Anti-capsular polysaccharide antibody concentrations in saliva after immunization with Haemophilus influenzae type b conjugate vaccines.

IgG and IgA antibodies to Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) were measured in saliva of 7- to 19-month-old children after vaccination with 2 or 3 doses of Hib conjugate vaccine. Both the concentration and the prevalence of these antibodies were higher after 3 than after 2 doses of vaccine. The presence and concentration of IgG Hib PS antibodies in saliva correlated with their concentration in serum. Fifty-four percent (20 of 37) of the children with serum IgG concentrations higher than 30 micrograms/ml had detectable salivary IgG, whereas the 21 children with a low serum IgG concentration (< 3 micrograms/ml) had no IgG in saliva. The IgA anti-Hib PS in saliva was mainly secretory and was found in saliva of 29% (19 of 65) of the children who had no detectable serum IgA anti-Hib PS. The results suggest that the IgG anti-Hib PS in saliva was derived from serum, whereas the IgA antibodies were locally produced. The Hib PS antibodies on mucosa are suggested to be responsible for the reduction of Hib carriage observed among children vaccinated with Haemophilus type b conjugates.