EXPERIENCE IN FINLAND WITH HAEMOPHILUS-INFLUENZAE TYPE-B VACCINES

The importance of Haemophilus influenzae type b (Hib) as the leading cause of bacteraemic infections in children was recognized in the early 1970s in Finland. An efficacy trial with the capsular polysaccharide vaccine demonstrated the efficacy of this first generation vaccine, but only from ages 18-24 months onwards. For this reason, since 1983 new polysaccharide-protein conjugate vaccines (PRP-D, HbOC, and PRP-T) have been extensively tested. These studies have shown that conjugate vaccines are immunogenic in early infancy and are capable of generating a lasting immunological memory. A second Hib vaccine efficacy trial in 1986-1987 showed that the conjugate vaccine (PRP-D) was 90% efficacious after the primary immunization series at 3, 4 and 6 months. After a booster dose at 14-18 months, no failure cases have occurred during the follow-up period. The same level of protection seems to be true also in a subsequent trial, where two Hib conjugate vaccines (PRP-D or HbOC) were given at 4, 6 and 14-18 months. These vaccinations have led to a significant decline in the number of invasive Hib infections in young children.