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Experience in Finland with Haemophilus influenzae type b vaccines
Insights
Haemophilus influenzae type b (Hib) conjugate vaccines are highly effective in infants, significantly reducing invasive Hib infections. These vaccines provide lasting immunity, protecting children from serious illness.
Area of Science:
- Pediatrics
- Immunology
- Infectious Diseases
Background:
- Haemophilus influenzae type b (Hib) was a leading cause of childhood bacterial infections.
- Early Hib vaccines were effective only in older children (18-24 months).
Purpose of the Study:
- To evaluate the efficacy and immunogenicity of newer Hib conjugate vaccines in infants.
- To assess the development of long-lasting immunological memory after vaccination.
Main Methods:
- Conducted efficacy trials of polysaccharide-protein conjugate vaccines (PRP-D, HbOC, PRP-T) starting in 1983.
- Administered primary immunization series at 3, 4, and 6 months, with booster doses at 14-18 months.
- Monitored vaccine efficacy and incidence of invasive Hib infections in young children.
Main Results:
- Hib conjugate vaccines demonstrated immunogenicity in early infancy.
- A PRP-D conjugate vaccine trial showed 90% efficacy after primary immunization.
- No breakthrough infections occurred after booster doses in follow-up periods.
- Subsequent trials with PRP-D or HbOC vaccines also showed high protection levels.
- Vaccinations led to a significant decrease in invasive Hib infections in young children.
Conclusions:
- Hib conjugate vaccines are safe and effective for infant immunization.
- These vaccines induce lasting immunological memory, providing sustained protection.
- Widespread use of Hib conjugate vaccines has dramatically reduced the burden of invasive Hib disease in children.
Abstract:
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.