,e,
Sancha
Ferreira
a,
Regina
Rocha
aaOccupationalHealthDepartmentofHospitaldeSantaMaria/CHLN,Lisbon,Portugal bNationalSchoolofPublicHealth/NewUniversityofLisbon,Lisbon,Portugal
cCMDT–CentrodeInvestigac¸ãodaMaláriaeDoenc¸asTropicais–PublicHealth,Lisbon,Portugal dNationalInstituteofHealth,INSA,Lisbon,Portugal
eFacultyofPharmacy,UniversityofLisbon,Lisbon,Portugal
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received15April2013 Accepted27September2013 Availableonline19December2013
Keywords: Antibodyresponse Healthcareworkers Influenzavaccine Psychologicalstress
a
b
s
t
r
a
c
t
Introduction:Chronicstresscaninfluenceimmuneresponsetovaccines.Healthcareworkers areexposedtostressorsandbiologicalhazards,thehealtheffectsofwhichmaybeprevented throughvaccination.
Objectives:Thisstudyaimstoevaluate theassociationbetweenstressinnursesand:(1) insufficientresponsetoinfluenzavaccine,assessedonemonthaftervaccination(T1);(2)
thedropinhaemagglutination-inhibition(HAI)antibodies(ab)sixmonthsaftervaccination (T6).
Methods:Anestedcase–controlstudywascarriedoutwith136healthyhospitalnurses. Individualinterviews,theGeneralHealthQuestionnaire(GHQ12)andMaslachBurnoutInventory
(MBI-HSS)wereappliedinordertodeterminethepresenceofstress,usingthetriangulation methodatthebeginningofthestudy(T0).Influenzavaccinewasadministeredandtitres
ofHAIaboveeachstraincomposinginfluenzavaccinebeforevaccination(T0),atT1andT6
wereassessed.
Results:Therewasnostatisticallyrelevant(5%)relationshipbetweenstressandthe insuffi-cientimmuneresponsetothevaccineatT1.Nevertheless,therewasanassociationbetween
stressandthedropinHAIabAH1atT6,whenweassessedstressbythetriangulationmethod
usinganinterview(p=0.006),GHQ12(p=0.045)andcombinationofcriteria(p=0.001),even
aftermultivariateanalysis(respectively,p=0.01,p<0.05andp=0.002).Theoddsratioswere, respectively,3.64,2.73and5.22.
Conclusions:Theassociationwefound,betweenchronicstressandthedropinHAIabat T6, corroboratesthehypothesis thatstresscannegatively influenceimmune response.
Therefore,itseemsreasonableto considerthis issuewhen weimplementvaccination programmesforhealthcareworkers.
©2013EscolaNacionaldeSaúdePública.PublishedbyElsevierEspaña,S.L.Allrights reserved.
∗ Correspondingauthor.
E-mailaddress:ema.leite@chln.min-saude.pt(E.Sacadura-Leite).
0870-9025/$–seefrontmatter©2013EscolaNacionaldeSaúdePública.PublishedbyElsevierEspaña,S.L.Allrightsreserved.
Stresse
crónico
e
a
imunidade
à
vacina
contra
a
gripe
em
profissionais
de
saúde
Palavras-chave:
Anticorpos
Profissionaisdesaúde Vacinacontraagripe Stresse
r
e
s
u
m
o
Introduc¸ão: Ostressecrónicopodeinfluenciararespostaimunitáriaàvacinac¸ão.Os profis-sionaisdesaúdeestãoexpostosastressoresdenaturezaprofissionaleaindaaagentes biológicoscujosefeitospoderãoserprevenidospelavacinac¸ão.
Objetivos: Estudaraassociac¸ãoentreapresenc¸adestressee(1)a“insuficiente”resposta imunitáriaàvacinacontraagripe,avaliadaummêsapósavacinac¸ão(T1);(2)areduc¸ãodos
títulosdeanticorposdirigidosàshemaglutininas(HAI)seismesesapósavacinac¸ão(T6).
Métodos: Realizou-seumestudocaso-controloincorporadonumestudodecoortescoma participac¸ãode136enfermeiroshospitalaressaudáveis.Realizaram-seentrevistas individu-aiseaplicaram-seosquestionáriosTheGeneralHealthQuestionnaire(GHQ12)eMaslachBurnout
Inventory(MBI-HSS)paradeterminac¸ão da presenc¸a destresse crónicopelo métododa triangulac¸ão,noiníciodoestudo(T0).Foiadministradaavacinacontraagripee
determinou-seostítulosdeHAIdirigidosacadaestirpecomponentesdavacinacontraagripe,antesda vacinac¸ão(T0),emT1eemT6.
