Vaccines have historically been considered to be the most cost-effective method for preventing communicable diseases. It was a vaccine that enabled global eradication of the dreaded disease smallpox. Mass immunization of children forms the anchor of the strategy of the World Health Organization (WHO) to attain "health for all" status by the year 2000. Vaccinology is undergoing a dimensional change with the advances that have taken place in immunology and genetic engineering. Vaccines that confer short or inadequate immunity or that have side effects are being replaced by better vaccines. New...