▁an ▁ad verse ▁effect ▁of ▁v acc ination . ▁The ▁initial ▁study ▁and ▁subsequent ▁studies ▁by ▁the ▁same ▁group ▁have ▁in ade qu ate ▁method ology — typ ically ▁a ▁poor ly ▁controlled ▁or ▁un control led ▁case ▁series . ▁A ▁prem ature ▁announ cement ▁is ▁made ▁about ▁the ▁alleg ed ▁ad verse ▁effect , ▁reson ating ▁with ▁individuals ▁suffering ▁from ▁the ▁condition , ▁and ▁under est im ating ▁the ▁potential ▁harm ▁of ▁for going ▁v acc ination ▁to ▁those ▁whom ▁the ▁v acc ine ▁could ▁protect . ▁Other ▁groups ▁attempt ▁to ▁rep licate ▁the ▁initial ▁study ▁but ▁fail ▁to ▁get ▁the ▁same ▁results . ▁Finally , ▁it ▁takes ▁several ▁years ▁to ▁reg ain ▁public ▁confidence ▁in ▁the ▁v acc ine . ▁Ad verse ▁effects ▁as cribed ▁to ▁v acc ines ▁typically ▁have ▁an ▁unknown ▁origin , ▁an ▁increasing ▁inc idence , ▁some ▁bi ological ▁pla us ibility , ▁occurr ences ▁close ▁to ▁the ▁time ▁of ▁v acc ination , ▁and ▁dread ed ▁out comes . ▁In ▁almost ▁all ▁cases , ▁the ▁public ▁health ▁effect ▁is ▁limited ▁by ▁cultural ▁boundaries : ▁English ▁speak ers ▁worry ▁about ▁one ▁v acc ine ▁causing ▁aut ism , ▁while ▁French ▁speak ers ▁worry ▁about ▁another ▁v acc ine ▁causing ▁multiple ▁s cl eros is , ▁and ▁Niger ians ▁worry ▁that ▁a ▁third ▁v acc ine ▁causes ▁infer til ity . ▁ ▁Aut ism ▁ ▁The ▁idea ▁of ▁a ▁link ▁between ▁v acc ines ▁and ▁aut ism ▁has ▁been ▁extens ively ▁investig ated ▁and ▁conclus ively ▁shown ▁to