. ▁ ▁There ▁was ▁legit imate ▁concern ▁from ▁supp or ters ▁of ▁v acc ination ▁about ▁its ▁safety ▁and ▁effic acy , ▁but ▁this ▁was ▁over shadow ed ▁by ▁general ▁condem n ation , ▁particularly ▁when ▁legisl ation ▁started ▁to ▁introduce ▁comp uls ory ▁v acc ination . ▁The ▁reason ▁for ▁this ▁was ▁that ▁v acc ination ▁was ▁introduced ▁before ▁labor atory ▁methods ▁were ▁developed ▁to ▁control ▁its ▁production ▁and ▁account ▁for ▁its ▁fail ures . ▁V acc ine ▁was ▁maintained ▁initially ▁through ▁arm - to - arm ▁transfer ▁and ▁later ▁through ▁production ▁on ▁the ▁skin ▁of ▁animals , ▁and ▁b acter i ological ▁ster ility ▁was ▁impossible . ▁Further , ▁identification ▁methods ▁for ▁potential ▁path og ens ▁were ▁not ▁available ▁until ▁the ▁late ▁ 1 9 th ▁to ▁early ▁ 2 0 th ▁century . ▁D ise ases ▁later ▁shown ▁to ▁be ▁caused ▁by ▁cont amin ated ▁v acc ine ▁included ▁er ys ip el as , ▁t uber cul osis , ▁t et anus , ▁and ▁sy ph ilis . ▁This ▁last , ▁though ▁rare — est im ated ▁at ▁ 7 5 0 ▁cases ▁in ▁ 1 0 0 ▁million ▁v acc in ations — att ract ed ▁particular ▁attention . ▁Much ▁later , ▁Dr . ▁Charles ▁Cre ight on , ▁a ▁leading ▁medical ▁oppon ent ▁of ▁v acc ination , ▁claimed ▁that ▁the ▁v acc ine ▁itself ▁was ▁a ▁cause ▁of ▁sy ph ilis ▁and ▁devoted ▁a ▁book ▁to ▁the ▁subject . ▁As ▁cases ▁of ▁small po x ▁started