INTRODUCTION

Until recently, the clinical management of viral diseases depended largely on palliative measures designed to alleviate symptoms. Infections were to be avoided if at all possible or, if they could not be avoided, they were to be endured until they naturally resolved. There is, however, a long and impressive history of protection against viral diseases. The Chinese introduced inoculation against smallpox almost a thousand years ago, and they established the principle that priming of the immune system could prevent the more serious consequences of viral infection. This principle has been extensively exploited in modern times with the introduction of effective vaccines to prevent many of the more significant human viral diseases (Hilleman, 1998; Nossal, 1998; Ruff, 1999).

The power of vaccination is most dramatically demonstrated by the fact that for the first time man has been able to intervene successfully to eradicate an infectious disease from the human population. A campaign run by the World Health Organization in the late 1960s and throughout the 1970s resulted in the global eradication of smallpox with the last human case recorded in 1978. A similar campaign is under way to attempt the eradication of poliomyelitis and has involved mass vaccination of many millions of children (Hull et al., 1997). Although the disease has now been eradicated from many parts of the world, it remains in several regions that are plagued by warfare and civil disruption, and the final goal may still be several years away.

Despite the impressive achievements of vaccination programmes, especially in the control of childhood diseases, for many viral diseases the development of vaccines has proven extremely difficult.