"A study published in December 2025 found that the strain that caused the 2022 outbreak persisted in the testes of mice for weeks after infection and caused tissue damage1, highlighting the possibility that the virus could affect male fertility. This has not yet been studied in people.

The study was posted on the preprint server bioRxiv and has not so far been peer reviewed. Meanwhile, the virus continues to evolve. In December, health officials reported a strain of the monkeypox virus that combines genetic elements of two existing types, or clades, for the first time. Although it is normal for viruses such as monkeypox to evolve, the more opportunities they are given to spread, the more likely they are to eventually evade protection from vaccines and treatments."