Resultados: Nãoseencontrouassociac¸ãosignificativa(5%)entreapresenc¸adestressea “insuficiente”respostaàvacinacontraagripeemT1.Contudo,encontrou-seumaassociac¸ão
entreapresenc¸adestresseadiminuic¸ãodotítulodeHAIdirigidosàestirpeA(H1N1)emT6
quandoseavaliouapresenc¸adestressepelométododatriangulac¸ãousandoaentrevista (p=0,006),oGHQ12(p=0,045)eacombinac¸ãodostrêscritérios(p=0,001),quesemanteveapós
análisemultivariada(respetivamentep=0,01,p<0.05ep=0.002).Osoddsratioajustadosforam de3,64,de2,73ede5,22.
Conclusões: Aassociac¸ãoencontradaentreapresenc¸adestressecrónicoeareduc¸ãodo títulodeHAIemT6vemapoiarahipótesedequeostressepoderáinfluenciar
negativa-menteamanutenc¸ãodostítulosdeanticorpos,mesmoemindivíduosadultosnãoidosos. Assim,parecerazoávelconsideraresteaspetoquandosepretendeimplementarprogramas devacinac¸ãodirigidosaprofissionaisdesaúde.
©2013EscolaNacionaldeSaúdePública.PublicadoporElsevierEspaña,S.L.Todosos direitosreservados.
Introduction
Healthcareworkersareexposedtomanystressors,someof
themrelatedwithorganisationalworkconditionsandothers, morespecifictothisprofession,relatedwiththeiractivityof caringfortheill.1–3
Chronicstressandburnout seemtobeverycommon in
nurses.4–6 Forexample,López-Castilloandcolleaguesfound
highlevelsofemotionaldisturbancedeterminedbythe Gen-eralHealthQuestionnaire(GHQ28)in39%ofhospitalnurses.7
Amongstthe consequencesofchronicdistress,whether
theyare related or not withwork, are the possibleeffects
on the immune system, including effects on the immune
responsetovaccination.
Healthcareworkersarestronglyadvisedtobevaccinated againstinfluenzainordertoprotectthemselvesagainstthe disease,reducestaff absenteeismandminimisethe riskof nosocomialtransmissionto the patientsthey takecare of. Vaccinationisapossiblemodelforimmuneresponse,
test-ingmostlythehumoralimmuneresponse.Vaccinatedpeople
developantibodies (ab) that bind and neutralise the virus, inmostcasesabagainstthesurfaceglycoprotein hemagglu-tinin.Thoseabcanbeusedasmarkersofprotectionagainst thedisease,8causedbystrainsthataresimilartothevaccine
composition.
According to meta-analysis by Segerstrom and Miller,
chronicexposuretostressorssuchastakingcareofspouses
with dementia, unemployment and suffering from
physi-cal disability is associated with a smaller ab response to influenza vaccine.9 Somereviewsalsosuggest thatchronic
stressisassociatedwithasmallerabresponsetoinfluenza vaccine.10–12
Generally speaking, studies evaluating the association
between chronicstress and immuneresponse toinfluenza
vaccine showed relatively consistent results inold people. In those people, chronic exposure tostressors was associ-atedwithchronicanxietyandsymptomsofdepressionanda lowerresponsetoinfluenzavaccine,incomparisontoa con-trolgroup.13–17
Theuseofastandardizeddoseofantigenwhichpromotes
agoodimmuneresponseinmostadults,couldmakeit
dif-ficultthedetectionoftheinfluenceofchronicstressinthe
immune responsetovaccinationinyounger adults,witha
robustimmunesystem.
Olderpeoplehaveaweakerimmunesystem,relatedwith
age, so this could be an explanation for the greater
con-sistencyofresultsshowinga negativeassociation between
chronic stress and immune response to vaccines inthem.
Vedharaandcolleaguesdidnotfindanyassociationbetween
taking care of spouses with multiple sclerosis and ab
However,thoseadultsshowedsimilarstresslevelsasthe con-trolgroup.
In younger adults, such as university students, some
studies19–22 found an association between stress,
charac-terised in different ways, and the immune response to
influenzavaccine(assessedbyabtitresorbyresponserate) onemonthaftervaccination.However,otherstudiesdidnot findthatassociation.23–25
Some of the studies found an association between
stress and a drop in ab titres assessed 4–6 months after
vaccination,19–23,25evenintheyoungestadults.Thedropin
theabtitresassociatedwithstresswasonlyobservedagainst onestrainofvaccinecomponents,suggestingthatdifferent exposuresor differentpastvaccinationscanberesponsible forthoseresults.
Inanoccupationalcontextofhealthcaresettings,where healthcareworkersareinthelabourmarket(andare there-forenotveryold),butaresimultaneouslyexposedtochronic stressorsandbiologicalriskhazards,itseemsimportantto studytheinfluenceofstressonimmuneresponsetoinfluenza vaccine.
Therefore, this study analyses the association between
stressinnursesand:(1)insufficientresponsetoinfluenza vac-cine,assessedonemonthaftervaccination(T1);(2)thedrop
ininfluenza aemagglutination-inhibition (HAI) abtitres six monthsaftervaccination(T6),ascomparedtoonemonthpost
vaccinationHAIabtitres.
