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.
[Industrialized countries] In 1993 it was reported that, in certain pockets of the USA, fewer than half of all pre-school children have been immunized against standard diseases (compared with more than 80% in some NM / WHO-serviced countries). Cost is part of the reason; vaccinations that were about $7 in 1982 are now more than $200. Many insurance companies, and in some states government benefits, do not cover the expense. But states that do buy and distribute vaccines do not have significantly better immunization rates. The contributory reasons are inconvenient clinic hours, a scarcity of health workers, long waiting lines and a lack of information. Insufficient immunization accounted for the USA measles epidemic of 1989-90.