1098 AJ Hall and PG Smith important since it covers the period of life when the risk of carriage if infected is high. Thus, even if vaccine-induced immu- nity wanes later in life, there is good reason to suppose that carriage will have been prevented in a substantial proportion of vaccinated individuals, even without any booster vaccination. Direct evidence of the protective effect of hepatitis B vaccination against liver cancer comes from a study in Taiwan where all new- borns have been vaccinated since the mid 1980s. The rate of liver cancer among children aged 6–9 years in the vaccinated cohort was 1.3 million–1 year–1 compared to a rate of 5.2 million–1 year–1 in the preceding unvaccinated cohort (Chang et al, 1997). Whilst these data have accumulated the price of vaccine has fallen dramatically from around $40 per dose in the early 1980s to less than $1 per dose now. At this price it has been estimated that, in West Africa, the prevention of one carrier of the virus costs between $20 and $30, and the prevention of a case of primary liver cancer (which is uniformly fatal) only $130 (Hall et al, 1993). Since the target for vaccination is infants this is a once and for all lifetime cost for each individual in terms of prevention of HBV carriage and liver cancer. The corresponding cost in measles vaccination is around $40 per death prevented, and that of preventing a diarrhoeal death by improved water supply and sanitation is estimated at $1200 per death prevented. This evidence led the WHO to recommend universal hepatitis B vaccination for all countries of the world either in infancy (where childhood infection is common) or in pre-adolescence (where adolescent or adult infection is the main problem). Currently, although more than 100 countries have instituted this policy, there is a marked geographical disparity. The African continent lags far behind the rest of the world, despite the public health importance of liver cancer there, with only two countries having integrated hepatitis B vaccine into their national childhood vaccine programmes. The limited cancer registry data in sub-Saharan Africa suggests that this is the commonest cancer in men and the second commonest in women (Bah et al, 1990). It is estimated that some 10% of adult West Africans will die prematurely as a result of infection with the virus. Most causes of adult mortality have proved intractable to simple preventive interventions. Many of the potential preventive inter- ventions require difficult to implement changes in lifestyle. Given the importance of the long-term sequelae of hepatitis B in Africa and other developing regions of the world, the prevention of the hepatitis B carrier state by the introduction of hepatitis B vaccina- tion into routine universal childhood vaccination programmes is probably one of the simplest and most cost-effective means of reducing levels of adult mortality. Indeed, it is difficult to think of any other intervention which costs less than $3 per individual and which could have such a significant impact on adult mortality in developing countries. It is true that the major benefit would not be felt for several decades after such vaccination started but it would seem very short-sighted not to give this preventive measure high priority now. 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