Materials
and
methods
Studydesignandparticipants
Thestudywasanestedcase–controlstudy,conductedoversix monthsinauniversityhospitalduringthe2007/2008influenza season.Subjectswerehospitalnurseswhowerenottakingany regularmedication,includingdrugsthatcouldaffect immu-nity(suchascancertherapydrugsorcorticosteroids).Theydid nothaveanymedicalconditionthatcouldaffecttheimmune responseandtheyalsohadnomajorsurgeryinthepreceding threemonths.Theydidnothaveahistoryofdrug consump-tionoralcoholconsumptiongreaterthan10unitsperweek, nordid theyhandlecitotoxic drugs orwork regularly with ionisingradiation(n=136).Thehospital’sEthics Committee approvedthestudyandalltheparticipantssignedtheir agree-menttoparticipatinginit.
One-monthandsix-monthdrop-outcriteria:
• clinical diagnosis of medical condition that may affect
immuneresponseafterthebeginningofthestudyortaking anyregularmedicationthatcanaffectimmunity(assessed byinterview,atT1andT6);
• workplacechangeswithregularexposuretoionising radia-tionsorcitotoxicdrugshandling;
• clinical influenza symptoms with virus identification in
nasalororopharyngealswab,duringthesixmonthsofthe study;
• ariseinHAIAbtitretoA(H1N1),A(H3N2)orBstrainssix
monthsaftervaccination,ascomparedwiththetitres mea-suredonemonthaftervaccination.SuchariseinHAIAb
titresuggestsanexposuretoinfluenzastrainsduringT1and
T6insteadofadelayedresponsetothevaccine.
Stressassessment
Structuredindividualinterviewswereconductedatthe begin-ningofthestudy(T0)inorderto:
• identify socio-demographic characteristics and possible
confoundable variables related with immunity (physical
exercise,nutritionalparameters,nutritionalsupplements,
hours of sleep per day, smoking habits, shiftwork) and
influenzavaccinationhistory;
• identifywork-relatedandnon-work-relatedstressors,using aLikertscalefrom1to5;
• assessperceivedstress,usingaLikertscalefrom1to5; • identify stress-related behavioural changes or
psychoso-maticsymptoms.
We also applied the Portuguese versions of the General
Health Questionnaire (GHQ12) and Maslach Burnout Inventory
(MBI-HSS orMBI) exhaustion scale atthe beginning ofthe
study(T0).AlfaCronbachforthosescaleswas0.855and0.874
respectively.
Inordertoassessthepresenceofchronicstress,weapplied
the triangulation method at T0, as suggested by Cox and
colleagues,26infourdifferentways:
• throughinterviews:weaccepted thepresenceofchronic
stress using interviews if therewere identified stressors classifiedas4or5,plusperceivedstressclassifiedas4or5, plusatleastonebehaviouralchangeoronepsychosomatic symptomstress-related;
• throughGHQ12:weacceptedthepresenceofchronicstress
usingGHQ12iftherewereidentifiedstressorsclassifiedas4
or5,plusGHQ12higherthan2,plusatleastonebehavioural
changeoronepsychosomaticsymptomstress-related;
• throughMBI:weaccepted thepresenceofchronicstress
usingMBIiftherewereidentifiedstressorsclassifiedas4or 5,plusMBIexhaustionscalehigherthan24,plusatleastone
behaviouralchangeoronepsychosomaticsymptom
stress-related;
• combinationofcriteria:weacceptedthepresenceofstress usingcombinationofcriteriaiftherewasstressusing inter-viewand stressusingGHQ12 orif therewasstressusing
interviewandstressusingMBIexhaustionscale.
Vaccinationandlaboratoryprocedures
Venous blood was drawn at three stagesbetween October
2007andApril2008:(i)immediatelybeforeinfluenza vacci-nation(T0);(ii)onemonthfollowingimmunisation(T1);and
(iii)sixmonthsafterT0(T6).
The samples rested 1hat ambient temperature
follow-ingcentrifugationat3500rpmfor10min.Serawerestoredat −20◦Cuntilused.AllthesamplesdrawnatT0,T1andT6were
processedatthesametimeandunderthesameconditions. Acommerciallyavailable2007/2008trivalentinfluenza
vac-cine,withtherecommendedcompositionforthatseasonin
deltoidmuscle,duringOctober.Allthevaccinesbelongedto
thesamegroup(AFLUA290AD).
Haemagglutinationinhibitionreactionwasusedtoassess specificHAIabtitreagainstinfluenzaA(H1N1),A(H3N2)and
Bstrains included inthe influenza vaccine, in accordance
withtheWorldHealthOrganisation’smanual.27Immediately
beforethelaboratorialprocedures,theseraweretreatedbya
Receptor-DestroyingEnzyme(RDE)inordertoremoveunspecific agglutininsandinhibitors.
The reference antigens were diluted to obtain 4 units
against haemmaglutinin per 25l and incubated with the
treated sera samples. Erythrocytes were then added to
thefluid.
