Figure 1

Figure 1. Epidemic curves of mpox cases among children and adolescents <18 years of age, grouped by World Health Organization regions, January 2022–May 2023. Dates represent the week of symptom onset, or...

During the study period, 1.3% (1,118/84,614) of confirmed mpox cases globally were in patients <18 years of age. Most (61.8%, 691) were from the WHO Region of the Americas, followed by the African Region (30.3%, 339), the European Region (7.5%, 84), the Eastern Mediterranean Region, (<1%, 3), and the Western Pacific Region (<1%, 1) (Figure 1). No cases in patients <18 years of age were reported from the South-East Asia Region. Countries in the African Region reported mpox cases before the global outbreak (Figure 1), whereas reports of mpox cases in Europe and in the Americas began in May 2022 and peaked in July–August 2022. In Europe and the Americas, the epidemic curve of case-patients <18 years of age closely mimics the overall regional curves (3). The global percentage of case-patients <18 years of age has consistently remained low (0%–3%). By May 2023, overall case counts were low across all regions; the Americas, the Eastern Mediterranean Region, and the Western Pacific Region reported sporadic case-patients <18 years of age. Among the 1,102 case-patients <18 years with available information, 59.3% (654) were male and 40.7% (448) female (Appendix Figure).

MPXV has 2 distinct clades, I and II (9). Virus clade information was not available for most cases and was assumed on the basis of the reporting country or subnational area and circulating clades in 2022, as reported by countries on GISAID (https://www.gisaid.org) or Nextstrain (https://nextstrain.org), in published literature, or to WHO. Of the 297 cases of mpox from countries reporting clade I, all age groups had a similar sex distribution (Appendix Figure, panel A). Of the 805 cases of mpox from countries reporting clade II, there were more male than female case-patients (269 vs. 104) among those 13–17 years of age. (For cases from Cameroon, 4 from eastern Cameroon are included in the clade I distribution, 1 from western Cameroon is included in the clade II distribution, and 1 for which we had no detailed geographic information was excluded.) Of case-patients with available hospitalization data, 47/335 (14.0%) were hospitalized and 1 was admitted to the intensive care unit; none was reported to have died.

Data on self-reported sexual behavior were limited for mpox case-patients <18 years of age. However, 37/166 (22.3%) of case-patients 13–17 years of age self-identified as men who have sex with men (MSM) (Table 1). Eleven cases involved persons living with HIV, 1 of whom was immunosuppressed. Another 6 case-patients reported immunosuppression, as defined by their care providers, that was caused by undisclosed medical conditions. Overall, 67/293 (22.9%) of cases with information provided had a stated epidemiologic link to a known mpox case.

Figure 2

Figure 2. Mpox cases by transmission type by age group among children and adolescents <18 years of age, as reported globally to the World Health Organization, January 2022–May 2023. A) Absolute numbers;...

Case-patients 0–12 years of age were exposed to MPXV mainly through physical person-to-person contact (excluding sexual contact) or contact with fomites, whereas exposure through sexual encounter was exclusively reported by those 13–17 years of age (Figure 2). Among the older group, some of whom self-identified as MSM, sexual transmission may explain the unequal sex distribution of clade II cases (Appendix Figure, panel B). The type of transmission was reported as other in 32/118 (27.1%) of cases, without additional information.

Among cases with data, 472/542 (87.1%) experienced symptoms (Table 2). We excluded from analysis cases reported to be symptomatic but without any specific symptom. The presence of any rash, which consisted of >1 rash symptoms (on the body, oral, genital, or unknown location), was the predominant symptom for all age groups (325/542, 60%); genital rash was present in 54/229 (23.6%) of case-patients 13–17 years of age and 19/313 (6.1%) of those <13 years of age (p<0.00001). Among case-patients 13–17 years of age who reported being infected through sexual contact, genital rash was present in 15/34 (44.1%). Genital rash may be indicative of the transmission route of mpox but can also be present when transmission has not occurred through sexual contact. After rash, the most reported symptoms were fever (270/542, 49.8%) and headache (158/542, 29.2%). Lymphadenopathy has been reported as a common mpox symptom (1,6); it was reported in 60/542 (11.1%) of cases in our study.

During this outbreak, countries with high caseloads reported most of the case-patients <18 years of age, however, the percentage of pediatric and adolescent patients in those countries was lower than that for adults. The percentage of patients <18 years of age was lower than had been feared early in the outbreak, amid concerns that the epidemic could shift from primarily affecting MSM to a more generalized epidemic spread, including among school-age children. Epidemiologic and clinical characteristics were similar for the age groups 0–4 and 5–12 years, whereas case-patients 13–17 years of age, who are more likely to be sexually active, commonly reported MSM sexual behavior, exposure through sexual contact, and having more genital lesions.

Studies from the Netherlands (10), Spain (11), England (12), and the United States (13,14) have described MPXV infection among children and adolescents during this outbreak. Consistent with our findings, most cases in those studies reported no intensive care unit admissions or deaths; WHO is aware of the death of an infant from mpox clade I for which data are not available (3). Our results differ from historical reports of mpox in children, in which they have been described as at higher risk for adverse events and death related to disease (15). A previous study using the same surveillance data found higher odds of hospitalization for children <5 years of age than for those 15–45 years of age (8). The lower observed severity in children and adolescents in this outbreak than for previous outbreaks may be caused by a combination of increased ascertainment of mild cases, differing access to healthcare between settings, differing health status of the host populations, and lower virulence of clade IIb MPXV; clade I MPXV infection has been reported to be associated with higher severity than clade II (1).

Our study is based on surveillance data and likely underestimates the true number of case-patients <18 years of age, particularly in Africa (8). Disease severity may be underestimated because countries may not have updated case outcomes if hospitalization or death was delayed. Finally, data completeness varied among regions and countries; thus, our results may not be representative of each setting.

This study highlights the need for thorough epidemiologic investigation of mpox in children and adolescents. Clinicians should consider mpox as a possible diagnosis in these age groups when they have indicative symptoms, even with no known epidemiologic link to another case.