Certain limitations are apparent in the prevention and control of viral and bacterial diseases by vaccines. Some organisms either do not grow in vitro, or produce only small amounts of antigen. For example, the only source of hepatitis B antigen is human plasma from chronically infected persons. The production of inactivated vaccines against highly pathogenic agents, such as those of African haemorrhagic fevers, may be hazardous to those engaged in this work. There may be technical difficulties in detoxifying or inactivating vaccines. As knowledge of the genetic basis of attenuations is meagre, vaccine strains have to be selected on arbitrary criteria. Live vaccine strains may have the potential to revert to virulence or to lose immunogenic activity. Some viruses are associated with cellular transformation and potentially with the induction of malignancy. This is true of certain herpes viruses. Owing mainly to the complexity of the etiological agents, little progress has been achieved in the control of parasitic diseases using conventionally produced vaccines.
[Developing countries] At present, fewer than 20% of the 80 million children born annually in developing countries are being fully immunized. Morbidity and mortality from diphtheria, pertussis, tetanus, measles, poliomyelitis and tuberculosis are still very high. While the reported numbers of cases and deaths may underestimate the extent of the consequences of these six diseases, they are thought to cause some 5 million deaths among children under 5 years, while blinding, crippling, or otherwise permanently disabling an additional 5 million. As is the case with the large numbers of childhood deaths estimated to be due to, for example, diarrhoeal diseases and malaria, these deaths usually occur in the context of severe malnutrition and interacting diseases; and the figures published for individual diseases usually involve considerable overlap. The leading killers are measles, pertussis and neonatal tetanus. The first two diseases affect most unimmunized children under 5 and have case-fatality rates ranging between 1% and 10%, the higher rates being more commonly observed among younger and/or less well nourished children. Although evidence on the subject is relatively scanty, it is thought that neonatal tetanus probably affects fewer than 2% of children born to unimmunized mothers in developing countries, but 70-90% of those infected die.
Every six seconds, a child dies and another is disabled from a disease which can be immunized against. Many more suffer setbacks to normal health and growth. Immunization against the six major communicable diseases of childhood - measles, tetanus, whooping cough, diphtheria, poliomyelitis and tuberculosis - costs approximately 5 dollars per child. Most of the 5 dollars is for the delivery system - the vaccines themselves cost only 50 cents. To immunize every one of the 100 million children born each year in the developing world would therefore cost approximately $500 million a year. To compare the cost of such benefits with the cost of weapons of war has become a clichÃ© of development literature. Yet it may perhaps bear pointing out that the sum of $500 million needed to prevent the deaths of 5 million children a year and the disability and malnutrition of many millions more is equivalent to the cost of only ten of today's most advanced fighter planes.