Now that flu season is upon us, we are getting a lot of questions about the relationship between MS and infections, including influenza. MS does not impair the ability to fight off infections. Likewise, most of the treatments for MS do not impair the ability to fight infections, though there are a few exceptions to this. Most people with MS will therefore not be at any higher risk of colds or flu than the general population. However, infections may affect the MS. People with MS have an increased risk of having an MS attack at the time of infections, including colds, flu, pneumonia, bladder infections, etc. Some have estimated that about 1 out of 10 infections will be accompanied by an MS attack. Likewise, for every MS attack about 1 in 10 will be preceded by an infection. This means that about 90% of MS attacks occur in the absence of an infection.
Another important question is the role of vaccination in MS. In general, vaccinations do not seem to cause MS attacks. Because the vaccinations do not usually cause MS attacks, but the flu can cause an MS attack about 1 in 10 times, most neurologists recommend that MS patients receive the influenza vaccine. It is important to discuss with your doctor whether vaccination is right for you. More information is available here.