Booster immunisation for diphtheria and tetanus: no evidence of need in adults.

Recommendations to give adults diphtheria and tetanus toxoid every ten years have been based on serological surveys that have shown lower antibody levels in older populations. The purpose of an immunisation programme, however, is to prevent disease and not merely to produce antibodies. In Canada, although an immunisation programme against diphtheria has been in operation for nearly sixty years, age-specific morbidity and mortality rates for diphtheria do not show an increase with age. Similarly, age-specific death rates from tetanus do not show any increase. From Canadian surveillance data, there is no evidence to suggest that people are leaving the immune pool and entering the susceptible pool. Immunisation programmes do not need to include routine administration of booster doses of diphtheria and tetanus toxoids to adults since the benefits of the procedure do not justify the risks or costs. Continuing case-surveillance will bring to light any increase in incidence of disease justifying a need for an adult programme.