Pertussis was prevalent in many parts of New Zealand in 1982 and early 1983. Details of 187 primary family cases and spread within 231 family contacts all aged 11 or under were studied. During the lifetime of these children the pertussis immunisation programme has been two injections of adsorbed triple vaccine at three and five months of age. All primary family cases were either laboratory confirmed or were contacts of a case within that family who had been laboratory confirmed. Results reveal that, whilst a significant number of children were protected by immunisation, a substantial number were not. Where infection did occur the clinical condition was likely to be less severe. However, almost all infants of six months of age or under in the study were not immunised and received no protection. Various options to vary the pertussis immunisation programme are discussed.
