Key Inclusion Criteria:  Be enrolled in MS PATHS under Study 888MS001. Completed one or more COVID-19 questionnaire at a participating MS PATHS institution. Permission for data linkage either obtained when completing a local COVID-19 questionnaire or granted by waiver of informed consent from the local institutional review board (IRB) or ethics committee (EC).  Key Exclusion Criteria:  1. Other unspecified reasons that, in the opinion of the Investigator or Biogen, make the participant unsuitable for participation in the sub-study. A participant only needs to complete the assessments deemed necessary by the Investigator.  Note: Other protocol defined Inclusion/Exclusion criteria may apply.