This study examined mpox in nearly 20,000 people living with HIV across the United States and found that those who were not taking HIV medications, had uncontrolled HIV, or had recent sexually transmitted infections were at greater risk of getting mpox and being hospitalized. The researchers also found that the mpox vaccine was highly effective at preventing infection and severe illness, including among people with weakened immune systems. However, some groups, particularly Black people living with HIV, were less likely to receive the vaccine. The authors conclude that increasing vaccine access and prioritizing people with uncontrolled HIV or low CD4 counts could help reduce serious mpox related illness and hospitalization.