A disease that went from overlooked to urgent
For decades, mpox (formerly called monkeypox) was considered a rare disease mostly confined to remote areas of Central and West Africa. That changed dramatically in 2022, when a global outbreak triggered the first of two Public Health Emergencies of International Concern declared by the World Health Organization — the highest level of global health alarm.
Understanding who has been infected, who has recovered, and who remains vulnerable is central to controlling any outbreak. But in places where mpox has circulated for years, that understanding has been surprisingly hard to pin down.
The diagnostic gap in endemic regions
During an active mpox infection, PCR testing (the same technology used widely during COVID-19) can confirm the virus is present. But PCR only works during the active phase of illness.
Serology — blood tests that detect antibodies (proteins the immune system makes after exposure to a pathogen) — can reveal past infections. This matters enormously for tracking how many people in a community have some level of protection, even if they never had a confirmed diagnosis.
The catch? Most serological tests for mpox were designed and calibrated during the 2022 global outbreak, using samples from people in Europe and North America. They were never validated for use in a place like the Democratic Republic of the Congo (DRC), where the virus has been present for generations, where smallpox vaccination was historically widespread, and where other closely related poxviruses may also have circulated.
Old tools, new setting
Tests built for one population don't always work the same way in another. In the DRC, a blood sample might show antibody reactivity for several reasons: the person survived mpox, they received an older smallpox vaccine, they were exposed to another orthopoxvirus (a related family of viruses), or they received a newer mpox vaccine.
Without context-appropriate cutoff values — the thresholds that separate a truly positive result from background noise — a serological test can produce misleading answers.
Think of it like calibrating a bathroom scale. A scale designed in one country may use different units than expected in another. The underlying measurement is the same, but without the right reference point, the reading is meaningless.
What researchers tested
Scientists analyzed blood samples from 134 individuals divided into six distinct groups with different exposure histories — including mpox survivors, people vaccinated against smallpox decades ago, people who received newer mpox vaccines, and unexposed individuals. All samples were tested against five antigen pairs from mpox and the related vaccinia virus using a laboratory platform called Mesoscale Discovery, which can measure multiple targets in a single small blood sample.
Three antigens stood out as the best performers for distinguishing true mpox survivors from everyone else: E8L, A35R, and B6R. When the results from all three were evaluated together using a composite scoring rule, the panel showed clear separation between mpox survivors and individuals with other types of orthopoxvirus exposure.
Specific numerical cutoff values were established for each antigen — the minimum signal level at which a sample is considered positive for mpox exposure. These cutoffs are designed for the DRC context specifically, accounting for the complicated immune histories that people in endemic settings carry.
This is not a new treatment or a vaccine — it is the calibration work that makes surveillance science reliable in the places that need it most.
Knowing who has immunity in a community is the foundation of outbreak response. It tells public health officials where vaccination campaigns should be focused, whether natural immunity is spreading, and whether certain populations have been hit harder than official case counts suggest.
In a region where health infrastructure is strained and many cases go undetected, a validated serological tool could help fill major gaps in the data.
If you live outside the DRC or another mpox-endemic area, this research does not directly change what you should do. The practical implication for most readers is indirect: better surveillance in endemic regions helps the global community detect and respond to mpox threats earlier, before they spread.
If you have questions about mpox vaccination or your own exposure risk, your local health department or physician is the right resource.
Limitations to keep in mind
This was a small study — just 134 individuals — which means the cutoff values established here will need to be validated in larger, more diverse cohorts. The six exposure groups were defined based on available samples, not a randomly selected population. And the Mesoscale Discovery platform used here is a laboratory instrument, not a rapid field test — deployment in remote areas would require additional adaptation.
Road ahead
The researchers plan to validate these cutoff values in larger population-based studies in the DRC and possibly other endemic countries. The longer-term goal is to integrate a validated serological panel into mpox surveillance systems, helping health authorities build a clearer, more accurate picture of where immunity exists and where gaps remain.
