Haemophilus influenzae Type B conjugate vaccine introduction in Mali: impact on disease burden and serologic correlate of protection

In Bamako, Mali, where surveillance revealed a high incidence of Haemophilus influenzae type b (Hib) invasive disease, Hib conjugate vaccine was introduced into the Expanded Program on Immunization and the impact assessed. Annual confirmed Hib hospitalizations for infants 0-11 months of age fell from 175/10(5) to 44/10(5) (P0.001); among infants 6-7 months of age Hib hospitalizations fell from 377/10(5) to 69/10(5), (82% decrease, P0.001). Invasive Streptococcus pneumoniae hospitalizations remained unchanged. In a baseline serosurvey, only 3/200 infants 6-7 months of age (1.5%) had protective anti-polyribosylribitol phosphate (PRP) titersor = 0.15 microg/mL and 1(0.5%) hador = 1.0 microg/mL. In serosurveys 18 and 30 months after vaccine introduction, 168/201 (84%) and 184/200 (92%) infants, respectively, had titersor = 0.15 microg/mL and 141/201 (70%) and 163/200 (82%) had titersor = 1.0 microg/mL. Introduction of Hib vaccine led to rises in anti-PRP seroprevalence, significant reductions in Hib disease, and all-cause hospitalizations, whereas S. pneumoniae disease remained unchanged.