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Article History

Received: 1 September 2025

Accepted: 16 January 2026

First Online: 14 February 2026

Declarations

:

: Erwin De Cock and Jyothi Menon were employees of Syneos Health at the time of the study; they are no longer affiliated. Peter Oliver-Smith, Carlos Acosta, and Rona Esquejo-Leon are current employees of Biogen and may hold stock/options. Khalil Jomaa is a former Biogen employee and may hold stock/options.

: Regulatory classification and ethics approvals varied by country. In France, the study was classified as Recherche Non Impliquant la Personne Humaine (RNIPH [Research Not Involving Human Subjects]), declared to the Commission Nationale de l’Informatique et des Libertés (CNIL) and registered to the Health Data Hub on 8 December 2022 (registration no. F20221208091708). In Spain, the Instituto de Investigación Biomédica de Girona Josep Trueta (IDIBGI) determined that the study did not meet the definition of a prospective observational drug study and that no ethics submission was required. In the UK, the study was classified as a non-Clinical Trial of an Investigational Medicinal Product (non-CTIMP) and received a favorable opinion from the London-Brent Research Ethics Committee, with approval from the Health Research Authority and Health and Care Research Wales (IRAS Project ID: 318021; REC reference: 23/PR/0266). The T&M study was conducted in compliance with the approved protocol, the applicable principles outlined in Good Pharmacoepidemiology Practice guidelines, and the Declaration of Helsinki (1964 and its later amendments). Any adverse events associated with natalizumab were to be reported via normal reporting processes for a marketed product in compliance with applicable regulatory requirements. As for any observational study, the decision to treat a patient with natalizumab IV or SC was taken as part of routine care and was independent of this study. No patient personally identifiable information was collected; hence, no informed consent was required from patients. However, patients were informed via an Information Leaflet of the study and its purpose and asked for their verbal agreement (or refusal) for their natalizumab administration process to be observed.