New vaccines

New vaccines [I] The Expanded Pro-gramme on Immu-nization (EPI) seeks to achieve universal childhood immuniz- ation by 1990 using vaccines which have all been avail- able for many years against six well-known diseases: diphtheria, whooping cough, tetanus, measles, poliomyelitis and tuberculosis. But advances in biotechnology have revolutionised this field. With- in the next decade, at least a dozen new or improved vaccines will reach the market. And many more vaccines are on the way. For health problems of the future, immuniz- ation will provide more and more solutions, and additional diseases may share the fate of smallpox: global eradication. The systems of vaccine delivery now used by the EPI will become increasingly im- portant as these new products become available. Why are the promises so bright? Within only the past few years, scientists have learned techniques which permit them to identify with great accuracy the substances (pro- teins) which are responsible for im- munity, and to synthesise antigens which induce the body to make antibodies which protect from the disease in question. Such antigens can be produced through chemical synthesis, but may also be produced by genetic engineering which al- ters micro-organisms so that they themselves become manufacturing plants. In fact, it is possible through genetic engineering to remove the portions of an organism which are responsible for causing disease, but to leave the portions which stimu- late a protective response from the body, turning disease organisms into vaccines. One micro-organism can be made to carry antigens from a number of different micro-organ- isms, permitting a single vaccine to protect against a number of differ- ent diseases. The doors to a whole new frontier have been opened. Work is in progress on four of the · vaccines currently used in the EPI: whooping cough, measles, polio W ORLD HEALTH, Jan ./Feb. 1987 and BCG (the vaccine against tuberculosis). Whooping cough (or pertussis) vaccine, while still ten times or more safer than the dis- ease, still causes an unsatisfactory number of side-reactions. One in about every 300,000 immuniza- tions results in lasting neurological damage. New purified vaccines, de- veloped initially in Japan, promise fewer reactions. They are currently undergoing field trials in Sweden. Because of interference from antibodies transferred by the mother, measles vaccination must be delayed for at least nine months after birth. This varies from nine months in developing countries (where measles frequently strikes Advances in biotechnology have en- sured a promising future in the field of vaccines. Photo WHO/J. Schytte during the first year of life) to 12 to 15 months in industrialised coun- tries (where the disease usually strikes older children). But recent observations have suggested that one particular strain of measles vaccine (the so-called Edmonston Zagreb strain) may protect children from four to six months of age. This would be a boon to all countries, and field trials to confirm these observations are already under way. Two excellent polio vaccines are available. The one in most common use is the oral (Sabin) vaccine. An inactivated vaccine (Salk) is also highly effective. The Sabin vaccine, however, is associated with paraly- sis in about one in a million vac- cinees. In communities with low or moderate immunization coverage, the Salk vaccine may be less effec- tive in controlling polio than the Sabin vaccine, and is several times more expensive. It may very soon be possible to synthesise a new vaccine which will be devoid of paralytic side-effects. BCG has had a chequered his- tory. It was given a severe blow from a recent trial in India, where little or no protective efficacy against tuberculosis in adults could be demonstrated during the first follow-up years, although more re- cent data suggest that there may be some protective effect in the lower age group. Recent studies in child contacts and case-control studies showed that BCG immunization of newborn babies clearly protects them from meningitis (with an effi- cacy of up to 95 per cent) and from miliary (disseminated) TB, but is not equally effective in preventing other forms of the disease. Tuber- culosis had suffered from neglect from the research community but contributions made to WHO by Nor- way in the past two years have radically changed this situation. Today there is optimism that an entirely new vaccine might be developed. Meanwhile WHO and other UN agencies are fostering intensive re- search on new vaccines to guard against malaria and other tropical diseases. And although no safe and satisfactory protective vaccines at present exist against diarrhoea} dis- eases, current work suggests that several may be available in the near future. WHO is giving priority to the development of vaccines against rotaviruses and entero-toxigenic Escherichia coli, which cause nearly half of the serious acute episodes of diarrhoea in children under the age of five. WHO is also focusing on vaccines against cholera, shigellosis (dysentery) and typhoid fever -diseases which have important epidemic potentials. Vaccines against these three latter infections have been in existence for some time, but are not considered to be useful public health tools. They suf- fer from low efficacy, short dur- ation of protection, impractical ad- ministration schedules, high reac- tion rates, or a combination of these drawbacks. • 23