New acellular pertussis-containing paediatric combined vaccines

Combined pediatric vaccines have the advantages of conferring protection ag ainst multiple common infectious diseases with a reduced number of injectio ns. Their use should lead to better compliance to recommended vaccination s chedules. Diphtheria (D), tetanus (T) and whole-cell pertussis vaccine (P) have been successfully combined, with or without inactivated poliovirus vac cine (IPV) in the same syringe for many years. Recently developed acellular pertussis (aP) Haemophilus influenzae type B (Hib), inactivated poliomyeli tis virus and hepatitis B vaccines are ideal candidates for inclusion in cu rrent combined vaccines. Nevertheless, the development of new combinations has to face preclinical and clinical issues: the appropriate formulation of the new antigen(s) and other vaccine components needs to be determined to ensure compatibility and guard against potential additive or unexpected adv erse reactions: potential immunological interference between antigens and t he negative impact of other vaccine components on immunogenicity may occur, and these have to be examined also. Whole-cell pertussis vaccines are high ly protective against whooping cough, but the severe adverse reactions that these vaccines sometimes produce have led to hesitation over their use, in cluding the decision of some countries to stop pertussis immunization. To i ncrease the acceptability of pertussis vaccination, Pasteur Merieux Connaug ht has developed a combined D. T and a two-component acellular pertussis va ccine (DTaP), composed of purified pertussis toroid (PT) and filamentous ha emagglutinin (FHA), which has been shown to be effective in an efficacy tri al conducted in Senegal. Acellular DTaP vaccines are immunogenic and have a better safety profile than DTP vaccines. when given either for the primary series. for the booster vaccination or for both. In order to meet worldwid e demands, the combined DTaP-IPV or DTP-IPV has been developed for countrie s where IPV is recommended. Following the encouragement of the WHO, an H. i nfluenzae type B tetanus-conjugated (Act-HIB) vaccine, has been combined in a full liquid formulation with the whole-cell D-TP. This vaccine showed a good safety and immunogenicity profile in infants and in toddlers. A combin ed DTaP-IPV-PRP-T vaccine (where the Act-HIB vaccine is reconstituted by th e full-liquid DTaP-IPV) also has been successfully developed both for the p rimary series and for booster vaccination; although, a reduced immunogenici ty against PRP observed after the primary series, this did not affect vacci ne priming. Hepatitis B immunization campaigns targeting high-risk groups h ave failed to control the disease in areas of low endemicity. In 1992, the WHO recommended that hepatitis B vaccination should be integrated into the EPI in all countries by 1997-1999. For that purpose, hepatitis B vaccine is currently evaluated in pediatric combined vaccines. Developing new combina tion vaccines is a difficult but essential process for maintaining high imm unization rates worldwide against infectious diseases, provided that the co sts are acceptable. New combined vaccines including pneumococcal and mening ococcal component are under wide-scale development. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.