Natural Haemophilus influenzae type b capsular polysaccharide antibodies in 412 infants and children from West Africa (Burkina-Faso) and France: a cross-sectional serosurvey.

Prior to possible introduction of large-scale vaccination programmes, an estimation and comparison of naturally acquired immunity against Haemophilus influenzae type b (Hib) was carried out in two populations of age-stratified infants and children (from birth to 14 years old) in Burkina-Faso (West Africa) (n = 206) and France (n = 206). Hib capsular polysaccharide antibodies were detected by an ELISA method. The difference in the percentages of minimum protective levels for the two populations were not significant (0.15 microg/ml) for newborns (0-1 month) but became significant as early as 2 to 3 months of age (p < 0.01) when lower levels were found among infants from Burkina-Faso. Subsequently, the percentages in both countries remained low until 11 months of age and showed no significant differences. For children between 12 and 35 months, the results > or = 0.15 microg/ml were significantly higher in France (p < or = 0.05). From 36 months, the percentage of minimum seropositivity increased in Burkina-Faso, so that the difference was no longer significant. In each country, the percentage of children with the minimum protective level varied significantly (p < or = 0.05) according to age (0-47 months). None of the children from Burkina-Faso or France had antibody levels > 1.0 microg/ml before one year of age. Thereafter, only 9.51% of French children in the 12- to 17-month age stratum and 19.2% over 4 years of age had antibody levels > 1.0 microg/ml. There were no non-detectable results for children over 4 years of age, and the means for natural detectable Hib CP antibodies were > 0.15 microg/ml for both populations. Hib invasive infections depend on climate, socioeconomic status and ethnic and genetic factors. In Burkina-Faso, the large number of infants and children under 4 years of age susceptible to Hib infections suggests that large scale vaccination programmes are needed soon after birth. However, it would first be necessary to evaluate such factors as the frequency of Hib diseases in this population.