SAFETY, IMMUNOGENICITY AND AN OPEN, RETROSPECTIVE STUDY OF EFFICACY OF A MONOCOMPONENT PERTUSSIS TOROID VACCINE IN INFANTS

One hundred forty-five infants were vaccinated with 25 mu g of pertuss is toroid (NICHD-Ptxd) at 3, 5 and 7 or at 3, 5 and 12 months of age. One month after the third vaccination all had high serum IgG and neutr alizing antibodies (antitoxin) against pertussis toxin. Vaccination at 3, 5 and 12 months resulted in higher antibody titers than vaccinatio n at 3, 5 and 7 months. Sera obtained from 109 children at 3 years of age showed a decline of antibodies, but all had detectable antibodies. Adverse reactions were confined to local redness and swelling, which exceeded 2 cm after 17% of all injections. When the children were 3 ye ars old, a comparison was made of the incidence of clinical pertussis in 142 of the 145 vaccinated children and in 284 age-matched controls living in the same areas. Information on symptoms of pertussis was obt ained from the parents during telephone interviews. None of the vaccin ated children had clinical pertussis, defined as a 6-week course of pa roxysmal cough with whooping attacks or vomiting, whereas 57 controls (20%) had experienced these symptoms. Sixteen vaccinated children were exposed to pertussis in the household. Two of them had laboratory-ver ified Bordetella pertussis infections with cough of 2 and 4 weeks, res pectively, without whooping attacks or vomiting, whereas 14 did not de velop a cough. The study shows that NICHD-Ptxd is immunogenic in infan ts and that it most likely confers a high degree of protection against pertussis.