Unintentional Injury Following Vaccination — a Hypothesis Generating Study Using the Vaccine Adverse Event Reporting System (VAERS)

Background:
Injuries are a leading cause of morbidity and mortality in the United States. Unintentional injuries have been reported after vaccination, and have been identified as a vaccine safety research priority by the National Vaccine Advisory Committee.

Objectives:
To identify vaccines that might be associated with an increased risk of unintentional injuries after vaccination.

Methods:
We searched the Vaccine Adverse Event Reporting System (VAERS) database for U.S. reports received from January 1, 1998 through December 31, 2007. An injury report was defined as one involving persons aged ≥17 years whose symptoms were coded with Medical Dictionary for Regulatory Activities (MedDRA®) preferred terms containing ‘INJURY,' ‘FALL,' or ‘ROAD TRAFFIC ACCIDENT'; all identified incidents were assumed to be unintentional. We calculated the proportional reporting ratio (PRR) by comparing the proportions of injury reports for a particular vaccine with all other vaccines. The published criteria of number of cases (n) ≥3, PRR ≥2, and chi-square ≥4, were used to detect disproportionate reporting of injuries for that particular vaccine.

Results:
A total of 456 injury reports (female=60%, median age=41 years [range=17–93 years], median onset interval=0 day) involving 33 vaccines or vaccine combinations were identified; 16% of these reports included codes associated with postvaccination syncope. Injuries associated with inactivated influenza vaccine (n=110 [24%]), tetanus and diphtheria toxoids (Td) (n=76 [17%]), and quadrivalent human papillomavirus vaccine (HPV4) (n=67 [15%]) were most frequently reported. Disproportionate reporting of injury was observed for HPV4 (n=67, PRR=4.0), tetravalent meningococcal conjugate vaccine (n=22, PRR=2.9), tetanus toxoid (TT) (n=18, PRR=2.2), and rabies virus vaccine (n=17, PRR=2.1), compared with all other vaccines.

Conclusions:
VAERS data cannot be used to assess the causality of adverse events. An epidemiologic study to evaluate the type of unintentional injury outcomes and their potential association with selected vaccines will be relevant to the design of preventive interventions.