In an abstract published in October, 2020, fluvoxamine showed promise in a randomized, placebo-controlled trial of 152 COVID-19 positive outpatients:
152 participants were randomized in the modified intention to treat group. No patients (0/80, 0%) in the fluvoxamine group clinically deteriorated, compared to 8.3% (6/72) in the placebo group (logrank chi-square 6.8, p=0.009).
Fluoxetine has also shown anti-SARS-CoV-2 activity in vitro in Vero and Calu-3 cells.
Mechanism of possible benefit?
Mechanisms of potential benefit in COVID-19 may include sigma-1 receptor agonism. See "Fluvoxamine alleviates ER stress via induction of Sigma-1 receptor" and "Modulation of the sigma-1 receptor–IRE1 pathway is beneficial in preclinical models of inflammation and sepsis".
An observational study of 7,345 hospitalized COVID-19 patients hinted at possible benefit of prior SSRI usage.
As an anti-viral
In an October, 2020 preprint, fluoxetine showed in vitro anti-SARS-CoV-2 activity in Vero and Calu-3 cells.