SUMMARY
The communication of information about vaccines and anti-vaccines is analyzed through the monitoring of issuers, news sites, groups, and messages in social networks. We also investigate the effects of information on people’s attention, emotion, and engagement, which were analyzed using eye tracking, galvanic skin response (GSR) and facial expression methods. Results: the flow of communication was not constant, both in the press and on web sites (376 news in 2015, 74 in 2016, 69 in 2017 and, 268 in 2018); posts were informative and neutral; and 80% came from non-professional sources (only 17% were written by a journalist and 3% by a health specialist). On social networks, anti-vaccine Facebook messages and groups were identified, and a mapping of influencers is presented. Analysis of the temporal evolution (years 2015 to 2018) of communicative flows showed that anti-vaccine posts decreased. Gender differences appeared in the visual exploration of information sources and in the provoked emotion responses (GSR and facial expression). In pro-vaccine pages women looked at the headline first, while men looked at the photograph. Emotional responses and engagement did not show differences between anti-vaccine and pro-vaccine web sites. No differences were found in the emotion provoked (GSR) between both website types: anti-vaccination persuasion occurred via cognitive, not emotional, methods by using heuristics (e.g., conspiracy theories). Emotional responses and engagement did not show differences between pro-vaccine and anti-vaccine web sites.