The Impact of the Politicization of Health on Online Misinformation and Quality Information on Vaccines

In July 2017, a law aimed at reversing the decline in vaccination cover (Law 119/2017) made child vaccination mandatory in Italy. The law sparked a heated debate which was a breeding ground for disinformation and misinformation but also set the stage for some initiatives that have tried to combat the problem. This paper analyzes the Twitter vaccine-related information environment by focusing on the information sources shared by about 500,000 tweets published within three years – 18 months before and after the promulgation of the Law 119/2017 on mandatory vaccinations – highlighting clusters of sources shared by the users and changes in problematic and quality information throughout that period. Results show that the politicization of the topic was associated with the growing spread of problematic information. They expose the vaccine-related information environment as characterized by an homophilic and polarized structure grouping together and opposing, on the one hand, anti-vaccination, blacklisted sources, alternative therapy and conspiracy websites, and on the other, scientific and health sources, revealing that despite the new initiatives aimed at increasing quality information and fighting problematic information online, there was a lack of scientific information both during and after the debate on the vaccinations law, while problematic information appears to have increased in volume over the years.