In multiple sclerosis (MS), the immune system attacks the central nervous system, damaging nerves and myelin, the insulating material that covers and protects nerve fibers. This damage affects how signals are relayed from the brain and spinal cord, which can cause fatigue, numbness, weakness, vision change, loss of balance, and even cognitive impairment. The course and severity of the disease are unpredictable and vary between individuals. Part of managing MS is getting vaccinations to prevent infections. In August 2019, the American Academy of Neurology issued a guideline on vaccines for people with MS and recommended that patients with MS get regular vaccinations, including an annual influenza shot. A flu shot is especially key during the coronavirus pandemic for several reasons. First, the flu kills thousands of people each year. Second, you risk contracting COVID-19 in the hospital if you are admitted for severe flu symptoms. Finally, contracting the flu and COVID-19 simultaneously may result in more severe illness and may lower your defenses in combatting the coronavirus. Experts recommend that people with MS, especially those who are on disease-modifying therapies, get the killed vaccine preparation of the flu shot and not the live weakened version. Although researchers have not found a link between live vaccine use and infection risk, they think using a live vaccine when you have a suppressed immune system may be risky.

In some instances, however, your doctor may advise against a vaccination if you had a past allergic reaction or some other adverse response to it. Some evidence also suggests that if you’re taking certain disease-modifying medications such as alemtuzumab (Lemtrada) and ocrelizumab (Ocrevus), flu shots may not fully protect against infection. In addition, several oral drugs, including fingolimod (Gilenya), siponimod (Mayzent), ozanimod (Zeposia), and cladribine (Mavenclad) have restrictions regarding vaccines both before and during treatment.

Sometimes vaccinations may lead to flare-ups of symptoms. These types of flare-ups are also known as pseudo-exacerbations, so called because the symptoms are due to a known external source, in this case the vaccine. The symptoms are real, but they are not caused by new disease activity. If you develop a fever after a flu shot, you could experience a pseudo-exacerbation, but once the fever is under control, the symptoms should abate. Even if the vaccine is only partially effective, which happens sometimes, and you do get the flu, the symptoms probably won’t be as severe as they might have been if you hadn’t been vaccinated.

Up until 16 years ago, some researchers thought the flu vaccine might trigger an immune response that could lead to neuroimmune disorders, including MS. Those concerns were put to rest by a 2004 review from a panel of experts at the Institute of Medicine, an independent nonprofit that provides unbiased and authoritative advice to policymakers and the public, that concluded that vaccines did not raise the risk. The review committee did recommend additional research to better understand how the flu develops and to anticipate which strains might be more neurologically active.

Before getting a flu shot or any other vaccine, talk to your doctor about what’s best for you. Most vaccinations are not emergencies, so waiting until an MS attack has passed before getting a vaccine may be safest. Also, certain disease-modifying therapies such as ocrelizumab, fingolimod, siponimod, ozanimod, cladribine, and alemtuzumab require specific waiting periods between vaccinations and starting therapy.