HAIAbtitrecorrespondedtotheinverseofthelastdilution
ofserum that completelyinhibited haemagglutination. We
usedprogressivedilutions,startingwith1:10upto1:20.480. Theserologicalparametersobtainedwere:
• HAI Ab titre against influenza A(H1N1), A(H3N2) and B
strainsincludedininfluenzavaccine,before(T0)andafter
vaccination(T1andT6);
• riseinHAIAbtitreagainstinfluenzaA(H1N1),A(H3N2)andB
strainsincludedininfluenzavaccine,assessedonemonth
after vaccination(comparedtoHAI Abtitreimmediately
beforevaccination);
• dropinHAIAbtitreagainstinfluenzaA(H1N1),A(H3N2)and
Bstrainsincludedininfluenzavaccine,betweenT1andT6.
Definitions
ForanalysisatT1andatT6,wedefinedthefollowinggroups:
respondersatT1(onemonthaftervaccination):participants
thatshowed, atT1,atleastafourfold riseinHAI abtitre
comparedtothetitrebeforevaccination;
non-respondersatT1(onemonthaftervaccination):
partic-ipantsthatdidnotshow,atT1,afourfoldriseinHAIabtitre
comparedtothetitrebeforevaccination;
HAIabtitredropgroupatT6(sixmonthsaftervaccination):
participantswithatleastafourfoldriseinHAIabtitreatT1,
butwhoshowedadropinHAIabtitreatT6,ascomparedto
HAIabtitreatT1;
nochangeinHAIabtitregroupatT6(sixmonthsafter
vac-cination):participants withatleastafourfold rise inHAI abtitreatT1, butwithnochangeinHAIabtitreatT6, as
comparedtoHAIabtitreatT1.
Statisticalanalyses
Fordichotomousvariables,weusedtheQui-squareandFisher exacttestsanddeterminedtheoddsratio.
Fornumericalvariables,weusedtheKolmogorov–Smirnov
andShapiro–Wilkteststoassessnormaldistributionin non-respondersandresponders(T1)andintheHAIAbtitredrop
groupandnochangeinHAIAbtitregroup(T6).
For normal distributions, the T Student test was used
to compare means, and the Levene test to assess variance
homogeneity. For no normal distributions, we applied the
Mann–Whitneytesttocomparemedians.
Wealsousedthemultivariateanalysisanddeterminedthe adjustedoddsratiofortheconfoundingvariables.
Weconsideredastatisticalsignificanceof5%.Alltestswere runintheStatisticalPackageforSocialSciences–SPSS®software,
version14.0forWindows.
Results
Westudied136nurses,mostofwhomwerefemale(83.8%),
Caucasian(96.3%)anddidnotsmoke(77.9%).Theiraverage agewas33andthemedianagewas29(22–63yearsold).Only oneparticipantwasmorethansixtyyearsofage.
Morethanonehalfoftheparticipantshadbeengivenan influenzavaccineshotatleastoneofthefourseasonspriorto thebeginningofthestudy(52.9%),mostlyintheyear imme-diatelybefore(44.1%).Nursesincludedinthestudyworked mostlyonashiftworkbasis(70.6%),hadacorporalindexmass (kg/m2)between18.5and24.9(72.1%)andsleptatleast7hper
day(66.2%).Themajoritydidnottakevitaminsupplements (86.8%)orfishoil(98.5%).Only54.4%didregularphysical exer-ciseand46.3%ateyogurtdaily.
Associationbetweenchronicstressandnon-responders atT1
Onemonthaftervaccination(T1),wedidnotfindany
associ-ation ofstatisticalsignificancebetweennon-respondersfor A(H1N1)virus strain included inthe influenza vaccine and
thepresenceofchronicstressatT0,assessedinfour
differ-ent ways.Similarly,there wasalsono associationbetween non-respondersforA(H3N2)ornon-respondersforBstrains
includedintheinfluenzavaccineandchronicstressatT0.To
simplifythetable,wenamedrespondersornon-responders
forA(H1N1)andforA(H3N2)asrespondersornon-responders
AH1andAH3respectively(Table1).
Aemagglutination-inhibitionantibodiestitresatT0in respondersandnon-respondersatT1
UsingtheKolmogorov–SmirnovandShapiro–Wilktests,wefound thatthereisnonormaldistributioninnon-responders and
responders at T1 for the considered continuous variables
(p<0.001). Therefore, we applied the Mann–Whitney test to comparemediansbetweenHAIabtitresatT0inresponders
and non-responders at T1. We found that non-responders
AH1 atT1 had significantly higherHAI abAH1 titresatT0
than respondersAH1atT1.Thesamehappenedwith
non-respondersAH3atT1 andnon-respondersBatT1,whohad
significantlyhigherHAIAH3titresatT0andHAIBtitresatT0
thanthecorrespondingresponders(Table2).
