Epidemiology and Infection

Indirect protection obtained by Haemophilus influenzae type b vaccination: analysis in a structured population model

T. LEINO a1c1, T. TAKALA a2, K. AURANEN a1a3, P. H. MÄKELÄ a1 and A. K. TAKALA a1a4
a1 National Public Health Institute, Helsinki, Finland
a2 Helsinki University of Technology, Espoo, Finland
a3 Rolf Nevanlinna Institute, University of Helsinki, Finland
a4 Orion Corporation, Orion Pharma, Espoo, Finland

Article author query
leino t   [PubMed][Google Scholar] 
takala t   [PubMed][Google Scholar] 
auranen k   [PubMed][Google Scholar] 
makela ph   [PubMed][Google Scholar] 
takala ak   [PubMed][Google Scholar] 


We used a structured population model to study factors determining the magnitude of indirect protection in Haemophilus influenzae type b (Hib) vaccination. On a simulation platform mimicking the population of Finland, a Hib transmission and immunity model, including cross-reactive bacterial encounters, was formulated. Utilizing different vaccination coverages and vaccine types we could study how fast the incidence of Hib disease declined due to direct and indirect vaccination effects. With the Finnish vaccination schedule we could reproduce the observed disappearance of Hib cases. Our results show that an indirect effect was already significant with a relatively low vaccine coverage, even with a vaccine only partly reducing carriage acquisition. This suggests that the vaccination schedule and vaccine to be used should be chosen to result, in addition to immunological memory, in high antibody concentrations, sufficient to reduce carriage, the latter being the main factor behind successful elimination of transmission and disease.

(Accepted March 15 2004)

c1 Dr T. Leino, National Public Health Institute, Mannerheimintie 166, FIN 00300 Helsinki, Finland.