Should adolescents be vaccinated against hepatitis A: the Hong Kong experience

Hong Kong is a well developed city in the center of an endemic region for hepatitis A. The age at which hepatitis A occurs has shifted from childhood and adolescence to adults like many western countries. There is a high chance of outbreaks with the introduction of infection from neighbouring countries. Reducing the susceptibility of a population by vaccination can eliminate the diseases but updated sero-epidemiological data is needed to analyse the level of natural immunity, and identify those susceptible to infection for preventive measures. This study conducted amongst secondary school children seeks to identify those who are at risk and to obtain data on the present sero-prevalence of anti-HAV. Overall prevalence of anti-HAV in this age group was 7% increasing with age. Analysed by multiple regression model, those students living in mainland China over 3 years had odds ratio of 31.6 (95% c. i. 17.4-57.3) compared with those born in Hong Kong. Students with a father in a skilled occupation and an education level of secondary school or above, and both parents with secondary education or above, had an odds ratio of 0.22 (95% c.i. 0.07-0.7) and 0.35 (95% c.i. 0. 17-0.72) associated with presence of anti-HAV, respectively. Improved socio-economic state exposes higher proportion of the population at risk. Immunisation is worthwhile to be considered for the adolescents in Hong Kong. Prevaccination screening is cost effective only for those adolescents who are most likely to have natural immunity.