Parents' beliefs in misinformation about vaccines are strengthened by pro-vaccine campaigns.

The main objective of this study was to determine whether one of the most commonly employed pro-vaccination strategies based on the "myths vs. facts" format can be considered an effective tool to counter vaccines misinformation. Sixty parents were randomly presented with either a control message or a booklet confronting some common myths about vaccines with a number of facts. Beliefs in the autism/vaccines link and in vaccines side effects, along with intention to vaccinate one's child, were evaluated both immediately after the intervention and after a 7-day delay to reveal possible backfire effects. Data provided support for the existence of backfire effects associated with the use of the myths vs. facts format, with parents in this condition having stronger vaccine misconceptions over time compared with participants in the control condition. The myths vs. facts strategy proved to be ineffective. Efforts to counter vaccine misinformation should take into account the many variables that affect the parents' decision-making.