EFFICACY OF A MONOCOMPONENT PERTUSSIS TOXOID VACCINE AFTER HOUSEHOLD EXPOSURE TO PERTUSSIS

In a double-blind, placebo-controlled efficacy trial of a monocomponen t pertussis toroid vaccine, 3450 infants were randomly assigned to vac cination with diphtheria-tetanus toxoids with or without pertussis tor oid at 3, 5, and 12 months of age. Study children and family members w ere investigated for possible pertussis with cultures, serology, and p olymerase chain reaction. Efficacy was 71% after 3 doses when the Worl d Health Organization case definition of pertussis (which includes par oxysmal cough for 21 days or longer) was used, We report the efficacy in the subgroup of children who were exposed to pertussis in the house hold, Among study children exposed to pertussis in the household from the day of the third vaccination, 20 of 99 (20%) recipients of diphthe ria-tetanus-pertussis toxoids vaccine and 64 of 79 (81%) recipients of diphtheria-tetanus toxoids vaccine had pertussis fulfilling criteria of the World Health Organization, The vaccine efficacy was 75% (95% co nfidence intervals 64% to 84%), In children who had received only two doses at the time of household exposure, vaccine efficacy was 66% (95% confidence intervals 15% to 90%) based on 4 cases among 32 household- exposed recipients of diphtheria-tetanus-pertussis toxoids vaccine and 13 cases among 35 household-exposed recipients of diphtheria-tetanus toxoids vaccine, In conclusion, the pertussis toroid vaccine provides protection against pertussis both after household and community exposu re.