Potential conflicts of interest . F. M. reports funding from the Nederlands Kenniscentrum Chronische Vermoeidheid (NKCV) Foundation. C. R. reports grants (paid to institution for the present study) from the EU Horizon 2020 Research and Innovation Framework Programme and the Michael J Fox Foundation, being a member of the Pandemic Preparedness Plan Committee of the Royal Netherlands Academy of Arts and Sciences, and being a member of the Long-term Effects of COVID-19 Committee of the Health Council of the Netherlands. H. K. reports funding for this study from the Netherlands Organization for Health Research and Development (ZonMw, project 10430012010025; paid to institution) and grants from ZonMw, the Dutch Cancer Society, MS research, and the NKCV Foundation. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.