Abstract
Haemophilus influenzae type b (Hib) is now recognized as an important pathogen in Asia. To evaluate disease susceptibility, and as a marker of Hib transmission before routine immunization was introduced in Kathmandu, 71 participants aged 7 months–77 years were recruited and 15 cord blood samples were collected for analysis of anti-polyribosylribitol phosphate antibody levels by enzyme-linked immunosorbent assay. Only 20% of children under 5 years old had levels considered protective (>0.15 µg/ml), rising to 83% of 15–54 year-olds. Prior to introduction of Hib vaccine in Kathmandu, the majority of young children were susceptible to disease.
Highlights
Haemophilus influenzae type b (Hib) remains a significant cause of invasive bacterial disease globally, and is of particular importance in resource-poor countries
In the 0.5–4 year-olds the anti-polyribosylribitol phosphate (PRP) geometric mean concentration (GMC) and percentage protected were low in relation to the pre-defined protective thresholds; of note, no children in this age-group had an anti-PRP concentration .1 mg/ml
The GMC and percentage with antibody concentrations greater than the protective thresholds were higher in 5–7 year-olds, with the majority of this age-group (60%) having antibody levels .0.15 mg/ml
Summary
Haemophilus influenzae type b (Hib) remains a significant cause of invasive bacterial disease globally, and is of particular importance in resource-poor countries. In unvaccinated populations, repeated exposure to Hib antigens during childhood is thought to lead to natural immunity, with development of protective levels of anti-PRP antibody over time [5]. The aim of this seroepidemiological study, carried out in the pre-Hib-vaccination era in Nepal, was to determine the level of Hib-specific serum antibodies in a sample of the Kathmandu population, in order to evaluate disease susceptibility, and as a surrogate marker of Hib transmission prior to vaccine introduction. In addition these data may provide a useful baseline against which to compare post-vaccination seroepidemiological studies, for example when determining whether a booster vaccine dose will be needed in this population [6]
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