I've written a number of articles discussing a variety of natural supplements known to inactivate viruses, quell inflammation and regulate the inflammatory process. Examples include vitamin C, melatonin and licorice root. You can find them all on my Coronavirus Resource Page.

Blocking Cytokine Storm Is Crucial

Most recently, the paper1 "COVID-19: Potential of Microalgae Derived Natural Astaxanthin as Adjunctive Supplement in Alleviating Cytokine Storm," published April 21, 2020, on the research library website SSRN, addresses the use of astaxanthin, a potent antioxidant supplement derived from microalgae. According to the authors:

"There is rationale, pre-clinical evidences of effectiveness and evidence of safety from long-time use for other indications to justify possible inclusion of natural astaxanthin as adjunctive in combination with primary anti-viral drugs therapy will hugely benefit COVID-19 patients by improving their health and reducing recovery time …

Clinically, natural astaxanthin has shown diverse benefits with excellent safety and reported to block oxidative DNA damage, lowered C-reactive protein (CRP) and other inflammation biomarkers. Previous studies reported that natural astaxanthin exert positive effects in alleviating cytokine storm, acute lung injury, acute respiratory syndrome, etc …

Current understandings based on accumulated evidences suggest that SARS-CoV-2 induces a potential amplified inflammatory response to sequential consequences of ALI [acute lung injury], ARDS [acute respiratory distress syndrome] to a life-threatening dire consequence of potential septic shock with elevated expression of inflammatory related genes along with inevitable secondary infections, rather than increased viral load …

The attenuation of the cytokine storm by targeting key steps in the process may deliver improved outcomes … Shi et al. suggested a two-phase approach for potential treatments of COVID-19 patients: the first immune defense-based protective phase for non-severe COVID-19 cases and the second, inflammation-driven damaging phase for severe COVID-19 patients.

Zhang et al. presented a critical review … stating that blocking the cytokine storm at right time followed by initiation of anti-inflammation therapy is very critical for reducing the rate of fatalities. … A range of antioxidants as supplements will offer a window of quick recovery of patients by reducing post treatment side-effects."