Seropositivity towards rubella virus (RV) increases the risk of developing multiple sclerosis (MS), according to new research. The case–control, Swedish biobank study analysed seropositivity towards RV in vaccinated and unvaccinated individuals before the clinical onset of MS. The results showed that people with MS had higher seroreactivity to RV than people without MS. Moreover, RV seropositivity was associated with a higher risk of developing MS in unvaccinated individuals. The finding adds to growing evidence for viral triggers of MS beyond the Epstein–Barr virus.