SARS-CoV-2 has several biological properties that could plausibly trigger or unmask multiple sclerosis, but definitive proof that COVID-19 causes new MS in otherwise healthy people does not yet exist. The concern is grounded in real science: the virus can breach the blood-brain barrier, its proteins share structural similarities with human myelin components, and clinicians have reported new MS diagnoses appearing weeks after infection. What remains unclear is whether these cases represent true viral triggering of an autoimmune cascade or the unmasking of a disease that was already silently developing.
Viruses and MS Have a Long History
The idea that a virus could set off multiple sclerosis is not new to the COVID era. For decades, researchers have explored how viral infections might spark the immune system to mistakenly attack myelin, the insulating sheath around nerve fibers in the brain and spinal cord. Multiple mechanisms have been proposed, including situations where virus-fighting immune cells accidentally cross-react with myelin because pieces of the virus look like pieces of myelin, and scenarios where the inflammatory cleanup after a viral infection causes collateral damage to nearby nerve tissue.1Europe PMC. Virus-Induced Demyelination: The Case for Virus(es) in Multiple Sclerosis
The strongest precedent comes from Epstein-Barr virus. Epidemiological evidence now identifies EBV as essentially a prerequisite for developing MS, though the exact way it contributes to the disease remains an open question.2PubMed Central. Epstein-Barr Virus in Multiple Sclerosis: Past, Present, and Future A study of patients in Sri Lanka found that those with high EBV antibody levels had roughly an 11-fold higher risk of MS compared to those with low levels, reinforcing a dose-response relationship between the intensity of a person’s immune reaction to EBV and their MS risk.3PubMed. Epstein-Barr virus seropositivity in a cohort of Sri Lankan patients with early multiple sclerosis This backdrop matters because it establishes that viral infections genuinely can play a role in MS. The question with COVID-19 is whether a different virus, operating through overlapping or distinct mechanisms, could do something similar.
How SARS-CoV-2 Gets Into the Brain
For a virus to trigger damage to the central nervous system, it needs a way in. SARS-CoV-2 appears to have several. Research has identified at least two main routes: the virus can infect the cells lining blood vessels in the brain, effectively hitchhiking through the blood-brain barrier, or it can use immune cells as carriers that slip past the barrier like Trojan horses. Studies have found viral particles in brain capillary cells, suggesting the blood-borne route is the most likely path.4PubMed Central. Exploring SARS-CoV-2 impact on blood-brain barrier and its composition: A review
Beyond just crossing the barrier, SARS-CoV-2 appears to damage it. Research indicates the virus ramps up production of an enzyme that breaks down structural proteins in the barrier’s basement membrane and triggers changes in cell shape that loosen the barrier’s integrity.5PubMed Central. Alteration of the blood-brain barrier by COVID-19 and its implication in the permeation of drugs into the brain Imaging studies of people with long COVID and brain fog have revealed measurably increased leakiness in their blood-brain barriers, particularly in the temporal and frontal lobes, even when standard MRI scans looked normal.6Nature Neuroscience. Blood–brain barrier disruption and sustained systemic inflammation in individuals with long COVID-associated cognitive impairment A leaky blood-brain barrier could let immune cells and inflammatory molecules flood into the central nervous system more easily, setting the stage for the kind of immune attack that characterizes MS.
Molecular Mimicry Between the Virus and Myelin
Perhaps the most compelling mechanistic link between SARS-CoV-2 and MS involves molecular mimicry, where pieces of the virus’s proteins structurally resemble pieces of human proteins closely enough that immune cells trained to fight the virus accidentally attack the body’s own tissue. Studies using computational approaches have found that the degree of mimicry between SARS-CoV-2 and human proteins is far greater than what you would expect by chance alone.7PubMed Central. Evidence for Molecular Mimicry between SARS-CoV-2 and Human Antigens: Implications for Autoimmunity in COVID-19
When researchers looked specifically at nerve-related proteins, they found that the virus’s spike protein shares structural segments with myelin-associated glycoprotein, a component of the protective coating around nerves.8Computational and Structural Biotechnology Journal. Molecular Mimicry of SARS-CoV-2 Spike Protein in the Nervous System: A Bioinformatics Approach Another study zeroed in on a different viral protein, the nucleocapsid, and found it shared significant structural overlap with 22 proteins already linked to MS. One of these was proteolipid protein (PLP), a canonical MS-associated protein and major component of myelin in the central nervous system.9Scientific Reports. Sequence similarity between SARS-CoV-2 nucleocapsid and multiple sclerosis-associated proteins provides insight into viral neuropathogenesis following infection
These structural similarities do not by themselves prove that COVID-19 causes MS. Molecular mimicry is a necessary ingredient but not a sufficient one: plenty of viruses share protein fragments with human tissues without triggering autoimmune disease in most people. What makes the finding notable is that the overlap involves proteins already implicated in MS, not random human proteins. Combined with the virus’s ability to enter the brain and activate resident immune cells called microglia, the pieces fit a plausible autoimmune cascade involving mimicry, bystander activation, and the spread of immune targeting from one myelin protein to others.10PubMed. COVID-19 as a Trigger of Brain Autoimmunity
Case Reports of New MS After COVID-19
Clinicians have documented individual cases of patients who developed MS shortly after recovering from COVID-19. One early report described a patient who sought care for worsening vision after a COVID-19 infection; imaging revealed inflammation of the optic nerve and demyelinating lesions scattered through the central nervous system, consistent with MS.11PubMed Central. Multiple sclerosis following SARS-CoV-2 infection In another case, a 36-year-old man with no prior neurological history met the full diagnostic criteria for MS two months after a confirmed SARS-CoV-2 infection.12Neuroimmunology Reports. A case report of multiple sclerosis after COVID-19 infection: causality or coincidence?
