The purpose of this study is to review the discourse on vaccination from a critical perspective by considering coronavirus disease 2019 (COVID-19) news on web portals to be practical arguments advocating for certain actions. For this purpose, this study analyzed the argument patterns of the discourse on vaccination with the keyword COVID-19 vaccine side effects and examined discourse characteristics highlighted by media reports to evaluate their meaning. Contrasting patterns were observed between pro- and anti-vaccine arguments, which consisted of the necessity of vaccination and medical evidence and which focused on personal choice and vaccine side effects, respectively. The characteristics of the political discourse were observed in the contest between these arguments. Rhetorical phrases, which are often used in the political discourse, represented the misleading arguments that lacked evidential accuracy and argumentative validity by maximizing fear, instead of alleviating fear about a health crisis with scientific information and discussion. As fake news trending on social media was introduced to online news portals, which are regarded as public discourse platforms, and undermined trust in the public discourse, it served as an opportunity to politicize the discourse on vaccination.