Hydroxychloroquine is a zinc ionophore. It provides an ion channel that permits zinc to enter the cell and inhibit viral replication. In order to be effective, the zinc + ionophore antiviral should be administered early. Hospitalized ICU patients on ventilators are far from ideal candidates. Chinese (successful) studies used Zinc and Hydroxychloroquine; never Hydroxychloroquine without zinc.

Improving the efficacy of Chloroquine and Hydroxychloroquine against SARS-CoV-2 may require Zinc additives - A better synergy for future COVID-19 clinical trials https://digitalcommons.mtu.edu/michigantech-p/1795/

Zn2+ Inhibits Coronavirus and Arterivirus RNA Polymerase Activity In Vitro and Zinc Ionophores Block the Replication of These Viruses in Cell Culture https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2973827/

Does Zinc Supplementation Enhance the Clinical Efficacy of Chloroquine/Hydroxychloroquine to Win Todays Battle Against COVID-19? https://www.preprints.org/manuscript/202004.0124/v1]

https://en.wikipedia.org/wiki/Ionophore Zinc ionophores have been shown to inhibit replication of various viruses in vitro:

Coxsackievirus

Equine viral arteritis

Hepatitis C virus

Herpes simplex virus

Human coronavirus

Human Immunodeficiency Virus

Mengovirus

MERS coronavirus

Rhinovirus

SARS coronavirus

Zika virus