Can the Vaccine Adverse Event Reporting System Be Used to Increase Vaccine Acceptance and Trust?

"One reason for vaccine hesitancy is lack of trust that vaccine harms are adequately documented and reported, yet few communication strategies have explicitly attempted to improve this trust."

This study tested the possibility that data from the national (United States, or US) vaccine adverse event reporting system (VAERS) can be used to increase trust that vaccine harms are adequately researched and that potential harms are disclosed to the public, and thereby improve perceptions of vaccines. Developed in 1990 by the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) and available online, anyone can report possible adverse reactions to vaccines for any reason, and VAERS reports are made available on the internet to the public. University of Missouri researchers proposed that open communication about VAERS could improve public trust that vaccines are safe, thereby increasing vaccine acceptance. However, findings from the study suggest that data and stories may not increase the public's acceptance of vaccines.

As the researchers explain, the VAERS database offers an opportunity to communicate real-world data that could demonstrate to individuals that: (i) every effort is being made to collect information about potential vaccine harms; (ii) in spite of this, very few events are reported; (iii) even these few reported events are not necessarily caused by the vaccine; and (iv) this information is available for anyone to view and evaluate. Their hypothesis was that communicating in a transparent and complete way about VAERS itself - how it works, what it is for, and what the database contains - could improve trust in the accuracy and honesty of the CDC's conclusions about vaccine safety and increase vaccine acceptance by concretely illustrating how few adverse events occur compared to the number of vaccinations given, as well as highlighting the CDC's efforts to monitor and document possible harms.

Using data on serious adverse events reported for the human papillomavirus vaccine (HPV) in VAERS in 2013, the researchers surveyed 1,259 adult participants' reactions to the VAERS reports. Participants were randomly assigned to one of three communication interventions. All participants read the standard 2-page CDC vaccine information statement (VIS) for the HPV vaccine. The first group was presented with the standard HPV VIS. The second group was given the same VIS as well as information about VAERS, which included data showing that out of approximately 10 million vaccinations, 24 individuals were reported to have been disabled and 7 were reported to possibly have died as a result of their vaccinations. The third group received this VAERS information and also read the detailed reports of each event.

Results showed that the CDC's VIS alone significantly increased perceptions of vaccine benefits and decreased perceived risks. Participants who were also educated about VAERS and given summary data about the serious adverse events displayed more trust in the CDC and greater HPV vaccine acceptance relative to the VIS alone. However, exposure to the detailed VAERS reports significantly reduced trust in the CDC and vaccine acceptance. (In the VIS-only condition, 73% of participants indicated that they would give a 12-year-old child the HPV vaccine, compared to 78% in the VAERS summary data group and 61% in the VAERS detailed reports group.) Hence, general information about the VAERS data slightly increased trust in the CDC and improved vaccine acceptance, but the specific VAERS reports negatively influenced both trust and acceptance. "When participants read the incident reports, there was a marked reduction in their willingness to vaccinate - even though most participants believed the vaccines caused few or even none of the deaths," said one of the authors, Laura Scherer. The modal response (N = 167, or 40.5%) was that none of the 7 deaths in the detailed reports were due to the vaccine, and only 2.2% of participants who read the reports (N = 9) believed that the vaccine caused all 7 deaths. Participants who had higher preexisting perceptions of vaccine risk were more likely to believe that the vaccine caused the adverse event, as were participants with lower education.

The researchers explore possible reasons for why the VAERS reports had a more negative effect on vaccine attitudes relative to the summary data alone. One possibility is that the individual reports allowed participants to "see what they want to see", interpreting the reports in a way that bolstered their preexisting beliefs. However, they say that, if this were the case, the effect of the intervention would have been moderated by preexisting vaccine beliefs. A second possibility is that the reports increased the vividness of adverse events, making participants more vaccine-averse even when they judged that the vaccine did not cause the events. Finally, the presence of medical jargon and terminology in the reports might have reduced participants' level of certainty regarding vaccine decisions, making them less accepting.

Scherer offers these concluding remarks: "Stories about vaccine harms can influence vaccine acceptance even when people don't completely believe them. This can potentially inform how people react to stories versus data about vaccine harms and provides a test of publicly available data on vaccine acceptance. It also means that the media should be very careful about propagating stories about vaccine harms when it is unclear that the vaccine was the cause."