Individuals having never been infected by the Epstein–Barr virus are at a reduced risk of getting MS, whereas those infected as young adults are at a greater risk than those having had it at a younger age.
Persoanele care nu au suferit niciodată de o infecție cu virusul Epstein-Barr sunt expuse unui risc redus de a contracta SM, în timp ce persoanele infectate ca adulți tineri sunt expuse unui risc mai mare decât persoanele expuse la vârste mai mici.