Prolonged Monkeypox Virus Infections, California, USA, May 2022–August 2024

Monkeypox virus (MPXV) infection typically lasts 14-28 days. Prolonged MPXV infection, in which symptoms or test positivity last >28 days, has been documented but not fully characterized. We used the California Department of Public Health (California, USA) mpox registry to compare prolonged (>28 days) and nonprolonged (<28 days) mpox cases by demographics, HIV status, and JYNNEOS vaccination status. Of 6,469 cases, 82 (1.3%) were prolonged. Persons with prolonged MPXV infections were more likely to be Black or African American (prolonged, 20.7%, vs. nonprolonged, 11.6%) and to have HIV (prolonged, 61.0%, vs. nonprolonged, 39.9%). Among persons with HIV, prolonged infections were more likely among those with lower (<200) CD4 counts (prolonged, 10.0%, vs. nonprolonged, 3.9%) or not engaged in HIV care (prolonged, 46.0%, vs. nonprolonged, 18.1%). No prolonged infections occurred in persons who received 2 JYNNEOS vaccine doses. Groups disproportionately affected by prolonged mpox should be prioritized for mpox vaccine education and outreach.