Associationbetweenchronicstressanddropin aemagglutination-inhibitionabtitresatT6
AtT6(sixmonthsaftervaccination),thepresenceofstressin
theHAI abAH1 titredropgroupwashigherthanintheno
changeinHAIabAH1 titregroup,whenweassessedstress
byalltheconsidereddifferentways,beingstatistically signi-ficativewhenweassessedthepresenceofchronicstressby
Table1–Stressinnon-respondersandinrespondersAH1,AH3andBatT1. HAIabgroupsatT1 Chronicstress
assessment Stressin non-respondersatT1 Stressin respondersatT1 Statisticalanalysis (Qui-squaretest) n(%) n(%) OR(95%CI) p AH1(n=135) Non-responders:45 Responders:90 Stress(interview) 28(62.2) 46(51.1) 1.575(0.759–3.272) 0.221 Stress(GHQ12)a 19(42.2) 44(48.9) 0.764(0.371–1.572) 0.464 Stress(MBI)b 16(35.6) 36(40.0) 0.828(0.394–1.738) 0.617
Stress(combinationofcriteria)c 20(44.4) 41(45.6) 0.956(0.466–1.963) 0.903
AH3(n=136) Non-responders:50 Responders:86 Stress(interview) 27(54.0) 47(54.7) 0.974(0.484–1.961) 0.941 Stress(GHQ12)a 20(40.0) 43(50.0) 0.667(0.329–1.351) 0.259 Stress(MBI)b 15(30.0) 37(43.0) 0.568(0.271–1.190) 0.132
Stress(combinationcriteria)c 20(40.0) 41(47.7) 0.732(0.361–1.483) 0.386
B(n=135) Non-responders:59 Responders:76 Stress(interview) 31(52.5) 43(56.6) 0.850(0.429–1.683) 0.640 Stress(GHQ12)a 24(40.7) 39(51.3) 0.651(0.327–1.293) 0.219 Stress(MBI)b 22(37.3) 30(39.5) 0.912(0.453–1.836) 0.796
Stress(combinationofcriteria)c 24(40.7) 37(48.7) 0.723(0.364–1.437) 0.354
OR–oddsratio;95%CI–95%confidenceinterval.
a GeneralHealthQuestionnaire(GHQ 12). b MaslachBurnoutInventory(MBI). c Stress(interviewandGHQ
12)orstress(interviewandMBI).
triangulationmethodatT0usinginterviews,GHQ12andthe
combinationofthethreemethods.Onthecontrary,wedidnot findanystatisticallysignificantassociationbetweenthe oth-ersHAIabtitredropgroupsatT6andthepresenceofchronic
stress(Table3).
Associationbetweenotherpossibleconfoundingvariables andaemagglutination-inhibitionabAH1titredropgroup atT6
Someconditionsthatcanaffectimmunitycouldhavebeen
possibleconfoundingfactors,whenweconsideredthe asso-ciationbetweenstressandtheHAIabAH1titredropgroupat
T6.UsingtheKolmogorov–SmirnovandShapiro–Wilktests,we
foundthatthereisnonormaldistributioninHAIabAH1titre
dropgroupatT6andinnochangeinHAIabAH1titreatT6for
theconsideredcontinuousvariables(p<0.001).Therefore,we appliedtheMann–Whitneytesttocomparetheirmedians.
Thestatisticalanalysesdidnotfindanysignificant differ-encebetweengroupsatT6forthevariables(continuousand
dichotomous)takenintoconsideration(Table4).
Multivariateanalysisandadjustedoddsratiosforstress, ageandaemagglutination-inhibitionabAH1titresatT0 andT1consideringaemagglutination-inhibitionabAH1 titredropgroupatT6
Stress–assessedbyinterview,GHQ12orusingthecombination
ofthethreemethods–wastheexclusivevariableassociated withHAIabAH1titredropgroupatT6,butwealsotooktheage
variableintoconsiderationinthemultivariateanalysis.That
optionwasmadebecauseageisastrongfactorinfluencing
immunityand,inthesimpleanalysis,themediandifference betweengroupswouldbedifferentifweconsidereda confi-dencelevelof90%(insteadof95%).
Furthermore,BeyerandcolleaguesshowedthatbasalHAI ab AH1 titres influenceHAI abAH1 titres onemonthafter
Table2–HAIantibodiesAH1,AH3andBtitresatT0innon-respondersandinrespondersAH1,AH3andBatT1. HAIantibodiesatT0 Non-respondersatT1 RespondersatT1 Statisticalanalysis(Mann–Whitneytest)
Md(min–max) Md(min–max) Mddifferences p
HAIabAH1titresatT0in non-respondersAH1(n=45) andrespondersAH1(n=90)at T1 640.0(80–10,240) 20.0(10–1280) 620.0 <0001 HAIabAH3titresatT0in non-respondersAH3(n=50) andrespondersAH3(n=86)at T1 160.0(10–5120) 20.0(10–1280) 140.0 <0001 HAIabBtitresatT0in non-respondersB(n=59) andrespondersB(n=76)atT1 160.0(20–10,240) 60.0(10–640) 100.0 <0001 Md-median.
