Hepatitis B in a high prevalence New Zealand population: a mathematical model applied to infection control policy.

BACKGROUND

Chronic hepatitis B (CHB) is a vaccine preventable disease of global public health importance. The prevalence of CHB in New Zealand's Tongan population is over 10%, a level consistent with endemic infection, which contrasts to the low overall New Zealand prevalence (<0.5%). Despite the introduction of infant vaccination in 1988, coverage among Tongan children is estimated to be only 53%.

AIMS

To estimate the population benefit of additional public health control measures besides 'business as usual' infant vaccination for hepatitis B in high prevalence populations.

METHODS

A mathematical model of hepatitis B virus (HBV) transmission was used to predict future CHB prevalence in the New Zealand Tongan population under different infection control strategies.

RESULTS

Prevalence of CHB is predicted to plateau at 2% in the New Zealand Tongan population if coverage remains at current levels, which are therefore insufficient to achieve long-term elimination of HBV. The critical proportion of immunisation coverage for elimination of the virus is estimated to be 73%. The effect of screening for HBV carriage and early disease management was unable to be quantified, but is likely to reduce the population burden of HBV infection and thus contribute to accelerating elimination.

CONCLUSIONS AND RECOMMENDATIONS

Mathematical models are a useful tool to forecast the future burden of CHB under a range of control strategy scenarios in high prevalence populations. Serosurveillance and targeted vaccination has similarly arrested HBV transmission in time-series prevalence studies from Taiwan and Alaska. Such a policy may demonstrate similar efficacy in New Zealand ethnic groups with endemic HBV infection.