Naturally Acquired and Conjugate Vaccine-Induced Antibody to Haemophilus influenzae Type b (Hib) Polysaccharide in Malian Children: Serological Assessment of the Hib Immunization Program in Mali

Abstract

Abstract. Haemophilus influenzae type b (Hib) conjugate vaccine for infants (6, 10, and 14 weeks of age) was introduced into the Malian Expanded Program on Immunization in July 2005, to diminish invasive Hib disease in young children. Antibodies to Hib capsular polysaccharide (PRP) were measured in infants and toddlers from an area already served by the Hib immunization program (Bamako) and in unimmunized children of the same age in a district (Kangaba) where Hib immunization had not yet begun. Among vaccinated Bamako children 6 -23 months of age, 77-93% exhibited PRP titers 1.0 μg/mL, indicating long-term protection, versus only 10 -23% of Kangaba children of that age. High PRP antibody titers in immunized children persisted through 2 years of age. Moreover,~50% of Bamako children exhibited anti-PRP titers 5.0 μg/mL; a level that impedes Hib upper respiratory carriage, and may thereby diminish the Hib transmission to the unimmunized susceptible population (i.e., providing indirect protection).

Effect of Haemophilus influenzae type b vaccination without a booster dose on invasive H influenzae type b disease, nasopharyngeal carriage, and population immunity in Kilifi, Kenya: a 15-year regional surveillance study

“… 30 In the same setting the following year, antibody decline did not begin until after 2 years of age. 31 Our results also lend support to the previously observed findings that children in developing countries generate higher anti-PRP concentrations in response to vaccination than those in developed countries such as the UK. 32 Proposed reasons for this include higher background environmental H influenzae type b exposure in developing countries and exposure to bacterial polysaccharides that cross-react with the PRP capsular polysaccharide of H influenzae type b.…”

Study of Serologic Response Rate to Haemophilus influenzae Type B After Administration of the Third Dose of Pentavalent Vaccine in Children Aged 12 Months in Karaj City in 2016

“…For example, Mali as an underdeveloped and landlocked country in West Africa started HIB vaccination in 2005 in a stepwise manner. The antibody was higher among vaccinated children than in an unvaccinated group and its protective capability persisted through 2 years of age (15). One important marker for the detection of vaccine efficacy is a serologic study on Hib antibody in different time limits after vaccination.…”

Immunization Coverage Surveys and Linked Biomarker Serosurveys in Three Regions in Ethiopia

“…It is critical to adhere closely to the EPI schedule to maximize prevention of pertussis and invasive Hib disease, since pertussis deaths cluster in the first few months of infancy [ 33 ] and in sub-Saharan Africa Hib peaks at age 6–7 months [ 34 ]. Ordinarily age 6–8 months represents the nadir for prevalence of PRP antibody titers ≥ 1.0 mcg/ml; thus, absent pentavalent immunization, few African infants this age exhibit this biomarker [ 17 , 35 ]. Even in Hintalo Wajerate, the prevalence of protective PRP titers in infants was only 68% and was only 41% and 31% in the other woredas ( Table 1 ).…”

“…In infants age 6–8 months, a high (≥ 1.0 mcg/ml) titer of serum Hib IgG anti-PRP constitutes a biomarker that the infant received pentavalent vaccine in an age range approximating the recommended EPI schedule [ 22 ]. The anti-PRP biomarker is less useful in toddlers because by that age antibodies may also derive from natural exposure to Hib or similar bacteria [ 17 ].…”