Parental refusal of pertussis vaccination is associated with an increased risk of pertussis infection in children.
Glanz JM, McClure DL, Magid DJ, Daley MF, France EK, Salmon DA, Hambidge SJ. Parental refusal of pertussis vaccination is associated with an increased risk of pertussis infection in children. Pediatrics. 2009 Jun; 123(6):1446-51.