title: Association Between Vaccine Refusal and Vaccine-Preventable Diseases in the United States: A Review of Measles and Pertussis.
abstract: OBJECTIVE
  Parents hesitant to vaccinate their children may delay routine immunizations or seek exemptions from state vaccine mandates. Recent outbreaks of vaccine-preventable diseases in the United States have drawn attention to this phenomenon. Improved understanding of the association between vaccine refusal and the epidemiology of these diseases is needed.
  
  
  OBJECTIVE
  To review the published literature to evaluate the association between vaccine delay, refusal, or exemption and the epidemiology of measles and pertussis, 2 vaccine-preventable diseases with recent US outbreaks.
  
  
  METHODS
  Search of PubMed through November 30, 2015, for reports of US measles outbreaks that have occurred since measles was declared eliminated in the United States (after January 1, 2000), endemic and epidemic pertussis since the lowest point in US pertussis incidence (after January 1, 1977), and for studies that assessed disease risk in the context of vaccine delay or exemption.
  
  
  RESULTS
  We identified 18 published measles studies (9 annual summaries and 9 outbreak reports), which described 1416 measles cases (individual age range, 2 weeks-84 years; 178 cases younger than 12 months) and more than half (56.8%) had no history of measles vaccination. Of the 970 measles cases with detailed vaccination data, 574 cases were unvaccinated despite being vaccine eligible and 405 (70.6%) of these had nonmedical exemptions (eg, exemptions for religious or philosophical reasons, as opposed to medical contraindications; 41.8% of total). Among 32 reports of pertussis outbreaks, which included 10,609 individuals for whom vaccination status was reported (age range, 10 days-87 years), the 5 largest statewide epidemics had substantial proportions (range, 24%-45%) of unvaccinated or undervaccinated individuals. However, several pertussis outbreaks also occurred in highly vaccinated populations, indicating waning immunity. Nine reports (describing 12 outbreaks) provided detailed vaccination data on unimmunized cases; among 8 of these outbreaks from 59% through 93% of unvaccinated individuals were intentionally unvaccinated.
  
  
  CONCLUSIONS
  A substantial proportion of the US measles cases in the era after elimination were intentionally unvaccinated. The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals. Although pertussis resurgence has been attributed to waning immunity and other factors, vaccine refusal was still associated with an increased risk for pertussis in some populations.
authors.affiliation: Division of Infectious Diseases, Emory University, Atlanta, Georgia.
authors.forename: Varun K
authors.initials: VK
authors.lastname: Phadke
authors.affiliation: Department of Epidemiology, Emory University, Atlanta, Georgia3Emory Vaccine Center, Emory University, Atlanta, Georgia.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Bednarczyk
authors.affiliation: Institute for Vaccine Safety, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Salmon
authors.affiliation: Department of Epidemiology, Emory University, Atlanta, Georgia3Emory Vaccine Center, Emory University, Atlanta, Georgia5Department of Pediatrics, School of Medicine, Emory University, Atlanta, Georgia6Hubert Department of Global Health, Rollins School of.
authors.forename: Saad B
authors.initials: SB
authors.lastname: Omer
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008457:Measles / Q000453:epidemiology* / Q000517:prevention & control; D008458:Measles Vaccine / Q000008:administration & dosage; D008875:Middle Aged; D010567:Pertussis Vaccine / Q000008:administration & dosage; D016312:Treatment Refusal / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology; D014611:Vaccination; D014917:Whooping Cough / Q000453:epidemiology* / Q000517:prevention & control
chemical_list: D008458:Measles Vaccine; D010567:Pertussis Vaccine