These reports are striking, but case reports carry inherent limitations. MS typically develops over years of subclinical activity before a person notices anything wrong. It is entirely possible that these patients had early, undetected MS that was pushed into its first noticeable flare by the systemic inflammation of a COVID-19 infection, rather than being caused from scratch by the virus. In one study of patients who developed demyelinating disease shortly after COVID vaccination, MRI and other testing showed evidence of preexisting subclinical central nervous system disease, suggesting the immune trigger had unmasked something already underway rather than creating something new.13PubMed Central. Clinical onset of CNS demyelinating disease after COVID-19 vaccination: denovo disease? The same unmasking dynamic could apply to infection-triggered cases. Large population-based studies tracking MS incidence rates before and after the pandemic are still needed to determine whether COVID-19 is actually causing more people to develop MS or simply accelerating the timeline in those who were already on their way.
What Happens When People With MS Get COVID
For the millions of people already living with MS, the more immediate concern has been whether catching COVID-19 could trigger a relapse. The answer appears to be yes, at least for some. A systematic review and meta-analysis pooling data across multiple studies found that roughly 7% of MS patients experienced a relapse after COVID-19 infection, though individual studies reported rates ranging from 2% to 20%.14PubMed Central. Incidence of multiple sclerosis (MS) relapse after COVID-19 infection: A systematic review and meta-analysis One case report documented a 27-year-old woman with relapsing-remitting MS who experienced a new exacerbation just two weeks after a mild bout of COVID-19, despite being on disease-modifying therapy at the time.15PubMed Central. SARS-CoV-2 triggered relapse of multiple sclerosis
That 7% pooled relapse rate, while not trivial, needs context. MS relapses can be triggered by many infections, not just COVID-19. Urinary tract infections, the flu, and other common illnesses have long been recognized as relapse triggers. So while COVID-19 clearly belongs on the list of infections that can destabilize MS, the evidence does not single it out as uniquely dangerous compared to other systemic infections. The more relevant risk factors appear to be disability level and the type of medication a person is taking, as discussed below.
MS Medications and COVID-19 Risk
Some of the most effective MS treatments work by depleting B cells, a type of immune cell that produces antibodies. Rituximab and similar drugs are widely used in MS because they powerfully suppress the overactive immune responses that drive the disease. The trade-off became painfully apparent during the pandemic: these same drugs blunt the body’s ability to mount a proper antibody response to both the virus and the vaccine.
In one study of nearly 4,000 vaccinated MS patients, those on rituximab were about seven times more likely to be hospitalized with COVID-19 than MS patients on other treatments or no treatment at all. However, no rituximab-treated patients in the study died. Receiving an mRNA vaccine and getting a booster dose each independently reduced hospitalization risk, and timing the vaccine at least six months after the last rituximab infusion cut the odds of hospitalization by about 78%.16JAMA Network Open. Analysis of Rituximab Use, Time Between Rituximab and SARS-CoV-2 Vaccination, and COVID-19 Hospitalization or Death in Patients With Multiple Sclerosis Another study found that while a large proportion of rituximab-treated patients had no detectable antibodies after two vaccine doses, hospitalization rates remained low overall, suggesting that vaccinated patients still benefit even without a measurable antibody response.17Multiple Sclerosis and Related Disorders. Hospitalisations and humoral COVID-19 vaccine response in vaccinated rituximab-treated multiple sclerosis patients
The explanation likely involves T cells. Research tracking long-term immune responses in MS patients on B-cell-depleting drugs found that while their antibody levels were consistently lower than those of untreated patients, their T-cell responses were actually higher. A booster dose significantly improved antibody levels even in B-cell-depleted patients, and actual COVID-19 infection further boosted immune responses.18PubMed Central. Long-Term Immune Response Profiles to SARS-CoV-2 Vaccination and Infection in People with Multiple Sclerosis on Anti-CD20 Therapy The practical takeaway for people on these treatments is that vaccination remains beneficial, and coordination between infusion timing and vaccine doses can meaningfully improve protection.
