The Visual Vaccine Debate on Twitter: A Social Network Analysis

People with pro- and anti-vaccination stances use social media outlets, such as Twitter, to join conversations about vaccines, disseminate information or misinformation about immunisation, and advocate in favour or against vaccinations. These users often share images to emphasise their messages and influence their audiences. This study explores how vaccine visual information (and misinformation) circulates within and among Twitter networks and identifies the various actors that could potentially influence the flow of vaccination images and, by extension, discussion and action around vaccine decision-making and uptake.

The researchers conducted a social network analysis on samples of tweets with images collected in June, September, and October 2016 - final samples of 3,573, 1,932, and 3,778 tweets in those months, respectively. They gathered only tweets written in English, having an image uploaded on Twitter originally, and featuring at least one of the following hashtags: #vaccine(s), #vaccination(s), #immunization, #vaccineswork, #whyIvax, #antivax, #CDCwhistleblower, #vaccineinjury, #vaxxed, and #hearus. They classified the tweets as follows:

• Anti-vaccine: Tweets strongly against vaccinations, claiming conspiracy theories, disseminating misinformation about vaccines, or opposing pro-vaccine messages
• Pro-vaccine: Tweets strongly in favour of vaccinations, promoting immunisation campaigns, providing medical advice regarding vaccinations, or mocking anti-vaccine claims
• Pro-safe vaccine: Tweets expressing concerns about vaccinations - e.g., the need for more controls and ethical considerations in vaccine production, administration, and business
• News: News tweets that included text, web links, hashtags, or images that referred to newspaper, webzine, or magazine news articles (opinion articles were excluded) about vaccinations, outbreaks, immunisation campaigns, vaccine research, and development
• Academic: Tweets about journal papers, academic job applications, patient recruitment, or medical/academic conferences, lectures, seminars

The researchers defined 'gatekeepers' as those Twitter actors who could potentially control the information flowing into and within a network, 'hubs' as Twitter actors that broadcast their messages to a wide audience, and 'key actors' as both hubs and gatekeepers.

In short, the study found that anti-vaccine images were predominant. By retweeting each other, anti-vaccination users increased the visibility of their images, enabling them to appear in followers' timelines and the vaccine hashtag streams more often. Hence, these images could potentially reach a broader audience than the pro-vaccine ones.

More specifically, pro- and anti-vaccination users formed two polarised networks that hardly interacted with each other and that disseminated images among their members differently. The anti-vaccination users frequently retweeted each other - strengthening their relationships, making the information redundant within their community, and confirming their beliefs against immunisation. "The high connectivity of this community may reinforce the ties between members and increase their distrust towards non-members. It may also encourage intentions to avoid vaccinating and campaigning against vaccinations....This redundancy of visual messages, combined with high level of interactions among the members..., might reinforce the network ties and indirectly encourage those on the margins of the network, who have doubts about vaccinations, to become anti-vaccine as well..." On the other hand, the pro-vaccine users formed a fragmented network, with loose but strategic connections that facilitated networking and the distribution of new vaccine information.

Moreover, while the pro-vaccine gatekeepers were non-governmental organisations (NGOs) foundations, healthcare practitioners, and academics, the anti-vaccine ones were activists, parents, parent-activists, and journalist-activists. With regard to the former, consistent with a one-way communication flow, it appears that NGOs may see Twitter primarily as a means to persuade the public of their point of view, to create networks of supporters, and for "public education" rather than for mobilisation. For instance, the NGOs shared photos about immunisation campaigns and activities they run, and their partnerships with other non-profit organisations. Their messages did not focus on vaccine safety but, rather, on their efficacy. In contrast, within the anti-vaccine community, one activist posted photos saying that vaccines are unsafe. Three of the most retweeted images included doctors' or medical associations' testimonials supporting these claims, and two of them mentioned the documentary "Vaxxed" as a reliable source of vaccine information or as a growing anti-vaccination movement.

Some practical takeaways from the research [see Related Summaries below]:

• For visual communication about vaccinations, it may be more fruitful to reach out those users searching for hashtags such as #vaccines and #vaccinations, rather than anti-vaccine actors, as the former group may be more open to information about immunisation. The World Health Organization (WHO) has given similar guidance (to reach out to a broad lay public, rather than seek to engage anti-vaccine groups) when speaking at public debates about vaccinations (WHO, 2017).
• Trying to persuade anti-vaccine users to vaccinate may not be an effective strategy, as their community is closed, possibly hostile to outsiders, and/or opposed to content produced by traditional experts and sources of information. An alternative approach could be that advanced by Lutkenhaus, Jansz, and Bouman (2019), who proposed engaging opinion leaders and gatekeepers at the border of the anti-vaccine communities (who were neither deniers nor strong supporters of vaccinations). "By engaging with them, and providing correct scientific information and data about vaccines, they were able to reach closed communities who do not trust traditional experts, but will consider provaccine messages discussed by influencers from within the community."