Rapid spread of MPXV clade Ib with high genetic relatedness among men who have sex with men, Berlin, Germany, week 50 2025 up to week 10 2026

Following the first detection of monkeypox virus (MPXV) clade Ib in Berlin, Germany, in December 2025, clade Ib rapidly predominated over clade IIb among notified mpox cases. The 35 clade Ib cases were primarily due to autochthonous transmission, with high genetic relatedness among strains circulating in men in Berlin, despite no identified epidemiological links. Sexual contact between men was reported as a potential source of infection in 28 cases, while for the remaining seven cases this information was unknown.