Injection-site reactions to booster doses of acellular pertussis vaccine: rate, severity, and anticipated impact.

BACKGROUND Acellular pertussis (aP)-containing vaccines cause fewer adverse events than whole-cell versions for primary doses. Booster doses, however, may be followed by extensive injection-site reactions. This study compares the frequency, severity, and impact of local reactions among children receiving 5 consecutive doses of an aP combination vaccine (including inactivated polio virus, conjugated Haemophilus influenzae type b antigen, and diphtheria and tetanus toxoids) to children receiving a mixed series of whole-cell and aP combination vaccines. METHODS Participants were parents or guardians of children 4 to 6 years old immunized at public health clinics across British Columbia, Canada. This included 398 children receiving the fifth consecutive dose of an aP combination vaccine and 402 receiving the fifth dose in a mixed series consisting of at least 1 prior dose of whole-cell pertussis combination vaccine with the remainder as aP combination vaccine. A cross-sectional telephone survey evaluated the extent of local reactions 48 to 96 hours after immunization by asking participants to compare the size of redness and swelling with familiar household items such as Oreo cookies or coins. Associated discomfort and impact on recreational activities, health care utilization, parental time off work, and attitudes toward immunization were also assessed. RESULTS Children who received the fifth consecutive dose of an aP combination vaccine more often experienced redness (24%) or swelling (16%) the size of an Oreo cookie or larger (>or=46 mm) than children given a mixed series (10% and 9%, respectively) but less often experienced tenderness or limitation of movement at the injection site. Related health care utilization was low. There was no discernible effect on participation in recreational activities or parental attitudes toward vaccine; 90% would recommend the same vaccine to others with children of the same age. CONCLUSIONS We conclude that injection-site reactions are more extensive after the fifth consecutive dose of an aP combination vaccine compared with the fifth dose in a mixed series of whole-cell and aP combination vaccines. These reactions are unlikely to affect parental acceptance of immunization recommendations or health care utilization.