Vitamin C and quercetin have synergistic effects that make them useful in the prevention and early at-home treatment of COVID-19. Both are part of the MATH+ protocol developed by the Front Line COVID-19 Critical Care Working Group (FLCCC)
For COVID-19 prophylaxis, the FLCCC recommends vitamin C, quercetin, zinc, melatonin and vitamin D3
The at-home treatment for mildly symptomatic patients is very similar to the prophylactic regimen, but adds several optional drugs, including aspirin, famotidine (an antacid) and ivermectin (a heartworm medication that has been shown to inhibit SARS-CoV-2 replication in vitro)
The in-hospital MATH+ protocol calls for intravenous methylprednisone, high-dose ascorbic acid (vitamin C), thiamine and heparin. Optional additions include melatonin, zinc, vitamin D3, atorvastatin, famotidine and magnesium
There are two distinct phases or stages of COVID-19 — the viral replication stage and the immune dysfunction stage — and the treatment must be appropriate for the stage you’re in. Equally crucial is starting aggressive treatment as early as possible
Quercetin was initially found to provide broad-spectrum protection against SARS coronavirus in the aftermath of the SARS epidemic that broke out across 26 countries in 2003.1,2,3 Now, some doctors are advocating its use against SARS-CoV-2, in combination with vitamin C, noting that the two have synergistic effects.

Incidentally, ascorbic acid (vitamin C) and the bioflavonoid quercetin (originally labeled vitamin P) were both discovered by the same scientist — Nobel prize winner Albert Szent-Györgyi.4,5 Quercetin’s antiviral capacity has been attributed to five main mechanisms of action:

Inhibiting the virus’ ability to infect cells by transporting zinc across cellular membranes
Inhibiting replication of already infected cells
Reducing infected cells’ resistance to treatment with antiviral medication
Inhibiting platelet aggregation — and many COVID-19 patients suffer abnormal blood clotting
Promoting SIRT2, thereby inhibiting the NLRP3 inflammasome assembly involved with COVID-19 infection
Similarly, vitamin C at extremely high doses also acts as an antiviral drug, effectively inactivating viruses. During the 2003 SARS pandemic, a Finnish researcher called6 for an investigation into the use of vitamin C after research showed it not only protected broiler chicks against avian coronavirus, but also cut the duration and severity of common cold in humans and significantly lowered susceptibility to pneumonia.