  Background. In Italy, in recent years, vaccination coverage for key
immunizations as MMR has been declining to worryingly low levels. In 2017, the
Italian Gov't expanded the number of mandatory immunizations introducing
penalties to unvaccinated children's families. During the 2018 general
elections campaign, immunization policy entered the political debate with the
Gov't in charge blaming oppositions for fuelling vaccine scepticism. A new
Gov't 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 gov't
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.
