REACTOGENICITY AND IMMUNOGENICITY OF A BOOSTER DOSE OF A COMBINED DIPHTHERIA, TETANUS, AND TRICOMPONENT ACELLULAR PERTUSSIS-VACCINE AT 14 TO 28 MONTHS OF AGE

Objectives: The primary objective was to assess the nature and inciden ce of adverse events after a fourth dose of a tricomponent acellular p ertussis-diphtheria-tetanus vaccine given in the second year of life a fter primary vaccination with the same vaccine at 3, 4, and 5 months o f age. A secondary objective was to analyze the immunogenicity of the booster vaccination. Design: Of the 5361 children enrolled (aged 14 to 28 months), adverse reactions were specifically solicited from the fi rst 1863 enrollees for the first 4 days after vaccination and then wer e unsolicited for the remainder of the 4 weeks of follow-up (group 1). In the next 3498 subjects, safety and reactogenicity were entirely un solicited for this 4-week period (group 2). Immunogenicity was analyze d by means of prebooster and postbooster serum antibody titers for all vaccine components in a random subgroup of 197 children from group 1. Results: Soliciting symptoms elicited reports of at least one symptom in 1314 of 1809 children in group 1 (72.6%), including 993 (54.9%) wi th local and 885 (48.9%) with general symptoms during the first 4 days after vaccination. When symptoms were gathered in an unsolicited fash ion, only 580 of 3498 children in group 2 (16.6%) had a reported sympt om during this time, consisting of 344 (9.8%) local and 319 (9.1%) gen eral symptoms, respectively. An unsolicited symptom, areactive edemato us swelling of the whole thigh, occurred in 62 children (1.1%), with 4 5 and 17 reports in groups 1 and 2, respectively. The vast majority of all reported symptoms were mild to moderate, and all children recover ed without sequelae. Fourteen serious adverse events were reported, bu t none was considered to be related to the vaccination. lmmunogenicity analysis showed a vaccine response to perfussis toxin in 99.5% of sub jects, to filamentous hemagglutinin in 98.5%, and to pertactin (69 kd outer membrane protein) in 99%. All subjects had postvaccination antib ody titers of 0.1 IU/ml or greater against diphtheria and tetanus toxo ids. Conclusions: A fourth dose of acellular pertussis-diphtheria-teta nus vaccine as a booster dose is safe and well tolerated, although adv erse events were higher than after primary vaccination. Soliciting adv erse events increases the reports by a factor of 4 to 20, which sugges ts that the perceived clinical relevance of these events is low. The v accine was highly immunogenic and induced a booster response.