Vaccination with Haemophilus influenzae type b meningococcal protein conjugate vaccine reduces oropharyngeal carriage of Haemophilus influenzae type b among American Indian children.

The effect of Haemophilus influenzae type b (Hib) meningococcal protein conjugate vaccine (Hib-OMPC; Merck, Sharp & Dohme) on oropharyngeal (OP) carriage of Hib was evaluated in Navajo and Apache Indian children, who are known to be at high risk for invasive Hib disease. We obtained 1423 OP swabs at well child visits from 1321 children 3 months to 4 years of age: 293 of the swabs were obtained from children before the administration of any Hib-OMPC; 1119 were taken after the primary vaccination series; and 11 after the booster dose. Swabs were tested for the presence of Hib capsular polysaccharide antigen by enzyme-linked immunosorbent assay. Forty of 1423 swabs were positive for Hib. Among the 40 positive swabs 5 (13%) were obtained from children who had received Hib-OMPC vaccine appropriate for age at swabbing, compared with 500 of 1383 (36%) of negative swabs. Children who were OP carriers of Hib were older than noncarriers (mean age, 13 and 9 months, respectively) and a greater proportion of carriers (48%) had symptoms of respiratory infection at the time of swabbing than noncarriers (30%). These variables were significantly related to increased risk of OP carriage of Hib when incorporated jointly in a logistic regression model: not vaccinated according to age (odds ratio 2.7, 95% confidence interval 1.00 to 7.05); increase of age in months (odds ratio 1.1, 95% confidence interval 1.02-1.10); and respiratory infection symptoms present (odds ratio 2.0, 95% confidence interval 1.06-3.77). Thus besides preventing invasive Hib disease, appropriate vaccination with Hib-OMPC appears to reduce OP carriage of Hib.