Not all MS drugs carry the same COVID-related concerns. A review of how different therapies interact with the immune response to COVID-19 found that most DMTs primarily affect the adaptive immune system while leaving the innate immune system largely intact, meaning the body’s first-line defenses against the virus remain functional. Interferon-beta and glatiramer acetate, two older MS treatments, were associated with the lowest infection risk. Some researchers have even speculated that certain DMTs could have a protective side effect by dampening the exaggerated inflammatory response that causes severe COVID-19 lung damage.19PubMed Central. Outcome of COVID-19 Infection in Patients With Multiple Sclerosis Who Received Disease-Modifying Therapies: A Systematic Review and Meta-Analysis Studies of children with MS have echoed these findings, reporting no increased COVID-19 risk in pediatric patients with lower disability scores who were not on B-cell-depleting drugs.20PubMed Central. The Outcome of COVID-19 in Pediatric-Onset Multiple Sclerosis Patients
COVID Vaccination and Demyelination Concerns
Early in the vaccine rollout, reports emerged of people developing demyelinating symptoms shortly after receiving a COVID-19 vaccine, raising understandable alarm. One case series described 18 patients with no prior COVID-19 infection who developed neurological symptoms including vertigo, optic nerve inflammation, and spinal cord inflammation within 14 days of receiving either a Pfizer or AstraZeneca vaccine.21PubMed Central. CNS Demyelination Syndromes Following COVID-19 Vaccination: A Case Series For people with existing MS, a systematic review of case reports concluded that vaccination could trigger relapses in some patients, but because the infection itself also triggers relapses, the benefit of vaccination outweighs the risk, and vaccination should be continued and encouraged in this population.22PubMed Central. Multiple sclerosis relapse after COVID-19 vaccination: A case report-based systematic review
The logic here is essentially a risk comparison. Both the virus and the vaccine expose the immune system to SARS-CoV-2 spike protein, which, as the mimicry research shows, shares structural features with myelin components. But an actual infection also breaches the blood-brain barrier, activates brain-resident immune cells, and produces a far broader and more intense inflammatory response than a vaccine does. Researchers investigating the post-vaccination cases found evidence that many of these patients had preexisting subclinical disease, suggesting the vaccine was unmasking rather than creating MS.13PubMed Central. Clinical onset of CNS demyelinating disease after COVID-19 vaccination: denovo disease? The consensus in the neurology community has remained that for people with MS or at risk of MS, infection poses a greater threat than vaccination.
Severe COVID-19 and Brain Injury Markers
One way researchers have tried to gauge how much brain damage COVID-19 causes is by measuring neurofilament light chain (NfL) in the blood, a protein released when nerve fibers are injured. In hospitalized COVID-19 patients, NfL levels were normal in those requiring only basic oxygen support but jumped dramatically in patients who needed mechanical ventilation in intensive care, where average levels reached roughly ten times higher. Higher NfL levels were strongly associated with worse outcomes.23PubMed Central. Serum neurofilament light chain in COVID-19 and the influence of renal function However, the same study found that declining kidney function, common in severe COVID-19, also drives NfL levels up, complicating interpretation. This matters because NfL is also used as a biomarker in MS to track disease activity and nerve damage. If someone who recently recovered from severe COVID-19 has elevated NfL, it could reflect direct nerve injury from the infection, kidney-related accumulation, or early signs of a demyelinating process, and distinguishing between these causes is not straightforward.
The Gut Microbiome Connection
A less obvious angle on both COVID-19 and MS involves the gut. The trillions of bacteria living in your intestines influence immune regulation throughout the body, including in the brain. A recent study transplanted gut bacteria from MS patients into mice and found that microbiota from people diagnosed more recently with MS induced severe autoimmune brain disease in the animals, while microbiota from long-term MS patients and healthy individuals caused only mild disease. The bacteria from early-stage MS patients were less effective at promoting regulatory T cells, the immune cells that normally keep inflammation in check, and more effective at stimulating inflammatory signals.24bioRxiv. Gut microbiome changes over the course of multiple sclerosis differentially influence autoimmune neuroinflammation
COVID-19 is known to disrupt the gut microbiome, sometimes persistently. If infection shifts gut bacteria toward a more inflammatory profile similar to what is seen in early MS, this could represent yet another pathway by which the virus nudges the immune system in a dangerous direction. This research is still early, conducted partly in animal models and not yet through peer review for the microbiome transplant work, but it opens a door that researchers are actively walking through. The gut-brain connection in MS is increasingly seen as a factor that could help explain why certain infections, environmental changes, or even dietary shifts correlate with disease onset or worsening.