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Article History

Received: 14 December 2025

Revised: 20 March 2026

Accepted: 20 April 2026

First Online: 4 May 2026

Declarations

:

: The study adheres to the Declaration of Helsinki and its later amendments. Ethical approval for the MLC-R registry study was granted on 23 August 2021 by the Ethics Committee of the Technical University of Munich (TUM) (511/21). The data analysis received separate ethical approval from the Ethics Committee of the TUM on 5 September 2025 (2025–465-S-SB).

: Written informed consent was obtained from all subjects (or their legal guardian) involved in the study.

: Written informed consent was obtained from all subjects (or their legal guardians) involved in the study.

: All authors have completed the ICMJE uniform disclosure form. U.B. reports research funding from the Bavarian State Ministry of Health and Care, the Bavarian State Ministry of Science and Art, the German Center for Infection Research (DZIF), the Federal Ministry of Research, Technology and Space, the Federal Ministry of Health, and the Federal Joint Committee. CS received grants from the Federal Ministry of Health, consulting fees from Celltrend, and payment or honoraria from Bayer, Fresenius, Roche, Celltrend, Hausärzteverband Berlin, AGBAN AKADEMIE, and Berufsverband Dt. Internisten. Further, CS is a participant in advisory boards at Berlin cures and the Federal Institute for Drugs and Medical Devices (BfArM). M.A. received financial compensation from BioNTech and Pfizer for participating in advisory board meetings on Long COVID. C.C. received personal payment from the Austrian Chamber of Pharmacists for delivering vaccination training lectures. Q.D. and LC.P. report an MD scholarship from the German Center for Infection Research. LC.P. received a travel scholarship from the Lost Voices Foundation to attend the 2023 IACFS/ME Research and Clinical Conference. N.T. serves as Vice President of the German Society of Pediatric Infectious Diseases (DGPI). U.B. and C.S. are members of the medical advisory board of the German association for ME/CFS. All other authors declare no competing interests.