Infant immunization with acellular pertussis vaccines in the United States: Assessment of the first two years' data from the Vaccine Adverse Event Reporting System (VAERS)

Objective. To evaluate the safety of infant immunization with acellular per tussis vaccines in the United States. Background. The US Food and Drug Administration approved the first acellula r pertussis vaccine for use in infants in the United States on July 31, 199 6. Outcome Measures. Adverse events in the United States after infant immuniza tion with pertussis-containing vaccines, representing temporal (but not nec essarily causal) associations between vaccinations and adverse events. Data Source. Reports to the Vaccine Adverse Event Reporting System (VAERS), a passive national surveillance system. Design. Reports concerning infant immunization against pertussis between Ja nuary 1, 1995 (when whole-cell vaccine was in exclusive use) and June 30, 1 998 (when acellular vaccine was in predominant use) were analyzed, if the r eports were entered into the VAERS database by November 30, 1998. Results. During the study, there were 285 reports involving death, 971 nonf atal serious reports, and 4514 less serious reports after immunization with any pertussis-containing vaccine. For 1995 there were 2071 reports; in 199 6 there were 1894 reports; in 1997 there were 1314 reports, and in the firs t half of 1998 there were 491 reports. Diphtheria-tetanus-pertussis vaccine (DTP) was cited in 1939 reports, diphtheria-tetanus-whole-cell pertussis-H aemophilus influenzae type b vaccine (DTPH) in 2918 reports, and diphtheria -tetanus-acellular pertussis vaccine (DTaP) in 913 reports. The annual numb er of deaths during the study was 85 in 1995, 82 in 1996, 77 in 1997, and 4 1 in the first half of 1998. The annual number of reported events categoriz ed as nonfatal serious (defined as events involving initial hospitalization , prolongation of hospitalization, life-threatening illness, or permanent d isability) to VAERS for all pertussis-containing vaccines declined: 334 in 1995, 311 in 1996, 233 in 1997, and 93 in the first half of 1998. Similarly , the annual number of less serious reports to VAERS for pertussis-containi ng vaccines declined: 1652 in 1995, 1501 in 1996, 1004 in 1997, and 357 in the first half of 1998. A comparison of the adverse event profiles (proport ional distributions) for DTaP, DTP, and DTPH, as well as an analysis of spe cific adverse events considered in a 1991 Institute of Medicine report on t he safety of diphtheria-tetanus-pertussis vaccine, did not identify any new , clear safety concerns. Conclusions. These findings reflect the administration of millions of doses of acellular pertussis vaccine and are reassuring with regard to the safet y of marketed acellular pertussis vaccines. VAERS data, although subject to the limitations of passive surveillance, support the prelicensure data wit h regard to the safety of the US-licensed acellular pertussis vaccines that we evaluated.