Anti-vaccine trolling on video-hosting websites hinders efforts to increase vaccination rates by using toxic language and threatful claims to intimidate people and promote vaccine hesitancy. However, there is a shortage of research investigating the effects of toxic messages on these platforms. This study collected YouTube anti-vaccine videos and examined the relationship between toxicity and fear in the comment section of these videos. We discovered that highly liked toxic comments elicited a significant level of fear in subsequent comments of the same videos. Moreover, we found intricate contagions across toxicity and fear within the comments. These findings suggest that initial troll comments can evoke negative emotions, which may fuel vaccine hesitancy on social media. Our research bears essential implications for managing public health messaging and online communities, particularly in moderating fear-mongering messages about vaccines.