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文章导读
以鲍里斯?约翰逊(BorisJohnson)为首相的英国政府将英格兰解封时间推迟了4周，尽管英国是接种疫苗比例最高的前10个国家之一。人们会问:为什么在推广如此成功的情况下还需要延长限制？到目前为止，英国46.8%的人口完全接种了疫苗，64.2%的人接种了一剂冠状病毒疫苗。然而，疫苗并不神是万能的如果有人对我们打喷嚏，它们不能阻止我们暴露在病毒之下，这就是为什么隔离仍然发挥作用。疫苗的确有助于减少病毒扎根的机会和感染后的强度，同时减少传播。到目前为止，仅在英格兰，他们就挽救了人的生命，并阻止了多人住院治疗。但是仍然有可能接种疫苗的人会将病毒继续传播，特别是在超级传播事件和具有高传播性变异病毒。
BorisJohnson’sgovernmentispushingbackthereleaseoflockdownrestrictionsinEnglandbyfourweeks,despitetheUKbeinginthetop10countrieswiththehighestpercentageofvaccinedosesadministered.Reasonably,peopleareasking:whytheneedforprolongedrestrictionswhentherollouthasbeensosuccessful?Whatdoesasafelevelofvaccinationlooklike?
Todate,46.8%ofthepopulationarefullyvaccinatedintheUKand64.2%havereceivedonedoseofacoronavirusvaccine.ThejabsapprovedintheUKusethevirus’sspikeproteintoeducateourimmunesystemsowhenitmeetstherealthing,itcanproduceantibodiesandT-cellsthatrecognisethisspikeandcontroltheinfection.
Afterthefirstvaccination(ornaturalinfection)ittakesacoupleofweekstoexpandtherelevantimmunecells,butthenmemorycellsprotectusfromseverediseaseinfutureinfections.Inpreviouslyinfectedpeople,thefirstvaccinationactslikeabooster,helpingthemretainantiviralimmunityforlonger.Immunologicalmemorydurationdiffersfordifferentviruses,andthisiswhyweneedtomonitorhowlongprotectionlastsfornewvaccinesandviruses,enablingustoworkoutwhenweneedboostervaccinations.
Thesecondvaccinationintwo-doseregimensactstoincreasethepoweranddurationofimmunityafterthefirstjab.Weappreciatethatimmunitymaywaneafewmonthstoayearaftercoronavirusinfection,butthetimingofthishasyettobeestablishedfollowingvaccination.
Giventhepressingclinicalneedandearlysparsityofvaccinedoses,theinitialdecisionwastakentovaccinateatanintervalof12weeksfortwo-dosevaccines.Thishelpedusprotectthemostvulnerablefaster,despitesomevaccinesbeingtestedonlyateight-weekintervalsinclinicaltrials.Thelatestadviceistobringforwardthesecondjabappointmentstoeightweeks,tohelpkeepussafefromathirdwaveofinfection.
Vaccines,however,arenotmagic;theydonothingtostopusbeingexposedtoavirusifsomeonesneezesoverus,andthisiswhyrestrictionsstillplayarole.Vaccinesdohelpreducetheopportunitiesforthevirustotakeholdandtheintensityofaninfection’saftermath,whilecuttingdowntransmission.Sofar,theyareestimatedtohavesaved12,livesinEnglandalone,andpreventedmorethan30,hospitalisations.Mostvaccinatedpeoplewillshowmildsymptomsornoneatallwheninfected.Butsymptomsmayalsodependonthevariant.
Thereisstillachancethatvaccinatedpeoplewillpasstheviruson,particularlyatsuper-spreadereventsandwithhighlytransmissiblevariants,suchastheDeltavariantnowpredominantintheUK.Asnewvariantsthatcarrymutatedspikeproteinsemerge,theeffectofourcurrentjabsmaybereducedandthevaccineswillrequireupdating.Butrightnow,thereisevidencethatourvaccinesareprotectiveagainsttheDeltavariant.
Sowhatdoesasafelevelofvaccinationlooklike,inordertoprotectthoseunabletohaveajabandachieveherdimmunity?Itdependsonthevirus,andthiscoronavirushasafewtricksupitssleeve.Atthebeginningofthepandemic,expertsestimatedthatabout70%ofthepopulationneededtobevaccinatedtokeepeveryonesafefromseveredisease,buttheDeltavariantismoretransmissiblethantheoriginalvirus,andthenewestimateiscloserto85%.
Weareontherighttrack,withcautiousrestrictionsandextendingthevaccinerollout,andup
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