Supplemental material, sj-jpg-2-cep-10.1177_03331024231198792 for Effect of COVID vaccination on monthly migraine days: a longitudinal cohort study by Britt W. H. van der Arend, Mirthe M. Bloemhof, Alle G. van der Schoor, Erik W. van Zwet PhD, Gisela M. Terwindt in Cephalalgi