Table3–StressinHAIantibodiestitredropgroupandinnochangeinHAIAbtitregroupAH1,AH3andBatT6. HAIabgroupsatT6 Chronicstress
assessment
StressinHAIabtitre dropgroupatT6
Stressinnochangein HAIAbtitregroupatT6
Statisticalanalysis (Qui-squaretest)
n(%) n(%) OR(95%CI) p
AH1(n=88) HAIabtitredrop group:57 NochangeinHAIab titregroup:31 Stress(interview) 36(63.2) 10(32.3) 3.600(1.427–9.084) 0.006 Stress(GHQ12)a 33(57.9) 11(35.5) 2.500(1.012–6.176) 0.045 Stress(MBI)b 25(43.9) 10(32.3) 1.641(0.656–4.104) 0.288 Stress(combination ofcriteria)c 34(59.6) 7(22.6) 5.068(1.875–13.70) 0.001 AH3(n=81) HAIabtitredrop group:48 NochangeinHAIab titregroup:33 Stress(interview) 25(52.1) 21(63.6) 0.621(0.251–1.539) 0.302 Stress(GHQ12)a 26(54.2) (51.5) 1.112(0.458–2.703) 0.814 Stress(MBI)b 20(41.7) 16(48.5) 0.759(0.311–1.851) 0.544 Stress(combination ofcriteria)c 23(47.9) 18(54.5) 0.767(0.315–1.865) 0.558 B(n=76) HAIabtitredrop group:51 NochangeinHAIab titregroup:25 Stress(interview) 26(51.0) 17(68.0) 0.489(0.179–1.335) 0.160 Stress(GHQ12)a 27(52.9) 12(48.0) 1.219(0.468–3.177) 0.686 Stress(MBI)b 17(33.3) 13(52.0) 0.462(0.174–1.226) 0.118 Stress(combination ofcriteria)c 22(43.1) 15(60.0) 0.506(0.191–1.339) 0.167
OR–oddsratio;95%CI–95%confidenceinterval.
a GeneralHealthQuestionnaire(GHQ 12). b MaslachBurnoutInventory(MBI). c Stress(interviewandGHQ
12)orstress(interviewandMBI).
Table4–Variablesdistribution(stressnotincluded)inHAIabAH1titredropgroupatT6andinnochangeinHAIabAH1
titregroupAH1atT6.
Variables HAIabAH1titredrop
groupatT6(n=57)
NochangeinHAIab AH1titregroupatT6
(n=31)
Statisticalanalysis(Fishertestor Qui-squaretestorMann–Whitney
test)
n(%) n(%) OR(95%CI) p
Malegender 5(8.8) 7(22.6) 0.330(0.095–1.145) 0.103a
Caucasian 53(93.0) 31(100) 0.631(0.536–0.743) 0.293a
Shiftwork 35(61.4) 23(74.2) 0.553(0.211–1.453) 0.250a
Dailysleephours<7 20(35.1) 8(25.8) 0.643(0.244–1.699) 0.372b
Smokers 10(17.5) 9(29.0) 0.520(0.185–1.461) 0.211b
Vitaminsupplements 10(17.5) 4(12.9) 1.436(0.410–5.025) 0.762a
Fishoilconsumption 0(0.0) 0(0.0)
Dailyconsumptionofyogurts 27(47.4) 15(48.4) 0.960(0.400–2.304) 0.927b
Noregularphysicalactivity 29(50.9) 11(35.5) 1.883(0.765–4.634) 0.166b
Pastinfluenzavaccine 17(29.8) 12(38.7) 0.673(0.268–1.687) 0.397b
Influenzavaccineat2006 14(24.6) 11(35.5) 0.592(0.229–1.533) 0.278b
HAIabAH1atT0≥40 25(43.9) 17(54.8) 0.643(0.267–1.551) 0.325b
Variables HAIabAH1titredrop
groupatT6(n=57)
NochangeinHAIab AH1titregroupatT6
(n=31)
Statisticalanalysis(Fishertestor Qui-squaretestorMann–Whitney
test)
Md(min–max) Md(min–max) Mddifferences p
Age 31.0(23.0–63.0) 26.0(22.0–56.0) 5.0 0.072c
Bodyindexmass 22.7(17.7–37.8) 22.0(18.0–37.5) 0.7 0.793c
HAIabAH1titresatT0 20.0(10–640) 40.0(10–1280) −20.0 0.276c
HAIabAH1titresatT1 1280.0(40–20,480) 1280.0(160–20,480) 0.0 0.265c
Md–median.
a Fishertest. b QuiSquaretest. c Mann–Whitneytest.
Table5–Multivariedanalysis(multiplelogisticregression)forstress(assessedbytriangulationmethodusingGHQ12,
usinginterviewandusingthecombinationofthethreemethods)inHAIabAH1titredropgroupatT6consideringage,
HAIabAH1titresatT0andatT1.
