HEMOPHILUS-INFLUENZAE TYPE-B CAPSULAR POLYSACCHARIDE VACCINE IN CHILDREN - DOUBLE-BLIND FIELD-STUDY OF 100,000 VACCINEES 3 MONTHS TO 5 YEARS OF AGE IN FINLAND

Abstract

A recently developed H. influenzae type b capsular polysaccharide vaccine was given to 48,977 children 3 mo.-5 yr of age; an equal number of children receiving group A meningococcal vaccine served as controls. The protection as well as serum antibody response was strongly age-dependent. Among children who received the H. influenzae type b vaccine when 18 mo. of age of older, there were no cases of bacteremic disease caused by H. influenzae type b in the 1st yr after vaccination. At the same time, 11 such cases were seen in the control group of the same age, a highly significant difference. In the 2nd yr after vaccination, 2 cases occurred in the H. influenzae type b-vaccinated group, 5 in the meningococcal-group A vaccinated group. No protection was seen among children who were younger than 18 mo. when vaccinated, even if they received a booster dose of the vaccine. The serum antibody response to the H. influenzae type b polysaccharide, measured by radioimmunoassay, was poor in children below 18 mo. of age and good in those above it. No effect of the vaccine could be seen on the nasopharyngeal carriage of H. influenzae type b, which was approximately 6% in this age group. Adverse effects of the vaccine were mild.