Perspective: a five-country analysis of the impact of four different Haemophilus influenzae type b conjugates and vaccination strategies in Scandinavia.

Prior to vaccinations against invasive Haemophilus influenzae type b (Hib) diseases in Scandinavia, first initiated in Finland in 1986, the incidence of cases in those five countries was 49/100,000/year in 0- to 4-year-olds and 3.5/100,000 overall. During the following decade, Hib conjugates administered to young children had approximately 95% effectiveness, regardless of which conjugate was used, whether two or three primary doses were administered, and at what age in early infancy the first vaccination was given. The herd immunity effect has extended protection to older age groups. A similar effectiveness of different conjugates in five countries despite considerable diversity in approach suggests that the same impact would occur in other regions with comparable epidemiology. The Scandinavian experience supports the view that three primary vaccine doses are not imperative, thus suggesting that reducing doses of costly Hib vaccines would be one way to facilitate their usage in regions with limited resources.