The impact of immigration and vaccination in reducing the incidence of hepatitis B in Catalonia (Spain)

Abstract

Background: The Hepatitis B virus (HBV) infection is a major cause of liver disease and liver cancer worldwide according to the World Health Organization. Following acute HBV infection, 1-5% of infected healthy adults and up to 90% of infected infants become chronic carriers and have an increased risk of cirrhosis and primary hepatocellular carcinoma. The aim of this study was to investigate the relationship between the reduction in acute hepatitis B incidence and the universal vaccination programme in preadolescents in Catalonia (Spain), taking population changes into account, and to construct a model to forecast the future incidence of cases that permits the best preventive strategy to be adopted.

Methods: Reported acute hepatitis B incidence in Catalonia according to age, gender, vaccination coverage, percentage of immigrants and the year of report of cases was analysed. A statistical analysis was made using three models: generalized linear models (GLM) with Poisson or negative binomial distribution and a generalized additive model (GAM).

Results: The higher the vaccination coverage, the lower the reported incidence of hepatitis B (p <0.01). In groups with vaccination coverage > 70%, the reduction in incidence was 2-fold higher than in groups with a coverage <70% (p <0.01). The increase in incidence was significantly-higher in groups with a high percentage of immigrants and more than 15% (p <0.01) in immigrant males of working age (19-49 years).

Conclusions: The results of the adjusted models in this study confirm that the global incidence of hepatitis B has declined in Catalonia after the introduction of the universal preadolescent vaccination programme, but the incidence increased in male immigrants of working age. Given the potential severity of hepatitis B for the health of individuals and for the community, universal vaccination programmes should continue and programmes in risk groups, especially immigrants, should be strengthened.

Figure 1

The number of cases of hepatitis B have been modelled as smooth functions of year of report (year), vaccination coverage (vac) and proportion of immigrants (percen), using a GAM model. Results for the gam1 model (period 1992-2007) are on the left panel and on the right panel, those for gam* model (period 2000-2007). The x axis of each plot is labelled with the covariate name and the y axis is labelled s(cov,edf) where cov is the covariate name, and edf the degrees of freedom of the smooth function. Upper and lower pointwise twice-standard-error curves are included (dashed lines).

Figure 2

Incidence rate by gender and percentage of immigrants in Catalonia. Males in blue, females in red and % immigration in green.

Figure 3

Ratio (immigrant/indigenous) of the incidence rate per 100,000 population per year and cases of hepatitis B in Catalonia 2005-2007.

Figure 4

Incidence rate in Catalonia 2005-2007 according to: age group (y axis), gender (dark orange) for females and (pale orange) for males and nationality (left panel) for indigenous subjects and (right panel) immigrants.