. ▁V acc ines ▁pose ▁a ▁very ▁small ▁imm un olog ic ▁load ▁compared ▁to ▁the ▁path og ens ▁naturally ▁encountered ▁by ▁a ▁child ▁in ▁a ▁typical ▁year ; ▁common ▁child hood ▁conditions ▁such ▁as ▁fe vers ▁and ▁middle - ear ▁in fe ctions ▁pose ▁a ▁much ▁greater ▁challenge ▁to ▁the ▁imm une ▁system ▁than ▁v acc ines , ▁and ▁studies ▁have ▁shown ▁that ▁v acc in ations , ▁even ▁multiple ▁concurrent ▁v acc in ations , ▁do ▁not ▁weak en ▁the ▁imm une ▁system ▁or ▁comprom ise ▁overall ▁imm unity . ▁The ▁lack ▁of ▁evidence ▁supporting ▁the ▁v acc ine ▁over load ▁hypothesis , ▁combined ▁with ▁these ▁find ings ▁directly ▁contradict ing ▁it , ▁has ▁led ▁to ▁the ▁conclusion ▁that ▁currently ▁recommended ▁v acc ine ▁programs ▁do ▁not ▁" over load " ▁or ▁weak en ▁the ▁imm une ▁system . ▁ ▁Any ▁experiment ▁based ▁on ▁with hold ing ▁v acc ines ▁from ▁children ▁is ▁considered ▁un eth ical , ▁and ▁observ ational ▁studies ▁would ▁likely ▁be ▁conf ounded ▁by ▁differences ▁in ▁the ▁health ▁care - se ek ing ▁behav iors ▁of ▁under - v acc in ated ▁children . ▁Thus , ▁no ▁study ▁directly ▁comparing ▁rates ▁of ▁aut ism ▁in ▁v acc in ated ▁and ▁un v acc in ated ▁children ▁has ▁been ▁done . ▁However , ▁the ▁concept ▁of ▁v acc ine ▁over load ▁is ▁bi olog ically ▁imp laus ible , ▁as ▁v acc in ated ▁and ▁un v acc in ated ▁children ▁have ▁the ▁same ▁imm une ▁response ▁to