In someone who already has MS, a viral infection such as the flu can trigger a relapse. There is no proof that flu vaccination (or any other vaccination) increases the chance of a relapse. In fact, people with MS may want to consider getting an annual flu shot to avoid infection and any attacks it may trigger. But there is no evidence that the nasal spray vaccine is safe for people with MS. If you have MS, talk with your doctor about whether a nasal spray vaccine is right for you.