Epidemiologic and Clinical Features of Mpox in Adults Aged 50 Years — United States, May 2022–May 2023

Mpox might affect multiple organ systems; therefore, persons with comorbidities, including HIV and immunocompromising conditions, which are more prevalent among adults aged >50 years, might be at increased risk for more severe mpox disease (4). Most deaths and hospitalizations among adults with mpox in the United States during the recent outbreak occurred in persons with immunocompromising conditions (5,6). In this report, however, excluding adults who had received JYNNEOS vaccine, the prevalences of hospitalization and death among adults aged >50 years with mpox were similar to those in persons aged 18–50 years, and the prevalences of some symptoms were lower among adults aged >50 years than among those aged 18–50 years. Although the reasons for this finding are not clear, receipt of smallpox vaccine as part of childhood immunization before routine smallpox vaccination discontinued in the United States in 1971 might confer some level of protection against mpox in the current outbreak, with respect to whether the clinical presentation was atypical or asymptomatic (7).

The prevalences of pruritus, constitutional symptoms, and hospitalizations were lower among adults with mpox aged >50 years who received JYNNEOS vaccine than among those who did not receive the vaccine. Although childhood smallpox vaccination might confer some protection against monkeypox virus infection and might mitigate mpox disease severity, it is likely that receiving the currently recommended JYNNEOS vaccine provided additional protection. This finding is consistent with a study among adults who received JYNNEOS vaccine, wherein adults who received ≥1 dose of JYNNEOS vaccine had lower rates of hospitalization and symptoms (8). This finding underscores the importance that persons at risk for mpox, particularly adults aged >50 years, receive currently recommended JYNNEOS vaccination. Immunologic studies have demonstrated some long-term immunologic memory from childhood smallpox vaccination that is cross-protective against mpox (7,9), but such immunity might have waned (7). JYNNEOS vaccination is recommended for all adults who are at risk for mpox irrespective of receipt of childhood smallpox vaccination (10).

Limitations

The findings in this report are subject to at least four limitations. First, data for some variables, such as HIV status, presence of immunocompromising conditions and mpox symptoms, and JYNNEOS vaccination status were frequently missing in national case surveillance data, which limits full characterization of the epidemiologic and clinical features among adults with mpox and could contribute to confounding bias. Second, some variables were self-reported, and might be subject to recall and social desirability biases. Third, receipt of smallpox vaccination was assumed for all adults aged >50 years despite nuances in implementation in the United States and other countries of origin of adults with mpox. Finally, this analysis was limited to confirmed and probable mpox cases reported to jurisdictional public health departments and might not represent all adults with mpox.

Implications for Public Health Practice

Hospitalization was less likely among adults aged >50 years with mpox who had received JYNNEOS vaccine than among those who had not. All adults who are at risk for acquiring mpox, regardless of childhood smallpox vaccination status, should receive 2 doses of JYNNEOS vaccine (10).