Most of us got “mono” and moved on. Felt awful for a few weeks, missed some school or work, and eventually recovered. The Epstein-Barr virus – the culprit behind that exhausting spell – seemed like a chapter we’d firmly closed. What science is now discovering is that for many people, that chapter may not be as finished as it appeared. The virus is still in there. And researchers are increasingly asking what else it might be doing.
This isn’t a niche medical curiosity. Epstein-Barr virus is the most common and persistent human virus, affecting roughly 95 percent of the global population with a lifelong asymptomatic infection. Most people pick it up in childhood and never feel a thing. Some get hit with infectious mononucleosis – the notorious “kissing disease” – as teenagers or young adults. Either way, even when it causes no symptoms or mild symptoms, EBV stays in the body forever.
That permanence is what has scientists paying close attention. A virus that never fully leaves isn’t just a dormant passenger. It may be quietly influencing health outcomes across decades. The research coming out of major institutions right now is both striking and, for most parents, entirely under the radar.
What EBV Actually Is
Exactly 60 years ago, pathologist Anthony Epstein and virologist Yvonne Barr announced the discovery of a virus that has carried their names ever since. The Epstein-Barr virus made scientific history as the first virus proven to cause cancer in humans. It belongs to the herpesvirus family – the same broad group that includes chickenpox and cold sores – and it behaves like a classic herpesvirus in one important way: once it’s in, it stays in.
About 90 percent of the adult population are infected with the virus, usually experiencing no symptoms and no resulting illness. Around 50 percent become infected before the age of five, but many people don’t catch it until adolescence. That timing matters more than most people realize. The risk of both infectious mononucleosis and multiple sclerosis increases when primary EBV infection occurs after the age of 10.
Acute infection with the virus can cause glandular fever – also known as “the kissing disease” – and can put infected individuals out of action for several months. But the long game is what concerns researchers. EBV doesn’t just cause mono and leave. It settles into a specific type of immune cell – B cells, which form a core part of the body’s defense system – and persists there for life, cycling between dormancy and low-level reactivation.
The Cancer Connection
EBV has been classified as a Group I carcinogen by the International Agency for Research on Cancer since 1997. That classification means the evidence for its role in causing cancer in humans is considered definitive by international health authorities – not theoretical, not emerging, but established. The question researchers have been working to answer is exactly how wide that role extends.
A major 2025 study published in Nature Communications gave the clearest answer yet. Researchers investigated the link between EBV antibody levels and cancer risk in two large prospective cohorts from Southern China, comprising 73,939 adults. During around 8 to 10 years of follow-up, 964 and 1,026 incident cancer cases were identified in the two cohorts.
The findings were significant. Individuals who tested positive for EBV antibodies were found to have a higher risk of developing cancers such as lung cancer, liver cancer, nasopharyngeal carcinoma, and lymphoma. The association wasn’t subtle. People with detectable EBV antibodies were nearly five times more likely to develop cancer overall compared to those without them, according to the study’s pooled analysis. The study also revealed a dose-response relationship, in which higher levels of antibodies were associated with increased cancer risk. This elevated risk persisted even up to 10 years before diagnosis, suggesting that EBV infection may play a long-term role in cancer development.
What this means practically: a blood test measuring EBV antibody levels could, in theory, help identify people at elevated cancer risk long before symptoms appear. The study estimated that 7.8 percent of the total cancer burden in Southern China could be attributed to EBV antibody seropositivity.
The International Agency for Research on Cancer, which co-led the research, called the findings notable for their scope. This wasn’t confirmation of a known EBV-linked cancer type, but evidence of association across a much broader range of malignancies than previously understood.
How does the virus actually do this? One mechanism is epigenetic modification of the host genome in a way that promotes unregulated tumor growth. This is primarily accomplished by histone modification and DNA hypermethylation. These alterations serve various purposes in promotion of tumor growth, such as downregulating tumor suppressor genes, reducing normal protein transcription, and inactivating DNA repair enzymes. Think of it like the virus quietly editing the body’s own instruction manual, turning off the sections that stop cells from growing out of control.
A separate line of research, funded by the NIH and published in Nature, identified another mechanism. A key viral protein readily binds to a particular spot on a particular human chromosome. Where the protein accumulates, the chromosome becomes more prone to breaking. Fragile chromosomes, over time, are one of the known precursors to cancer. The NIH Director’s Blog noted that this discovery could fuel development of new ways to screen for and identify those at elevated risk of EBV-associated cancers.
Importantly, the American Cancer Society is clear that most people who’ve had mono will not develop an EBV-related cancer. But knowing your risk can help you watch for signs, especially if you have more than one risk factor. EBV is one piece of a complex picture that also includes genetics, age, geography, and other environmental factors.
The Multiple Sclerosis Bombshell
If the cancer findings were striking, the MS research has been genuinely stunning – and it keeps getting stronger.
Multiple sclerosis (MS) is an autoimmune disease where the immune system attacks the protective coating around nerve fibers, disrupting signals between the brain and body. MS is a long-term autoimmune condition that affects nearly one million people in the United States. For decades, researchers knew it was triggered by some combination of genetics and environment, but the environmental piece remained frustratingly unclear.
Then came a landmark 2022 study from Harvard T.H. Chan School of Public Health that changed the conversation. To determine the connection between EBV and MS, the researchers conducted a study among more than 10 million young adults on active duty in the U.S. military and identified 955 who were diagnosed with MS during their period of service. The team analyzed serum samples taken biennially by the military and determined the soldiers’ EBV status at time of first sample.
