Naturally acquired immunity to Haemophilus influenzae type B in healthy Cuban children

Abstract

We have evaluated the prevalence of antibody to immunogenicity of Haemophilus influenzae type b (Hib) Key words: Haemophilus influenzae type b -natural immunity -pre-vaccination antibody titres -CubaHaemophilus influenzae type b (Hib) disease is now a major cause of vaccine-preventable morbidity and mortality in young children in developing countries. Despite the availability of a protective vaccine, few developing countries are using Hib vaccine in their immunization programs. The major obstacle to the routine use of Hib conjugate vaccine in most non-industrialized countries is cost (Fernández et al. 2000).In Cuba the Hib vaccination was introduced in the National Immunization Program in 1999, for all the children born between January 1998 and October 1999. After that, the incidence of Hib disease has decreased to 0.1 per 100,000 inhabitants, in (Dickinson et al. 2001. The purpose of this study was to evaluate the natural acquired immunity to Hib in a group of healthy children 4 to 5 years of age in the last cohort not vaccinated against Hib.This study was performed between February and May 2002, in the province of Camagüey, Cuba. Nine hundred and seventy four healthy children attending day care centers and schools were selected. No child had previously received Hib vaccine or had received any immunoglobulin preparation or blood product. Demographic and medical data were obtained through a personal interview with the mothers. Blood samples were drawn from children, and the serum was stored at -20°C until further analysis.Serum capsular polysaccharide specific IgG antibody (anti-PRP) concentrations were measured by a modification of the enzyme-linked immunosorbent assay (ELISA) using HbOHA (NIBSC, Potters Bar, UK) as antigen. dard curve was generated by using reference serum (lot 1983 Center for Biological Evaluation and Review, Food and Drug Administration, Bethesda, MD) with a calculated IgG antibody concentration (60.9 µg/ml) (Keythy et al. 1987, Phipps et al. 1990). IgG antibody concentration was logarithmic transformed and the geometric mean concentration (GMC) was calculated.Nasopharyngeal swabs were collected and inoculated on chocolate agar medium supplemented with V and X factor, and incubated in 5% CO 2 in air at 37°C overnight. Isolates were identified as H. influenzae by their requirements for V and X factors (BBL TAXO X and V FACTOR STRIPS, Becton Dickinson Microbiology System