Chronicstressassessment Consideredvariablesin multivariedanalysis Statisticalanalysis (multiplelogistic regression) AdjustedOR(95%CI) p GHQ12a Age 1.038(0.989–1.089) 0.134 Stress 2.733(1.039–7.186) 0.042 HAIabAH1atT0 0.998(0.995–1.000) 0.100 HAIabAH1atT1 1.000(1.000–1.000) 0.793 Interview Age 1.043(0.994–1.094) 0.083 Stress 3.643(1.371–9.684) 0.010 HAIabAH1atT0 0.999(0.996–1.001) 0.236 HAIabAH1atT1 1.000(1.000–1.000) 0.987 Combination of criteriab Age 1.044(0.994–1.096) 0.087 Stress 5.223(1.828–14.924) 0.002 HAIabAH1atT0 0.999(0.996–1.001) 0.255 HAIabAH1atT1 1.000(1.000–1.000) 0.892
AdjustedOR–adjustedoddsratio;95%CI–95%confidenceinterval.
a GeneralHealthQuestionnaire(GHQ 12). b Stress(interviewandGHQ
12)orstress(interviewandMBI).
vaccination.28Therefore,wealsoconsideredHAIabAH
1titres
atT0andT1inthemultivariateanalysis.
Wefoundthatstress,assessedbytriangulation method
usingGHQ12, usinginterview andusingthecombinationof
thethreemethods,maintainedtheassociationwithHAIab
AH1 titre drop group at T6. The association between HAI
abAH1titredropgroupatT6andtheothersvariablesdidnot
revealanystatisticalsignificance(Table5).
Whenweassessedstressbytriangulationmethodusing
GHQ12,themodelwasstatisticallysignificant(p<0.029)and
suitable,giventhatnullhypothesiswas notrejectedinthe Hosmer–Lemeshowtest(p<0.106).Themodelshoweda valid-ityrateof65.9.
Whenweassessedstressbytriangulationmethodusing
interview,themodelwasstatisticallysignificant(p<0.009)and suitable,giventhatnullhypothesiswas notrejectedinthe Hosmer–Lemeshowtest(p<0.761).Themodelshoweda valid-ityrateof71.6.
Whenweassessedstressbytriangulationmethodusing
thecombination ofthe threemethods,the modelwas
sta-tistically significant (p<0.002)and suitable, giventhat null
hypothesis was not rejected in the Hosmer–Lemeshow test
(p<0.679).Themodelshowedavalidityrateof73.9.
Discussion
and
conclusions
Whenhumanbeingsare exposedtochronicstressors,they
may respond to them with neuroendocrine changes that
includethereleaseofneuropeptides,monoaminesand
hor-mones. Most of those substances are able to change the
immunecellsbehaviour.29
Psychologicalchronicstresscanchangeantibody(ab) pro-ductionandkineticsaftervaccination,inparticularafterthe influenzavaccineisgiventoelderlypeoplewhotakecareof spouseswithdementia.9–12
Various studies of elderly people have found an
asso-ciation betweenexposure toa long-term stressor (such as
dementiaspousecaregiving)andasmallproportionofthem who reachedatleastabHAItitresthatwere fourfoldwhat
they had before flu vaccination, assessedone monthafter
vaccination.13–15Bereavementandmarriageseemtobe
asso-ciatedwithantibodyresponsetoinfluenzavaccinationinthe elderlyaswell.17
In our study, as insome other studies involving young
adults,18,23–25 wedid notfind any association between the
presenceofchronic stress innurses andthe proportionof themthatreachatleastfourtimestheabHAItitrelevelsthey hadbeforefluvaccination.Onthecontrary,otherstudieshave foundanassociationamongperceiveddistress,19lifeevents,20
neuroticism21andloneliness22andtheimmuneresponseto
fluvaccination,assessedonemonthorfiveweeksafter. Itispossiblethatmethodologicalissuescanexplain dis-crepanciesinresultsverifiedinstudieswithyoungergroups, suchas:(1)differentwaysofcharacterisingindependent vari-ables;(2)sampleswithdifferingdemographiccharacteristics anddimensions;(3)differinghistoriesoffluvirusexposure.
Withrespecttothelatterissue,ourstudyfoundthat non-respondershadsignificantlyhigherabHAIAH1N1,AH3N2and
BtitresatT0thanrespondergroups.Therefore,aspostulated
byBeyerandcolleagues,28abHAItitresatT
0,showedtobean
importantconfoundingvariablewhenstudyingthe
relation-shipbetweenstressandimmuneresponsetofluvaccineone
monthaftervaccinationandmustbeconsidered.
Nevertheless,wefoundanassociationbetweenthe pres-enceofchronicstress(measuredinthreedifferentways)anda dropinabHAI(AH1N1)atT6.Otherstudiesalsofoundan
asso-ciationbetweendistress,19,25lifeevents,20lifeeventsweighed
withperceivedstress,23neuroticism,21orloneliness22anda
drop inabHAIfour tosixmonthsaftervaccination.Those associationswerefoundforatleastonestraincomposingthe fluvaccine.
