Changes in the epidemiology of hepatitis A outbreaks 13 years after the introduction of a mass vaccination program

Hum Vaccin Immunother. 2015;11(1):192-7. doi: 10.4161/hv.35861. Epub 2014 Nov 1.


A hepatitis A+B vaccine vaccination program of 12-year-olds was introduced in Catalonia in 1998. The aim of this study was to investigate the evolution of hepatitis A outbreaks in Catalonia and estimate the preventable fraction of cases associated with outbreaks as a measure of the impact of the vaccination program. Hepatitis A outbreaks reported to the Health Department between 1991 and 2012 were analyzed. The incidence rates of outbreaks, outbreak-associated cases and hospitalizations were calculated. The preventable fraction (PF) and 95% confidence intervals (CI) were estimated for the whole study period (pre-vaccination and post-vaccination) and the post-vaccination period. One-hundred-eight (108) outbreaks (rate of 2.21 per 10(6) persons-year) were reported in the pre-vaccination period and 258 outbreaks (rate of 2.82 per 10(6) persons-year) in the post-vaccination period. The rate of cases associated with outbreaks was 1.52 per 10(5) persons-year in the pre-vaccination period and 1.28 per 10(5) persons-year in the post-vaccination period. Hospitalization rates were 0.08 and 0.75 per 10(6) persons-year, respectively. The number of person-to-person outbreaks whose index case was a school contact decreased in the post-vaccination period (aOR 2.72; 95%CI 1.35-5.48), but outbreaks whose index case was a man who has sex with men (MSM) or an immigrant increased. The PF of all outbreak-associated cases was 6.46% (95%CI 3.11-9.82) and the highest PF was in the 15-24 years age group (42.53%; 95%CI 29.30-55.75). In the 0-4 years age group, the PF was 18.35% (95%CI 9.59-27.11), suggesting a protective herd effect in unvaccinated subjects. Vaccination of immigrants traveling to endemic countries and MSM should be reinforced.

Keywords: Hepatitis A; hospitalization; incidence rate; mass immunization program; outbreak; preventable fraction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • Child
  • Child, Preschool
  • Disease Outbreaks*
  • Female
  • Hepatitis A / epidemiology*
  • Hepatitis A / prevention & control*
  • Hepatitis A Vaccines / administration & dosage*
  • Hepatitis B Vaccines / administration & dosage
  • Hospitalization / statistics & numerical data
  • Humans
  • Incidence
  • Infant
  • Male
  • Mass Vaccination / methods*
  • Middle Aged
  • Risk Factors
  • Sexual Behavior
  • Spain / epidemiology
  • Young Adult


  • Hepatitis A Vaccines
  • Hepatitis B Vaccines