The anti-vaccine movement has gained traction in many countries since the COVID-19 pandemic began. However, their aggressive behaviour through replies on Twitter—a form of directed messaging that can be sent beyond follow-follower relationships—is less understood, and even less is known about the language use differences of this behaviour. We conducted a comparative study of anti-vaxxers’ aggressive behaviours by analysing a longitudinal dataset of COVID-19 tweets in English and Japanese. We found two common features across these languages. First, anti-vaxxers most actively transmit targeted messages or replies to users with different beliefs, especially to neutral accounts, with significantly toxic and negative language, and these replies are often directed to posts about vaccine operations. Second, influential users with many followers and verified accounts are more likely to receive the most toxic replies from the anti-vaxxers. However, pro-vaccine accounts with a few followers receive highly toxic replies in English, which is different from the Japanese case. These results provide insights into both language-dependent and independent countermeasures against anti-vaxxers’ aggressive behaviour.

自 COVID-19 大流行开始以来，反疫苗运动在许多国家都受到了关注。然而，他们通过在 Twitter 上回复的攻击性行为——一种可以在追随者关系之外发送的定向消息形式——却鲜为人知，甚至对这种行为的语言使用差异知之甚少。我们通过分析英文和日文 COVID-19 推文的纵向数据集，对反 vaxxers 的攻击行为进行了比较研究。我们在这些语言中发现了两个共同特征。首先，反疫苗者最积极地向具有不同信仰的用户发送有针对性的信息或回复，尤其是对中立的账户，使用明显有毒和负面的语言，这些回复通常针对有关疫苗操作的帖子。第二，拥有许多追随者和经过验证的帐户的有影响力的用户更有可能从反疫苗者那里收到最有毒的回复。然而，有少数追随者的支持疫苗的账户会收到高度有毒的英文回复，这与日本的情况不同。这些结果提供了对针对反疫苗者攻击性行为的语言依赖和独立对策的见解。