U.S. Postlicensure safety surveillance for adolescent and adult tetanus, diphtheria and acellular pertussis vaccines: 2005-2007.

BACKGROUND

Pre-licensure clinical trials for two U.S. licensed tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccines did not reveal any major safety concerns. However, routine use in large adolescent and adult populations could reveal rare and potentially serious adverse events (AEs).

METHODS

To characterize reported AEs following Tdap vaccination and identify potential safety concerns warranting further evaluation, we analyzed data from the Vaccine Adverse Event Reporting System (VAERS) and assessed the frequency and proportions of AEs and reporting rates (reports per 100,000 vaccine doses distributed).

RESULTS

A total of 2090 reports (7% were serious; 55% listed Tdap alone) involving Tdap vaccines were submitted to VAERS May 2005-June 2007. The crude reporting rate was 10.2 per 100,000 vaccine doses distributed. The median age of vaccinees was 22 years, and the female to male ratio was about 2 to 1. The majority of reports described common local and systemic signs and symptoms, such as injection site reactions, fever, and headache. Rarely reported AEs included myopericarditis, demyelinating diseases of the central nervous system, Guillain-Barré Syndrome, syncope, encephalopathy/encephalitis, seizure, Bell's palsy, anaphylaxis, and thrombocytopenia.

CONCLUSIONS

Because adolescents and adults were not routinely vaccinated against pertussis in the past, this surveillance summary provides important - and reassuring - information about the use of Tdap in these age groups. Although subject to the limitations of passive surveillance, the findings of this VAERS review support the pre-licensure clinical trial data with regard to the safety of the U.S. licensed Tdap vaccines. Continued monitoring of clinically significant AEs that are temporally associated with Tdap vaccination and further assessment of such events using controlled observational studies may provide additional information about the safety of these vaccines.