EFFECT OF CONJUGATE PRP VACCINES ON THE I NCIDENCE OF INVASIVE INFECTIONS BY HAEMOPHILUS-INFLUENZAE TYPE-B IN CHILDREN

Prior to the introduction of conj ugate vaccines, Haemophilus influenz ae type b (Hib) was the leading cause of severe invasive infections in young children, in Switzerland as in other countries. From 1976 to 19 90, 150 children were treated for Hib meningitis at the Children's Hos pital of Lucerne, corresponding to an annual incidence of 9.2 cases pe r 100000 children aged under 15 years. In the same time period, the ca se fatality rate for meningitis was 4%. 87.3% of the meningitis cases occurred among children aged under 5 years. For this age group an annu al incidence of 26.4 cases per 100000 children was calculated. From 19 79 to 1990, 141 children were hospitalized for epiglottitis, correspon ding to an annual incidence of 10.9 cases per 100000 children aged und er 15. The introduction of conjugated vaccines resulted in a significa nt reduction in the frequency of invasive Hib disease. From 1991 to 19 92, 9 cases each of meningitis and epiglottitis were observed. In 1993 , only one case of meningitis and 2 cases of epiglottitis were seen. F or children under 15 years these 21 cases represent annual incidences of 3.2 cases of meningitis and 3.6 cases of epiglottitis per 100000 ch ildren. 2 of 10 meningitis cases occurred in twice vaccinated children under 2 years of age with no signs of immunodeficiency, and another c ase was seen in a 5-month-old infant vaccinated with only one dose. As suming a vaccination coverage of 70% among children under 5 during the years 1991 and 1992, the calculated efficacy is 80 to 85% for the vac cine PRP-D in this predominantly affected age group during the period when only this vaccine was available. Because of improved immunogenici ty of the newer conjugate vaccines (PRP-OMP, HB-OC, PRP-T), which make s vaccination possible from the age of 2 months on, the use of one of these new vaccines is justified. Routine vaccination with a conjugate Hib vaccine is not only recommended for all infants and children up to 5 years, but also for children who have recovered from invasive Hib i nfection or who have from immunodeficient conditions (malignancies, sp lenectomy).