Developing better paediatric vaccines: the case of pertussis vaccine.
After 2 decades of development, acellular pertussis vaccines are becoming more widely available for use. Products that contain from 1 to 5 purified antigens of Bordetella pertussis have been assessed in safety, immunogenicity and efficacy studies and are licensed in an increasing number of countries. All acellular pertussis vaccines are associated with fewer local and systemic adverse reactions than the whole-cell pertussis vaccines that have been used for the last 50 years. The acellular pertussis vaccines elicit an antibody response that is generally equivalent to that seen with the whole-cell pertussis vaccines. The acellular pertussis vaccines are effective; using a case-definition of paroxysmal cough of 21 or more days and laboratory confirmation of pertussis, protective efficacy was variable but in excess of 70% for most products. Relative efficacy of the acellular pertussis vaccines and the whole-cell pertussis vaccines was also variable, depending on the products involved and the study design. The choice of antigen content for acellular pertussis vaccines is controversial. Although there are proponents of a monocomponent pertussis toxoid vaccine, the weight of evidence suggests that multicomponent vaccines containing pertussis toxoid and filamentous haemagglutinin and pertactin are more effective than 1- or 2-component vaccines, and that the addition of fimbriae may provide additional protection against less severe disease. Acellular pertussis vaccines are all available in combination with diphtheria and tetanus toxoids; some products also contain inactivated poliovirus vaccine and Haemophilus influenzae b-conjugate vaccine or hepatitis B vaccine. Not all acellular pertussis vaccines are available in these larger combinations because of difficulties with decreased antibody response to one or more antigens in the combined product. Future directions for research into acellular pertussis vaccines include optimisation of antigen content and administration schedule, and further development of multicomponent vaccines.
Halperin
S A
SA
Departments of Paediatrics and Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada. shalperin@iwkgrace.ns.ca