title: Smallpox vaccination and all-cause infectious disease hospitalization: a Danish register-based cohort study.
abstract: BACKGROUND
  There is growing evidence from observational studies and randomized trials in low-income countries that vaccinations have non-specific effects. Administration of live vaccines reduces overall child morbidity and mortality, presumably due to protection against non-targeted infections. In Denmark, the live vaccine against smallpox was phased out in the 1970s due to the eradication of smallpox. We used the phasing-out period to investigate the effect of smallpox vaccination on the risk of hospitalization for infections.
  
  
  METHODS
  From the Copenhagen School Health Records Register, a cohort of 4048 individuals was sampled, of whom 3559 had information about receiving or not receiving smallpox vaccination. Infectious disease hospitalizations were identified in the Danish National Patient Register.
  
  
  RESULTS
  During 87,228 person-years of follow-up, 1440 infectious disease hospitalizations occurred. Smallpox-vaccinated individuals had a reduced risk of all-cause infectious disease hospitalization compared with smallpox-unvaccinated individuals [hazard ratio (HR) 0.84; 95% confidence interval (CI) 0.72-0.98]. The reduced risk of hospitalizations was seen for most subgroups of infectious diseases. The effect may have been most pronounced after early smallpox vaccination (vaccination age <3.5 years: HR 0.81; 95% CI 0.69-0.95; vaccination age ≥ 3.5 years: HR 0.91 95% CI 0.76-1.10). Among the smallpox-vaccinated, the risk of infectious disease hospitalization increased 6% with each 1-year increase in vaccination age (HR 1.06; 95% CI 1.02-1.10).
  
  
  CONCLUSIONS
  Smallpox vaccination is associated with a reduced risk of infectious disease hospitalization in a high-income setting.
authors.affiliation: Bandim Health Project, Statens Serum Institut, Copenhagen, Denmark. sgs@ssi.dk; mvm@ssi.dk
authors.forename: Signe
authors.initials: S
authors.lastname: Sørup
authors.forename: Marie
authors.initials: M
authors.lastname: Villumsen
authors.forename: Henrik
authors.initials: H
authors.lastname: Ravn
authors.forename: Christine Stabell
authors.initials: CS
authors.lastname: Benn
authors.forename: Thorkild I A
authors.initials: TI
authors.lastname: Sørensen
authors.forename: Peter
authors.initials: P
authors.lastname: Aaby
authors.forename: Tine
authors.initials: T
authors.lastname: Jess
authors.forename: Adam
authors.initials: A
authors.lastname: Roth
mesh_terms: D000293:Adolescent; D000328:Adult; D002675:Child, Preschool; D015331:Cohort Studies; D003140:Communicable Disease Control / Q000379:methods; D003141:Communicable Diseases / Q000453:epidemiology*; D003718:Denmark / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D016016:Proportional Hazards Models; D012042:Registries; D012307:Risk Factors; D012574:Schools; D012900:Smallpox Vaccine / Q000008:administration & dosage*; D014611:Vaccination / Q000706:statistics & numerical data*; D055815:Young Adult
chemical_list: D012900:Smallpox Vaccine