Anti-vaccine attitudes pose a threat to public health by impeding the development of herd immunity. However, the proliferation and politicization of anti-vaccine discourse, exacerbated by the pandemic and the rise of social media, have not been fully elucidated. This study, using Japanese Twitter data, revealed that (a) anti-vaxxers are characterized by high political interest, (b) persistent anti-vaxxers were more ideologically left-leaning and had stronger ties to existing political parties, and (c) pandemic-induced new anti-vaxxers displayed low political engagement but a greater affinity for conspiracy theories, spirituality, naturalism, and alternative health practices, which served as gateways to anti-vaccination views. Furthermore, those who turned anti-vaccine after the pandemic also exhibited an increased tendency to follow the newly emerged anti-vaccine party, potentially contributing to their political representation at the national level. These analyses show that the anti-vaccine discourse has expanded and reached a politically representative scale, strengthening its discursive network with conspiracy theories, spirituality, naturalism, and alternative health practices.