. ▁▁ ▁The ▁over wh el ming ▁success ▁of ▁certain ▁v acc in ations ▁has ▁made ▁certain ▁dise ases ▁rare ▁and ▁consequ ently ▁this ▁has ▁led ▁to ▁incorrect ▁he ur istic ▁thinking ▁among ▁people ▁who ▁are ▁v acc ine - hes it ant . ▁Once ▁such ▁dise ases ▁( e . g ., ▁Ha em oph ilus ▁influen za e ▁B ) ▁decrease ▁in ▁pre val ence , ▁people ▁may ▁no ▁longer ▁appreciate ▁how ▁serious ▁the ▁ill ness ▁is ▁due ▁to ▁a ▁lack ▁of ▁familiar ity ▁with ▁it ▁and ▁become ▁compla cent . ▁The ▁lack ▁of ▁personal ▁experience ▁with ▁these ▁dise ases ▁reduces ▁the ▁perce ived ▁danger ▁and ▁thus ▁reduces ▁the ▁perce ived ▁benefit ▁of ▁imm un ization . ▁Con vers ely , ▁certain ▁ill ness es ▁( e . g ., ▁influen za ) ▁remain ▁so ▁common ▁that ▁v acc ine - hes it ant ▁people ▁mistaken ly ▁perce ive ▁the ▁ill ness ▁to ▁be ▁non - th re aten ing ▁despite ▁clear ▁evidence ▁that ▁the ▁ill ness ▁pos es ▁a ▁significant ▁threat ▁to ▁human ▁health . ▁O mission ▁and ▁dis confirm ation ▁bi ases ▁also ▁contribute ▁to ▁v acc ine ▁hes it ancy . ▁▁ ▁Vari ous ▁concerns ▁about ▁imm un ization ▁have ▁been ▁raised . ▁They ▁have ▁been ▁addressed ▁and ▁the ▁concerns ▁are ▁not ▁supported ▁by ▁evidence . ▁Conc ern s ▁about ▁imm un ization ▁safety ▁often ▁follow ▁a ▁pattern . ▁First , ▁some ▁investig ators ▁suggest ▁that ▁a ▁medical ▁condition ▁of ▁increasing ▁pre val ence ▁or ▁unknown ▁cause ▁is