Background. In Italy, in recent years, vaccination coverage for key immunizations as MMR has been declining to worryingly low levels. In 2017, the Italian Govt expanded the number of mandatory immunizations introducing penalties to unvaccinated childrens families. During the 2018 general elections campaign, immunization policy entered the political debate with the Govt in charge blaming oppositions for fuelling vaccine scepticism. A new Govt established in 2018 temporarily relaxed penalties. Objectives and Methods. Using a sentiment analysis on tweets posted in Italian during 2018, we aimed to: (i) characterize the temporal flow of vaccines communication on Twitter (ii) evaluate the polarity of vaccination opinions and usefulness of Twitter data to estimate vaccination parameters, and (iii) investigate whether the contrasting announcements at the highest political level might have originated disorientation amongst the Italian public. Results. Vaccine-relevant tweeters interactions peaked in response to main political events. Out of retained tweets, 70.0% resulted favourable to vaccination, 16.5% unfavourable, and 13.6% undecided, respectively. The smoothed time series of polarity proportions exhibit frequent large changes in the favourable proportion, enhanced by an up and down trend synchronized with the switch between govt suggesting evidence of disorientation among the public. Conclusion. The reported evidence of disorientation documents that critical immunization topics, should never be used for political consensus. This is especially true given the increasing role of online social media as information source, which might yield to social pressures eventually harmful for vaccine uptake, and is worsened by the lack of institutional presence on Twitter, calling for efforts to contrast misinformation and the ensuing spread of hesitancy.
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