Responding to the surge is a major focus, partly to prevent the spread to other West African countries.
The test the US Centers for Disease Control and Prevention uses to identify clade I mpox cases is 'most likely not reliable' for detection of the substrain identified in the study, the authors say.
Another mpox study today showed that dose-sparing vaccine administration of the Jynneos vaccine appeared to have worked.
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Officials said most patients are children ages 15 and younger and that low measles vaccine coverage and malnutrition may be contributing factors.
The case-patient recently traveled abroad, but few other details were given by the institute.
Safety and immunogenicity profiles were similar to those seen in adult studies.
Health officials in the DRC are making progress with administering vaccine to high-risk people, as Nigeria expect to start its campaign next week.
A substantial proportion of mpox infections were clinically undiagnosed.
The detections push the number of African countries reporting mpox cases to 17.
Because not all viruses from mpox cases are sequenced, the findings likely underestimate the prevalence of the newly identified drug-resistant variant.
So far, more than 1,600 people have been vaccinated in some of the DRC's hot spots.
The DRC has reported more than 30,000 suspected and laboratory-confirmed mpox cases this year.
In other mpox developments, Africa CDC noted a worrying rise in Kinshasa and the WHO listed the first mpox test for emergency use.
