Clearly self-isolation to prevent yourself being exposed to people who may be carrying and shedding the virus is an important public health measure. This is being implemented in some countries in an attempt to flatten the peak of the COVID-19 epidemic. The UK is one such country that is recommending certain vulnerable groups self-isolate; the list below includes people with MS. Clearly you have to follow national, regional and local guidelines and these may change quite rapidly; for example, we are expecting London to go into lock-down in the next day or two.
However, I don't think all pwMS are vulnerable. I think this advice is referring to patients who are severely immunosuppressed, i.e. those who have been treated with specific immune reconstitution therapies (HSCT, alemtuzumab and possibly cladribine) in the last 3-6 months. I say 3-6 months because post IRTs you immune system recovers at different rates and this advice probably refers to patients who still have very low lymphocyte counts, i.e. less than 500/mm3.
I personally don't think this advice refers to patients on other DMTs, which may be immunomodulatory or less immunosuppressive.
Another group this advice refers to is those with advanced MS with swallowing and breathing difficulties. These types of patients will be more vulnerable to secondary lung complications if they did get COVID-19.
Date & Disclaimer: 19-March-2020; please note this information will be time limited and will change as new data emerges.