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

Abstract

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 10⁶ persons-year) were reported in the pre-vaccination period and 258 outbreaks (rate of 2.82 per 10⁶ persons-year) in the post-vaccination period. The rate of cases associated with outbreaks was 1.52 per 10⁵ persons-year in the pre-vaccination period and 1.28 per 10⁵ persons-year in the post-vaccination period. Hospitalization rates were 0.08 and 0.75 per 10⁶ 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
• outbreak
• mass immunization program
• preventable fraction
• incidence rate
• hospitalization

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgements

This work was partially funded by CIBER Epidemiología y Salud Pública (CIBERESP), Spain and by AGAUR (expedient number 2009/SGR 42).

We thank the reporting Physicians and the technicians of the Epidemiological Surveillance Units of the Public Health Agency of Catalonia and of the Epidemiology Service of the Public Health Agency of Barcelona.

The other members of the Working Group for the Study of Hepatitis A in Catalonia

M Alsedà, C Arias, I Barrabeig, N Camps, M Carol, M Company, J Ferràs, G Ferrús, I Parrón, A Rovira, R Torras (Public Health Agency of Catalonia); P Olalla, and J Caylà (Public Health Agency of Barcelona and CIBER Epidemiología y Salud Pública).