Can Mpox Spread Without Symptoms? New Study Reveals Shocking Findings

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A new study published in Nature Communications suggests that mpox can be transmitted by individuals who show no symptoms, challenging previous assumptions about the virus’s spread. Researchers found that 1% of men who have sex with men (MSM) tested positive for mpox during routine sexually transmitted infection (STI) screenings despite reporting no symptoms. Genetic analysis confirmed that these asymptomatic individuals likely transmitted the virus to sexual partners, according to the study.

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What Does the Study Reveal?
The research, conducted at Kaiser Permanente in Los Angeles, involved nearly 8,000 MSM undergoing STI testing between 2022 and 2023. Of those, 1% tested positive for mpox without experiencing symptoms such as fever, fatigue, or skin lesions. Scientists estimated that only 1 in 33 mpox infections are diagnosed, highlighting a significant gap in detection. The study’s lead author, Joseph A. Lewnard, an associate professor of epidemiology at the University of California, Berkeley, noted that asymptomatic transmission complicates outbreak tracking.

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How Does Mpox Spread?
Mpox, caused by the orthopoxvirus, typically presents with flu-like symptoms and a rash that may resemble herpes or syphilis. While not classified as a sexually transmitted infection (STI), it spreads through close skin-to-skin contact, including during sexual activity. The virus can also transmit via contaminated clothing, towels, or bedding. During the global outbreak that began in May 2022, gay and bisexual men, other MSM, and transgender individuals were disproportionately affected.

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Why Is Asymptomatic Transmission Significant?
Contact tracers previously struggled to link diagnosed cases to new infections, a challenge the study may now explain. By identifying asymptomatic carriers, researchers suggest that transmission chains are harder to trace, potentially leading to undetected spread. The study’s genetic analysis of mpox samples revealed patterns indicating that asymptomatic individuals contributed to outbreaks, according to the authors.

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What Is the Role of Vaccination?
The mpox vaccine, JYNNEOS, reduced the risk of infection by 50% in the study. The Centers for Disease Control and Prevention (CDC) recommends the two-dose vaccine for individuals at higher risk, including MSM and transgender people who have engaged in specific behaviors, such as having multiple partners or attending large public events in areas with active transmission. Partners of at-risk individuals and those with weakened immune systems, including people with HIV, are also advised to get vaccinated.

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What Are the Implications for Public Health?
Despite vaccination campaigns during the 2022 outbreak, vaccination rates have declined since. Lewnard emphasized that unvaccinated individuals face a heightened risk of severe disease, as the study’s findings suggest the virus’s transmissibility is greater than previously understood. The CDC has not yet updated its guidance based on this research, but the study’s authors call for renewed efforts to boost vaccination rates.

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What Do Experts Say?
Dr. Sarah M. Bower, an infectious disease specialist at the University of Washington, noted that the study underscores the importance of expanded testing and education. “Asymptomatic transmission means we need to rethink how we monitor and prevent mpox,” she said. The American Sexual Health Association, which cited the study in its 2026 report, highlighted the need for increased awareness about safe sex practices and regular STI testing.

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What Should Individuals Know?
Health officials advise individuals to practice safer sex by using barriers like condoms during anal or oral sex, avoiding close contact with people showing symptoms, and getting tested regularly. The CDC also recommends that anyone experiencing a rash or flu-like symptoms seek medical attention. For those unsure about their risk, consulting a healthcare provider about vaccination is strongly encouraged.

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“Unvaccinated people face risk of severe disease if they are exposed to mpox, and our findings suggest this risk is greater than we previously understood.”
SourceJoseph A. Lewnard, PhD, lead author of the study and associate professor of epidemiology at the University of California, Berkeley.

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The study’s findings align with broader public health concerns about underdiagnosed infectious diseases. In 2023, the World Health Organization reported that 20% of mpox cases globally went unrecorded, a figure that may now be underestimated. As researchers continue to analyze asymptomatic transmission, health agencies are urged to adapt strategies for prevention and education.

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For more information on mpox, vaccination, and safer sex practices, individuals are encouraged to consult the CDC’s website or contact their local health department.