Decreased point prevalence of Haemophilus influenzae type b (Hib) oropharyngeal colonization by mass immunization of Brazilian children less than 5 years old with Hib polyribosylribitol phosphate polysaccharide-tetanus toroid conjugate vaccine in combination with diphtheria-tetanus toxoids-pertussis vaccine

A protective herd effect has been described after susceptible populations o f children are vaccinated with conjugate Haemophilus influenzae type b (Hib ), Hib carriage was studied in children aged 6-24 months attending day care centers in two cities in southern Brazil (Curitiba and Porto Alegre), In C uritiba, routine immunization with Hib polyribosylribitol phosphate polysac charide-tetanus toroid conjugate vaccine (PRP-T) in combination with diphth eria-tetanus toxoids-pertussis vaccine (PRP-T/DTP) has been offered since S eptember 1996; DTP vaccine alone is routinely given in Porto Alegre, Childr en in Porto Alegre (n = 643) were 8 times less likely to have received adeq uate Hib vaccination and 4 times more likely to be Hib carriers than childr en in Curitiba (n = 647; i.e., point prevalence of oropharyngeal colonizati on, 4.8% vs. 1.2%). Point prevalence of carriage with non-type b or other n ontypeable Hi was similar in children of both cities, There was a vaccinati on effect on carriage rates in children who received a primary 3-dose serie s, independent of the booster dose, suggesting that a booster may be unnece ssary to induce population protection.