In this cohort, the risk of MS increased 32-fold after infection with EBV but was unchanged after infection with other viruses. That is not a typo. Thirty-two times the risk. For comparison, the link between smoking and lung cancer – often cited as one of the clearest cause-and-effect relationships in all of medicine – involves roughly a 25-fold increased risk in heavy smokers. The EBV-MS association is in that same territory.
800 of 801 MS cases occurred in individuals who had previously tested positive for EBV. Thirty-five of those individuals had tested negative upon their first donation, and all but one then became positive prior to their MS symptoms emerging. Crucially, the researchers found no such association between MS and any other human viruses – including cytomegalovirus, a virus distantly related to EBV that is transmitted similarly. The specificity of the finding is part of what makes it so compelling.
Epidemiologic data now indicate that EBV is a requisite risk factor for the development of MS. In plain terms: you essentially cannot develop MS without having first been infected with EBV. The mechanisms, however, are still being worked out, and that distinction matters. Necessary but not sufficient. Most people with EBV don’t develop MS, which means other factors – likely genetic – also play a role.
Research published in PNAS in 2025 found EBV markers specifically inside MS brain lesions. EBV markers, particularly EBNA1 and LMP1, were enriched within MS lesions. EBV-positive cells interact closely with reactive astrocytes, microglia, and neurons. Image analysis confirmed the presence of EBV-positive staining within neurons and glial cells, suggesting a direct role for EBV in neuronal and glial involvement in MS.
A 2026 study from UC San Francisco, published in Nature Immunology, added another piece to the puzzle. The study shows that people with MS have higher levels of certain CD8+ “killer” T cells – immune cells that normally destroy infected or damaged cells. Some of the elevated killer T cells specifically respond to EBV, suggesting the virus may help set off the harmful immune activity seen in MS.
One leading theory for how EBV triggers MS is molecular mimicry, where the virus produces proteins that look similar enough to proteins in the brain and spinal cord that the immune system, trained to attack EBV, accidentally attacks those too. It’s a case of friendly fire, set in motion years or even decades earlier by a virus the body thought it had dealt with. If you want to understand more about how viral infections can have lasting effects on children’s developing immune systems, this piece on traits inherited from mothers looks at how early microbial exposures shape long-term health.
What’s Being Done About It
Here’s where things get genuinely hopeful. The strength of the EBV-MS evidence has directly accelerated the race for an EBV vaccine – and it’s further along than most people know.
A clinical trial is now recruiting participants to test whether an experimental vaccine for EBV is safe and may help reduce disease activity in people with MS. The Phase 2 study aims to enroll 180 adults, ages 18 to 55, with relapsing forms of MS who were diagnosed within the past two years. The experimental vaccine, called mRNA-1195, is designed to prevent EBV reactivation, which researchers hope could help reduce MS disease activity. The vaccine is being developed by Moderna.
The vaccine uses mRNA technology – the same platform used for Moderna’s COVID-19 vaccine. Instead of delivering a piece of the virus, mRNA vaccines provide instructions that the body’s cells use to make a small viral protein, training the immune system to recognize the virus and triggering a response similar to traditional vaccines.
Separately, researchers at the University of Basel published findings in 2024 in the journal Science suggesting that inhibition of a specific metabolic pathway in infected cells can diminish latent infection and therefore the risk of downstream disease. The team found that EBV triggers infected B cells to ramp up production of an enzyme called IDO1, which fuels the energy the virus needs to stay active and proliferate inside cells. Blocking that enzyme in mouse studies reduced viral load and tumor development. It points toward a potential antiviral approach, essentially starving the virus of what it needs to stay active inside cells.
A broader 2025 review of EBV vaccine platforms, published in Viruses, noted that researchers have summarized recent advances in various EBV vaccine platforms, including subunit, viral vector-based, nanoparticle-based, and mRNA vaccines, though no effective EBV vaccine has been approved for clinical use as yet. The field is moving faster than it ever has, driven largely by the MS connection.
What This Means for You
Start with context, not panic. The vast majority of people infected with EBV, which is nearly all of us, will not develop MS or an EBV-related cancer. The virus is a risk factor, not a sentence. But that doesn’t mean the information is irrelevant.
If you or your child had a confirmed case of mono, that’s worth keeping in your medical history. Screening or testing for past EBV infections can help identify people at a higher risk of developing nasopharyngeal cancer. Along with having a history of EBV, a person’s genes and lifestyle behaviors can increase risk. A conversation with your doctor about your personal risk factors, particularly if you have a family history of MS or certain cancers, is a reasonable and sensible step. You don’t need to walk in alarmed. Walk in informed.
For parents wondering about their kids: the risk of both mononucleosis and MS increases when primary EBV infection occurs after the age of 10, which is one reason some researchers have long advocated for vaccination programs targeting adolescents before their first exposure. An approved EBV vaccine doesn’t exist yet, but clinical trials are actively underway and moving at a pace the field has never seen before.
EBV in itself is not sufficient to trigger MS. Other unknown factors certainly play a role. That’s the science being honest about what it doesn’t yet know, which is exactly what good science does. What it does know, firmly and with growing certainty, is that a virus most of us have never thought twice about is worth paying attention to. The research is no longer preliminary. The question of what to do with it is just getting started.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.