New relapse of multiple sclerosis and neuromyelitis optica as a potential adverse event of AstraZeneca AZD1222 vaccination for COVID-19

•Vaccination to prevent severe cases of COVID-19 is key to controlling the pandemic.•Some vaccines may trigger rare autoimmune adverse events.•AZD1222 is here reported to trigger relapses of MS and NMOSD. We report on nine patients (eight cases of MS and one case of NMOSD) who presented a disease relapse in close temporal association with their first AZD1222 vaccination dose against COVID-19. These patients had been stable for a median period of six years, with no evidence of disease activity and no change in their medication. After a median of 13 days (7 to 25 days) from vaccination, they developed a new relapse with increased disability and new lesions on magnetic resonance imaging. Although this association may be rare, it might be an adverse event of AZD1222.