The effects of immunisation upon the natural history of pertussis. A family study in the Cardiff area.

During an outbreak of pertussis in the Cardiff area in 1974, 229 children with the disease were studied to assess the effect of immunisation upon its natural history and severity. The typical clinical features of pertussis, such as paroxysmal cough, whooping, vomiting, cyanosis, and irregular breathing, were less prevalent in both the immunised and the older children. Immunisation is the main factor in protecting against complications such as fits; and, together with older age, it protects against hospitalisation. Nevertheless, pertussis today can be just as severe as it was 40 years ago, and the vaccine remains the major factor ameliorating its natural history. The immunisation programme needs more active support by all child health workers.