Tuesday, October 20, 2015: 2:30 PM
Grand Ballroom A (Hyatt Regency St. Louis at the Arch)

Laura D. Scherer, PhD1, Victoria A. Shaffer, PhD1, Niraj Patel2 and Brian J. Zikmund-Fisher, PhD3, (1)University of Missouri, Columbia, MO, (2)Columbia, MO, (3)University of Michigan, Ann Arbor, MI
Purpose: One contributing factor to vaccine hesitancy is that people lack trust in claims that vaccines are safe. For example, a person who is wary of vaccines might wonder why there is a Vaccines Adverse Event Reporting System (VAERS) if vaccines are benign. The answer of course is that vaccines are (comparatively) safe because there are extremely few adverse events relative to the number of vaccine doses, and causality is often unclear in the reports that do exist. Our purpose was to determine whether expansive disclosure of VAERS information might increase trust in vaccine safety by showing individuals that adverse events are extremely rare and causality may be questioned in many of the reported events. 

Method: We recruited 1230 participants (mean age=34, SD=11; range=18-71, 83% white) to complete an online survey. Participants were randomly assigned to either (1) read the Gardasil Vaccine Information Statement from the Centers for Disease Control, (2) additionally learn how many deaths and disabilities were reported for Gardasil in 2013 (31 events total), or (3) view all of the above information and additionally read the 31 VAERS event reports. Participants who read these reports rated whether they thought that the vaccine caused these events. Afterward, participants reported their willingness to vaccinate a child (1-6 Likert scale) and their belief that the CDC is faithfully reporting vaccine risks (0-100 slider scale).

Result: Expansive disclosure of the VAERS reports caused participants to be significantly less willing to vaccinate a child (M=3.93, SD=1.84) compared to both the summary data (M=4.67, SD=1.64) and the CDC information statement (M=4.41, SD=1.76), p<.001. Participants in the expansive disclosure condition were also less likely to believe that the CDC is faithfully reporting the risks (M= 4.53, SD=1.51) compared to the other conditions (Ms=4.71, 4.85, SDs=1.36, 1.33), p=.004. Participants with preexisting negative vaccine attitudes were more likely to believe that the vaccine caused the health events reported in VAERS, r=-.39, p<.001.

Conclusion: Contrary to predictions, expansive disclosure of the VAERS reports decreased evaluations of HPV vaccine safety and reduced trust. By contrast, the VAERS summary data did not negatively affect judgments. One possible reason for these findings is that when participants read the VAERS reports, their preexisting vaccine attitudes shaped their interpretation of whether the vaccine caused each event.