INTRODUCTION

Infectious diseases account for approximately 25% of global mortality, and kill at least 15 million people per year. Of those who die at least five million are children younger than 5 years of age. The burden of infectious diseases can be greatly reduced if we vaccinate all populations at high risk of disease and ensure that all children have access to basic vaccines regardless of their geographical location or economic status.

Immunisation or vaccination is the most cost-effective form of public health intervention in the protection of children, families and communities against infectious diseases. Worldwide immunisation, as well as improvements in hygiene and sanitation, have revolutionised child health and improved the quality of life of adults. Immunisation prevents millions of deaths every year, and reduces the risk of disability caused by infectious disease. In spite of these successes, however, almost two million children die every year from diseases against which effective vaccines are available at low cost.

By immunising specific population groups, for example children, serious infectious diseases and their complications can be prevented, contained and eliminated, a process referred to as herd immunity. The art of vaccination involves the production of antigenic preparations from the pathogen that are safe to administer, induce the right sort of immunity for prevention or treatment of disease, and are affordable to the population at which they are aimed.

This chapter describes the currently avail - able categories of vaccines. All health professionals have a duty to be properly trained in all aspects of immunisations and a responsibility to fully support the national childhood immunisation programmes based on the available scientific evidence.

VACCINES: A HISTORICAL PERSPECTIVE

Smallpox is a highly infectious, devastating and disfiguring disease that is caused by variola or smallpox virus, a member of the Orthopoxviridae. The disease is characterised by the presence of numerous pustules all over the body which contain infectious virus. The fatality rate is over 25% for patients infected by Variola major, while smallpox caused by V. minor has a much lower fatality rate (less than 5%).