▁those ▁who ▁surv ive ▁the ▁disease ▁become ▁perman ently ▁imm une . ▁As ▁discussed ▁below , ▁the ▁philosoph ies ▁of ▁some ▁alternative ▁medicine ▁pract ition ers ▁are ▁in compatible ▁with ▁the ▁idea ▁that ▁v acc ines ▁are ▁effective . ▁ ▁Population ▁health ▁ ▁In complete ▁v acc ine ▁coverage ▁increases ▁the ▁risk ▁of ▁disease ▁for ▁the ▁entire ▁population , ▁including ▁those ▁who ▁have ▁been ▁v acc in ated , ▁because ▁it ▁reduces ▁her d ▁imm unity . ▁For ▁example , ▁the ▁meas les ▁v acc ine ▁is ▁given ▁to ▁children ▁between ▁the ▁ages ▁of ▁ 9 ▁and ▁ 1 2 ▁months , ▁and ▁the ▁short ▁window ▁between ▁the ▁disapp earance ▁of ▁mat ernal ▁ant ib ody ▁( before ▁which ▁the ▁v acc ine ▁often ▁fails ▁to ▁ser o convert ) ▁and ▁natural ▁in fection ▁means ▁that ▁v acc in ated ▁children ▁are ▁frequently ▁still ▁vulner able . ▁H erd ▁imm unity ▁less ens ▁this ▁vulner ability ▁if ▁all ▁the ▁children ▁are ▁v acc in ated . ▁In cre asing ▁her d ▁imm unity ▁during ▁an ▁out break ▁or ▁risk ▁of ▁out break ▁is ▁perhaps ▁the ▁most ▁widely ▁accepted ▁just ification ▁for ▁mass ▁v acc ination . ▁When ▁a ▁new ▁v acc ine ▁is ▁introduced ▁mass ▁v acc ination ▁helps ▁increase ▁coverage ▁rapidly . ▁ ▁If ▁enough ▁of ▁a ▁population ▁is ▁v acc in ated , ▁her d ▁imm unity ▁takes ▁effect , ▁decre asing ▁risk ▁to ▁people ▁who ▁cannot ▁receive ▁v acc ines ▁because ▁they ▁are ▁too ▁young ▁or ▁old , ▁imm uno