INVASIVE HAEMOPHILUS-INFLUENZAE DISEASE AND EPIGLOTTITIS AMONG SWISS CHILDREN FROM 1980 TO 1993 - EVIDENCE FOR HERD-IMMUNITY AMONG OLDER AGE-GROUPS

We analysed time trends in the incidence of invasive Haemophilus influ enzae disease in Switzerland between 1980 and 1993 to investigate whet her conjugated H. influenzae type b vaccines, licensed in Switzerland in May 1990, confer indirect protection to children in older, non-vacc inated age groups. Data were obtained from the records of 39 Swiss pae diatric clinics for 2,857 children 0-16 years old with invasive H. inf luenzae disease. Incidence time trends a ere analysed by Poisson regre ssion. The disease incidence decreased by 80% among 0-4-year-old child ren (i.e. those eligible for vaccination) between 1990 and 1993. Among children aged 5-16 years, there also mas an abrupt 50% fall in the in cidence of H. influenzae meningitis after 1990. However, the incidence of epiglottitis in this age group had started to decline before conju gated vaccines became available, with no additional decline thereafter . While our results suggest some indirect protection conferred to olde r, non-vaccinated children through the administration of conjugated va ccines to younger children, they also argue that underlying time trend s of invasive H. influenzae disease need not be considered when interp reting incidence rates in the vaccine era.