The vaccine coverage provides information on the efficiency of the vaccination system and the trust of the vaccination practice. Currently, Europe faces many challenges, including the spreading antivaccination sentiment . In many countries, there are people refusing vaccinations for themselves and their children, and promoting the idea that immunization is a way to do business. Moreover, there are also other reasons why vaccination practises are not shared by everyone [2,3,4]. For example, from 2016 onwards, in the USA and Europe, many antivaccination movements were pushed by the “Vaxxed: From Cover-Up to Catastrophe”. The latter is an American pseudoscience documentary film directed by Andrew Jeremy Wakefield, who was a British medical supporting the causal relationship between the trivalent MPR vaccine (measles, mumps, rubella) and the appearance of autism and intestinal disease. This theory stimulated people to lose their belief in vaccines, and thus it contributed to lead to the so-called “vaccine hesitancy phenomenon” causing a vaccination coverage reduction. The vaccines hesitancy has created health alarmism by pushing countries and international organizations, such as the World Health Organization [5, 6], to look for a way to contain this phenomenon and promote the safety of vaccines. Among the countries of the European Union, in Italy, from 2013 onwards, vaccination coverage has been showing a decreasing trend. Therefore, in 2017, a measles epidemic caused 5000 cases and four deaths . For this reason, on the 7th of June 2017, the Italian Institutions approved the Lorenzin’ decree-law, which increased the number of compulsory vaccinations from four to ten . However, this legislative manoeuvre obtained dissent from a slice of the population divided into two sides: the anti-vaccine people (encompassing who supports freedom of choice in vaccination and thus promotes the non-compulsoriness of vaccinations) and pro-vaccination people who are active in promoting positive campaigns. Both anti-vaccine and pro-vaccine people use the web to share their opinions. Today, many people find information on the World Wide Web (WWW); indeed, recent studies showed that more than half of the population has access to the Internet, and most web users seek health information there (e.g [9, 10]). Moreover, health information is more and more available on the Internet [11, 12]. There are many professional health web sites, app or social network groups to support and inform population but sometimes the quality of health information on the WWW could be a real danger for people [13, 14]. Social networks permit individuals to quickly create, share, and retrieve information, and allow anyone to give opinions and spread their message (also to anti-vaccination activists). Social networks thus contribute to false myths and misinformation about vaccines with a consequent negative impact on people’s willingness to be vaccinated [4, 15].
The aim of the paper is to analyze the online sentiment to understand if the Italian legislative intervention on vaccination is shared by the population and which are the arguments connected with this topic when people share information on YouTube. Indeed, because monitoring social networks could be a good proxy to evaluate vaccine hesitancy, understanding people thinking can guide policy-makers to plan effective information campaigns able to change people mindset regarding vaccinations.
Specifically, we focused on Italy because “Among the European countries, Italy has one of the highest levels of scepticism related to effectiveness and safety of vaccines” [16,17,18]. Moreover, to solve this problem, the Italian Institutions approved the Lorenzin’ decree-law, and thus we are also interested in understanding the effects of this manoeuvre on the sentiment of the population.
According to the “We are Social - Digital in 2018 Report”, the internet users in the world exceed four billion, and in Italy, they are more than 43 million; this means that today, more than half of the world’s population is online. In the world, Facebook has much greater penetration than YouTube  whereas, in Italy, YouTube dominates the video-based social media platforms. It was on YouTube that the North American anti-vaccine movement was able to upload and share conference recordings free of charge to a wider audience. Compared to the past, when tapes of proceeding had to be ordered by mail, YouTube allowed autism awareness groups to host instant discussions, comments, and information-sharing easily [20,21,22,23,24].
The main contribution of this research to the existing literature on the problem of vaccination hesitancy is to propose the use of text mining and sentiment analysis. Indeed, to educate people increasingly inclined to use WWW as a source of information and to understand their mindset, policy-maker need appropriate tools capable of dealing with the new digital age. Effectively, these instruments could be adopted by public authorities to understand what people’s concerns are about health, what opinion the population has regarding the health policies implemented by the institutions, and finally to know if the policies and campaigns implemented have had the expected results.
This research uses a networked mindset to tackle vaccine hesitancy. Specifically, we aim to understand what the sentiment towards vaccines on YouTube is, and finally to detect if and how the Italians’ opinion has changed from the period before the introduction of the decree-law to the following period, i.e. after the vaccination campaign.