A future mono vaccine may have a shot at defeating multiple sclerosis, a new study suggests

• A study provides the strongest evidence to date suggesting the Epstein-Barr virus may lead to multiple sclerosis.
• Scientists disagree about whether EBV definitively causes MS.

Scientists have found the strongest evidence to date that an infection from the Epstein-Barr virus could significantly increase the risk of developing multiple sclerosis, a degenerative disease, new research suggests.

"Our data strongly suggest EBV is the leading cause of MS," Dr. Kjetil Bjornevik, a research scientist at Harvard T.H. Chan School of Public Health and lead author of the study, which was published in the journal Science on Thursday, told STAT News.

The findings offer hope that a vaccine or early treatment of the virus could one day help prevent multiple sclerosis, Alberto Ascherio, an author of the study and epidemiology professor at the Harvard T.H. Chan School of Public Health, told Insider.

But experts unaffiliated with the study say there's still uncertainty about whether the virus causes MS.

The study suggests a much higher MS risk after infection

Multiple sclerosis, a progressive disease that affects the brain and spinal cord, is caused by inflammation that attacks myelin, the fatty tissue surrounding the nerves, according to the National Institutes of Health. In 2020, there were 2.8 million people living with multiple sclerosis worldwide.

When myelin degrades, it's more difficult for the nerves to send messages to the brain, causing blurred vision, weak limbs, tingling sensations, unsteadiness, and fatigue, according to the Multiple Sclerosis International Federation. In advanced cases, patients can have muscle weakness in their arms and legs, making it difficult to walk or stand.

To determine the link between an EBV infection and MS, scientists analyzed samples from the Department of Defense Serum Repository, a collection of more than 60 million blood samples taken from more than 10 million active and reserve duty members every few years.

The scientists compared blood samples of 1,566 service members who didn't develop MS to samples from 801 service members who received an MS diagnosis during the course of the study. Of those individuals, 107 members of the control group and 35 members of the group that subsequently developed MS started off without an EBV infection.

By the end of the study, 34 of the 35 people who developed MS had been infected with EBV at some point during the study. In these cases, the infection always preceded the diagnosis.

In other words, all but one person in the study who developed MS had a previous EBV infection — and having that infection increased the likelihood of getting MS later in life by 32-fold in the study, the scientists found.

Jury's still out on whether EBV definitively causes MS, some experts say

It's difficult to definitively prove that EBV, which is also the virus behind mononucleosis, causes MS.

Although it's the most authoritative study to date, the way the study is designed means scientists can't know with absolute certainty that the virus causes the disease, Alan Thompson, dean of the Faculty of Brain Sciences from University College London and a peer reviewer on the new paper, told Insider.

It's possible that the virus does cause the disease, Thompson added, scientists just aren't 100% sure.

"We do need to be a little cautious about getting too excited," Catherine Godbold, research communications manager for the MS Society, a charity in the UK, said of the study results.

The gold standard would be to do a randomized controlled trial, but that's impractical as well as unethical, Godbold explained, because it would involve infecting half of study participants with EBV. The current study design is the next best thing, she added.

While the study did not directly investigate how EBV could potentially cause multiple sclerosis, previous research may provide clues.

Some research groups have suggested that the virus carried a molecule at its surface that looks like myelin, confusing immune system, which sees it as a foreign invader to attack, causing inflammation, according to STAT News. Different researchers theorize that immune cells, called B cells, may turn against the body when infected by EBV, STAT reported.

A vaccine offers hope, but may take decades

While there's currently no treatment or vaccine against EBV, the pharmaceutical company Moderna is in the early stages of developing an EBV vaccine, using similar technology to current mRNA COVID-19 vaccines.

Using existing technology may quicken the availability of EBV vaccines, by shortening the timeline from decades to years, Thompson said.

Most people catch EBV during their lifetimes, usually during childhood, but the vast majority don't develop multiple sclerosis, so it's also important to figure out what other factors are at play. Genetics, vitamin D deficiency, and childhood obesity are all risk factors associated with multiple sclerosis.

Aschiero is hopeful: "If you could prevent infection, we should be able to prevent the large majority of MS cases."