What changed? From suspicion to near-certainty
For decades, researchers suspected a link between Epstein-Barr virus (EBV) and multiple sclerosis (MS) because people who had infectious mononucleosis (caused by EBV) were at higher risk. But correlation isn't causation. The game-changer came in 2022 from a massive longitudinal study of over 10 million US military personnel [5]. Researchers tracked 955 people who developed MS and found that the risk of MS shot up 32-fold after they became infected with EBV. No other virus, including the similarly transmitted cytomegalovirus, showed any such increase. This study is the strongest of its kind because it followed healthy people over time and watched what happened after EBV infection, making it hard to argue that something else caused both the infection and the disease.
A separate 2022 study of over 2.5 million Danes added a different kind of evidence [1]. It showed that having siblings—especially younger siblings close in age—protected against both infectious mononucleosis and MS. The logic: siblings expose each other to EBV early in childhood, when the infection is usually mild and doesn't trigger the immune problems linked to MS. Each younger sibling (0–2 years younger) reduced MS risk by about 20% (hazard ratio 0.80). This pattern strongly suggests that the timing of EBV infection matters: catching it early is protective, catching it late is dangerous.
How might EBV actually trigger MS?
The leading theory is that in some people, the immune response to EBV goes wrong and starts attacking the brain and spinal cord. One study found that MS patients have higher levels of antibodies that cross-react—they recognize both an EBV protein (EBNA386-405) and a protein in the brain called GlialCAM370-389 [6]. This is called molecular mimicry: the immune system learns to attack EBV, but then mistakenly attacks similar-looking brain tissue. The same study showed that people who don't develop MS have natural killer (NK) cells and T cells that can eliminate these cross-reactive, autoreactive cells. But in people with certain genetic variations, this cleanup fails, and the risk of MS increases up to 260-fold.
Another study found that a specific EBV gene, LMP2A, is more frequently detected and more active in the blood of MS patients compared to healthy controls [2]. LMP2A is a protein that helps EBV hide inside B cells (a type of immune cell) and keep them alive longer. This could mean that in MS patients, EBV is not just a past infection but is actively influencing immune cells in a way that promotes disease. A 2025 study using genetic data identified 21 genes that overlap between EBV's interactions with human cells and MS risk genes, and found that some of these genes are abnormally active in brain cells (astrocytes and microglia) of MS patients [3]. This provides a molecular bridge between the virus and the brain damage seen in MS.
What does this mean for treatment and prevention?
If EBV is the necessary trigger for MS, then preventing or treating EBV infection could prevent or treat MS. A 2023 review [4] and the 2022 Danish study [1] both explicitly suggest that an EBV vaccine given before the teenage years could essentially eradicate MS. This is not science fiction—vaccine development is already underway. The same review also discusses using antiviral drugs against EBV as a potential treatment for people who already have MS, though this is still experimental.
The 2023 study on immune control [6] also points to a more immediate possibility: identifying people at high risk for MS based on their genetic makeup and their immune response to EBV, and then monitoring them closely or intervening early. The study found that specific combinations of host genes and EBV variants were associated with up to a 260-fold increased risk of MS. This kind of precision risk assessment could one day guide personalized prevention strategies.
About These Sources
This answer is built on 6 peer-reviewed studies — published from 2022 to 2025, 2 from 2024 or later, 5 in Q1 journals, collectively cited 2,220 times — selected as the most relevant from 7 studies that passed quality screening, drawn from 45 papers retrieved from a database of over 500 million.
Sources used in this answer
Siblings reduce multiple sclerosis risk by preventing delayed primary Epstein–Barr virus infection
In a nationwide cohort of 2.5 million Danes, having siblings—especially younger siblings close in age—reduced the risk of both infectious mononucleosis and multiple sclerosis, supporting the idea that early EBV infection protects against MS. A younger sibling (0–2 years younger) reduced MS risk by 20% (hazard ratio 0.80).
EBV and multiple sclerosis: expression of LMP2A in MS patients
In 57 MS patients and 49 healthy controls, the EBV gene LMP2A was significantly more frequently detected and more highly expressed in MS patients, suggesting active viral involvement in the disease.
Exploring the role of EBV in multiple sclerosis pathogenesis through EBV interactome
Using public genetic datasets, the study identified 21 genes shared between EBV's interactions with human cells and MS risk genes, and found that some of these genes are abnormally expressed in brain cells of MS patients.
Epstein–Barr virus as a leading cause of multiple sclerosis: mechanisms and implications
This comprehensive review concludes that epidemiological evidence now shows MS is a rare complication of EBV infection, and discusses mechanisms (molecular mimicry, immune dysregulation) and implications for vaccines and antivirals.
Longitudinal analysis reveals high prevalence of Epstein-Barr virus associated with multiple sclerosis
In a longitudinal study of over 10 million US military personnel (955 with MS), the risk of MS increased 32-fold after EBV infection, but not after other viruses. Neurofilament light chain (a marker of nerve damage) rose only after EBV seroconversion.
Ineffective control of Epstein-Barr-virus-induced autoimmunity increases the risk for multiple sclerosis
The study showed that EBV-specific antibodies cross-react with a brain protein (GlialCAM), and that people who fail to eliminate these cross-reactive cells due to specific genetic and viral factors have up to a 260-fold increased risk of MS.