Alexei Navalny, Russia’s most prominent opposition figure, has been taken to a hospital from jail after reportedly suffering an allergic reaction. Navalny was in jail for organizing unauthorized protests against the exclusion of opposition candidates from local elections. Russian police arrested nearly 1,400 demonstrators in front of Moscow’s city hall on Sunday, the largest detainment in more than a decade. Navalny first made his name as an anti-corruption leader for organizing Russia’s biggest street protests against President Vladimir Putin in 2011. Navalny’s spokeswoman, Kira Yarmysh, wrote on Twitter that he had been hospitalized on Sunday with “severe swelling of the face and skin redness,” adding that the cause was unknown and that “he had never suffered from such reactions in the past.”