Examining Sentiments and Popularity of Pro- and Anti-Vaccination Videos on YouTube

Vaccine misinformation on social media poses significant drawbacks to the efforts of vaccine coverage rates. This research studies the interlinkages between pro- and anti-vaccine YouTube videos to help public health professionals explore new ways to reach anti-vaccine and vaccine-hesitant audiences. Using YouTube's API, we retrieved 9,489 recommended videos from 250 seeds using keywords such as "vaccines" and its derivatives. We then manually identified 1,984 videos directly related to vaccination and then categorized their vaccine sentiment into pro-, anti-, and neutral. Results show that 65.02% of the videos were anti-vaccine, and only 20.87% were pro-vaccine, 14.11% were neutral. Anti-vaccine videos were significantly more prevalent in the "News & Politics" and "People & Blogs" video categories; while pro-vaccine videos were more prevalent in the "Education" and "Science & Technology" categories. Results also showed that anti-vaccine sentiment videos have higher values of closeness centrality (p<0.05), suggesting that watching an anti-vaccine video will likely lead to more anti-vaccine video recommendations. Moreover, videos that had more dislikes than likes (dislike/like ratio) are positively related to pro-vaccine videos (OR=3.912), suggesting that pro-vaccine videos are more ill-received on YouTube than anti-vaccine videos. This study is the first to examine the network of vaccine-related videos on YouTube and their centralities. The results highlight some possible limitations of YouTube-based vaccination awareness campaigns and also emphasize the need to diversify how YouTube makes its recommendations to help viewers break out of the anti-vaccine "bubble."