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 protei n conjugate vaccine (Hib-OMPC; Merck, Sharp & Dohme) on oropharyngeal (OP) carriage of Hib was evaluated in Navajo and Apache Indian childre n, who are known to be at high risk for invasive Hib disease. We obtai ned 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 th e administration of any Hib-OMPC; 1119 were taken after the primary va ccination 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 rece ived Hib-OMPC vaccine appropriate for age at swabbing, compared with 5 00 of 1383 (36%) of negative swabs. Children who were OP carriers of H ib were older than noncarriers (mean age, 13 and 9 months, respectivel y) and a greater proportion of carriers (48%) had symptoms of respirat ory infection at the time of swabbing than noncarriers (30%). These va riables were significantly related to increased risk of OP carriage of Hib when incorporated jointly in a logistic regression model: not vac cinated 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 i nterval 1.02-1.10); and respiratory infection symptoms present (odds r atio 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.