Mono doesn’t directly cause multiple sclerosis, but the virus behind it is now considered a necessary step in developing the disease. A landmark 2022 study tracking over 10 million U.S. military recruits found that infection with Epstein-Barr virus (EBV), the virus that causes mono, increased the risk of MS by 32-fold. No other virus showed a similar effect. Nearly all MS patients carry EBV antibodies, compared to about 90% of the general population, meaning almost no one develops MS without first being infected.
That said, over 90% of adults worldwide have been infected with EBV, and only a tiny fraction ever develop MS. So EBV appears to be required but not sufficient on its own. Other factors, including your genes and environment, determine whether the virus eventually triggers the disease.
How the Virus Tricks the Immune System
Once you catch EBV, it never fully leaves your body. It goes dormant inside certain immune cells and stays there for life. In most people, this causes no problems. But in those who eventually develop MS, something goes wrong with how the immune system remembers the virus.
Research published in Nature Immunology identified a case of mistaken identity at the molecular level. One of EBV’s proteins looks structurally similar to a protein called GlialCAM, which sits on the surface of cells that insulate nerve fibers in the brain and spinal cord. Antibodies originally made to fight EBV can, over time, start attacking GlialCAM instead. This friendly fire strips the protective coating from nerves, which is the hallmark damage seen in MS. The resemblance between the viral protein and the nerve protein is what researchers call molecular mimicry, and it explains how a common childhood infection could, years later, set off an autoimmune disease in the brain.
Why Getting Mono as a Teenager Matters More
Most people catch EBV in early childhood without ever knowing it. When infection happens later, during adolescence or young adulthood, it’s more likely to cause the classic symptoms of mono: extreme fatigue, sore throat, swollen glands. That symptomatic infection also appears to carry a higher MS risk.
A sibling-based study published in JAMA Network Open found that infectious mononucleosis during adolescence was associated with roughly a threefold increase in MS risk, even after accounting for shared family genetics. Childhood mono carried a similar elevated risk, around 2.9 times higher than unaffected siblings. The adolescent window seems to be a period of particular vulnerability, possibly because a stronger immune response to the virus at that age creates more of the cross-reactive antibodies that later target nerve tissue.
The Long Gap Between Infection and MS
MS doesn’t show up right after mono. The 2022 military study tracked recruits over a 20-year period and found that EBV infection consistently preceded MS diagnosis, often by many years. Nerve damage appears to begin silently well before symptoms like numbness, vision problems, or difficulty walking emerge. Blood markers of nerve fiber breakdown were elevated in people who would later be diagnosed with MS, suggesting the disease process starts long before anyone notices something is wrong.
This long latency period is one reason the connection between mono and MS took so long to confirm. By the time someone is diagnosed with MS in their 30s or 40s, their bout of mono at 16 feels like ancient history.
Genetics and Vitamin D Play a Role Too
The strongest genetic risk factor for MS is a specific immune system gene called HLA-DRB1*15:01. About 25-30% of MS patients carry this variant. Recent research has shown that this gene actually functions as a co-receptor for EBV, meaning it helps the virus enter immune cells more efficiently. People who carry this gene variant and get infected with EBV face a compounded risk: the gene makes EBV infection more impactful, and EBV infection in turn drives the autoimmune process. This is a clear example of how genetic and environmental risk factors link together mechanistically rather than just statistically.
Vitamin D deficiency is another independent risk factor. Low vitamin D levels are associated with reactivation of dormant EBV, while adequate vitamin D helps the immune system keep the virus suppressed. Vitamin D supplementation has been shown to reduce EBV reactivation, which may partly explain why MS is more common in northern latitudes where sunlight exposure is limited. If you’ve had mono and are concerned about MS risk, maintaining healthy vitamin D levels is one of the few modifiable factors currently supported by evidence.
What This Means for Prevention
The discovery that EBV is a prerequisite for MS has opened a new path toward prevention and treatment. Moderna is currently running a Phase 2 clinical trial of an mRNA-based therapy (mRNA-1195) in people aged 18 to 55 who already have MS and are EBV-positive. The trial is testing whether targeting EBV can reduce relapses and slow disability progression over roughly two and a half years. This is a treatment study, not a vaccine for preventing initial infection, but it reflects how seriously the field now takes the EBV connection.
Separate efforts to develop a preventive EBV vaccine are also underway. If a vaccine could prevent EBV infection in the first place, it could theoretically eliminate the single most important environmental trigger for MS. That possibility, once speculative, now rests on strong evidence that virtually no one develops MS without first encountering this virus.