Ourstudyfoundalargeproportionofnurseswithchronic stressintheHAIabAH1titredropgroupatT6,ascompared
tothenochangeinHAIAbAH1titregroupatT6,whenwe
measuredstressbytriangulationmethod,usinginterviewor GHQ12toassessperceivedstress,andusingthecombination
ofthethreemethods(asdescribedinthemethodssection).We didnotfindanystatisticallysignificantassociationwhenwe assessedthepresenceofstressbythetriangulationmethod
but using the MBI exhaustion scale to measure perceived
stress.ApossibleexplanationisthefactthattheMBI exhaus-tionscalemeasuresspecificallywork-relatedstressandthe possibleimmunologicrepercussionsofchronicstressseemto beindependentofthestresssource.
As described in other studies,19–23,25 the association
betweenstressandadropinabHAIatT6 didnotoccurfor
allthevaccinestrainscomponents.
Strainnoveltycan beanimportantfactorinthat analy-sis,asarguedbyotherauthors.15,20Pressmanandcolleagues,
forexample,onlyfoundanassociation betweenstressand
adropinHAIab,fourmonthsaftervaccination,forastrain thatwas notincludedinprevious vaccinationsthe partici-pantsreceived.25Inourstudy,theexclusivestrainthatwas
not included in flu vaccines in the three preceding years
wastheA(H1N1)strain.
InPortugalthepredominantcirculatingstrainswithhigh fluactivitysince1990havebeenA(H3N2)andB.From1990to
thebeginningofthestudy,theA(H1N1)strainwasonly
pre-dominantin2005,simultaneouslywithstrainB,and2005was ayearwithverylowfluactivity.30WealsoknowthatAstrains
undergomoredriftmutationsthanBstains,31sothiscan
con-tributetotheirbeingarelativenoveltyfortheparticipants’
immunesystem.
Finally,inourstudy,theA(H1N1)influenzastrainprovedto
bethemostimmunogenicone,showingariseintheHAIAb
titregeometricmeanof11.1.A(H3N2)andBstrainsshowed
risesof6.2and 4.6times,respectively, betweenT0 andT1.
Itispossiblethatthebestimmunogenicityobservedforthe A(H1N1)strainwasrelatedwiththefactthatsome
partici-pantshadhadaprimaryinfectionwithanA(H1N1)strain,so
theresponsetoA(H1N1)antigenshavebeenmorerobustin
them.32Thatcouldbeafactorthatmayinfluencethe
detec-tionoftheassociationbetweenstressanddropsinHAIabafter aperiodoftime.
Given that our sample was not a randomised sample
becauseitdependedonnursesvoluntarilybeingvaccinated andparticipatinginthestudy,weanalyseddistribution dif-ferencesforsomevariablesintheHAIabAH1titredropgroup
atT6andthenochangeinHAIAbAH1titregroupatT6thatare
notincludedindropoutcriteria.Astherearealotofvariables
forwhichwedonotyetknow iftheycaninfluence
immu-nity,westudiedthosethataremostreferredtointherelevant literature.33
We did not find any differences in the distribution of
thestudiedvariablesinthetwogroupsatT6.Nevertheless,
wedecidedtoincludeabAH1 titresatT0, abAH1 titresat
T1 and age in multiple logistic regression. The reason for
includingthefirsttwovariableswasthestrongsuggestionin literaturethattheycaninfluenceabtitresaftervaccination (immuneresponse),28eventhoughwefoundnoreferencesto
theinfluencetheyhaveonadropintitressixmonthsafter
fluvaccination.Ageisstronglyrelatedwithimmunity33but
wedidnotfindanydifferenceintermsofagebetweenthe
twogroupsconsideredatT6atthesignificancelevelwe
con-sidered(5%).Ifweconsideredasignificancelevelof10%the
result would be different. Hence, we also included age in
themultivariateanalysis.
Afterthemultivariateanalysis,westillfoundan associ-ation withstatistical significance between the presenceof chronicstressandtheHAIabAH1titredropgroupatT6,when
weassessedstressinthreedifferentways,allofthemusing thetriangulationmethod,assuggestedbyCoxandcolleagues, asagoodwayofmeasuringstress.26Therefore,the
relation-shipthatwefoundbetweenchronicstressandadropinHAIab atT6supportsthethesisthatstresscannegativelyinfluence
HAIabtitressomemonthsafterfluvaccinationeveninpeople inadultsundertheageof60.Aswecouldnotice,thisisthefirst study assessingthe associationbetweenchronicstress and immuneresponsetoinfluenzavaccineinhealthcareworkers, whoisanimportanttargetgroupforinfluenzavaccine. There-fore,inanoccupationalhealthenvironment,itisreasonable toconsiderthepossibleinterferenceofchronicstresswithab titreswhenweimplementvaccinationprogrammestoprevent biologicaloccupationalrisks.
Funding
AutoridadeparaasCondic¸õesdeTrabalho(ACT)fundedthe laboratorialevaluationofthestudy.
Conflicts
of
interest
Theauthorshavenoconflictsofinteresttodeclare.
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