A new study uncovers “silent” mpox circulation in Nigeria, while another concludes that 58% of mpox patients still have signs or complications up to 1.5 years after diagnosis.

‘Immune footprints’ that elude surveillance

For the first study, published today in Nature Communications, researchers from the University of Cambridge and Nigeria analyzed stored blood samples from 176 healthy Nigerian adults who had participated in COVID-19 vaccine studies, including health care workers sampled in 2021 and community volunteers sampled in 2023. Participants hadn’t received mpox or smallpox vaccines as adults and had no known exposure to mpox.

The team measured responses to six different mpox virus antigens, or structural parts of the virus to which the immune system responds, allowing detection of both the strength and scope of immune responses.

“While most public health attention has focused on symptomatic mpox cases, little is known about how often people may be exposed to the virus without developing classical disease,” the study authors noted.

At baseline, 14% of participants had antibody profiles consistent with immunity derived from smallpox vaccination. Most of these participants were born before 1980, meaning that they were more likely to have been vaccinated during childhood. Their antibody responses were strong and broad, recognizing several mpox antigens even decades after smallpox vaccination campaigns ended.

But to the researchers’ surprise, five of 153 participants (3%) with follow-up samples collected roughly nine months after baseline had clear evidence of new immune responses indicative of recent mpox exposure—but no symptoms. These adults had no documented mpox diagnosis and did not report compatible illness, suggesting exposure without recognized disease.