Viral infection , injury, and pregnancy are the most frequently proposed triggers for multiple sclerosis (MS). But there is no scientific proof that they trigger MS in a person who does not already have the disease.

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.

Studies have also shown that women with MS have:¹

• Fewer relapses than expected while they are pregnant, especially during the third trimester (last 3 months of pregnancy).
• More relapses than expected during the first few months after giving birth.

In people who have been diagnosed with MS, there is no proof that attacks or worsening of the disease is brought on by:

• Insertion of hypodermic needles into the fluid surrounding the lower spine (lumbar puncture).
• Surgery and anesthesia.
• Emotional stress.