Identification of exposure, other treatments and covariates and the matching procedure
Exposure/non-exposure to fluvoxamine was identified based on timing of prescriptions with the respective ATC code (N06AB08) relative to the index COVID-19 diagnosis. All other psychiatric and other treatments required for identification of patient subsets and covariate matching are listed in Appendix, Table A1. We implemented exact matching using package MatchIt 14 in R15. For all contrasts (Group A vs. B, A vs. C and B vs. C), patients were matched in respect to age, sex, vaccination status (type of vaccine and timing relative to the index COVID-19 episode), calendar period of COVID-19 diagnosis, and a range of comorbidities and pharmacological treatments (detailed in Table 2). For the Group A vs. Group B comparisons, additional matching included also psychiatric diagnoses (Table 2). Comparisons vs. Group C patients did not include these covariates, since Group C patients were free of psychiatric conditions (by definition). Identification of all comorbidities used for matching is detailed in Appendix, Table A2-Table A4, and section on immunocompromised and diabetic patients.