re: Eat the hell out of probiotics and take fricktons of Vitamin C

Limited by extrapolating from flu data

https://examine.com/topics/coronavirus/

Supplementation

Nobody knows how well cold/flu supplement trials apply to coronaviruses. The novel coronavirus is too new and is not structurally the same as either influenza or the various cold viruses.

For prevention, focus on handwashing and the like. If you feel sick, follow your doctor’s advice. That being said, there are a few supplements that people commonly ask us about for cold and flu. The below information may be handy to know, given that most people who feel sick at the moment (early March 2020) will have cold or flu, not COVID-19. Do not rely on supplements if you suspect COVID-19. See a physician and get real medical care. This page contains a more fleshed-out evidence breakdown, but in short, the cold/flu supplements are:

Moderate evidence for cold or flu:

Vitamin C can reduce the duration of cold symptoms if you’ve started taking it regularly before falling sick. This seems especially true for athletes and older people.[28][29][30][31]

Vitamin D can help prevent upper respiratory infections.[32][33][34][35] People’s spending a lot of time indoors in the winter is tied to seasonal flu through higher viral transmission in closed areas and a lack of sun (in addition to allowing your skin to synthesize vitamin D, solar UV rays can inactivate viruses).[36][37]

Zinc oral lozenges can reduce symptom severity, due to inhibiting viral replication at the back of your throat.[38][39][40] Swallowed tablets aren’t effective, and nasal spray may cause permanent adverse effects.[41] Zinc acetate lozenges may be a bit more effective than zinc gluconate lozenges, although perhaps not significantly so.[40][42]

Weak or preliminary evidence for cold or flu:

Garlic has many more antibacterial studies than antiviral studies.[43][44] Limited evidence exists for the prevention (but not the treatment) of the common cold.[45]

Echinacea has some evidence, although the benefit shown is very small.[46][47]

Elderberry has some evidence, but very few studies exist thus far.[48][49]

Pelargonium sidoides also has few studies, and only on treatment, not on prevention.[50][51]

Probiotics aren’t one monolothic thing. Certain specific strains may help with prevention, although evidence is mixed, and efficacy may vary greatly by person due to everyone having a different gut microbiome.[52][53][54][55]

N-Acetylcysteine (NAC) has limited evidence for reducing flu episodes,[56] and a combination of L-cystine and L-theanine has limited evidence for reducing episodes of the common cold.[57] Note that NAC has evidence for tumor initiation in animals when used regularly at high doses.[58][59][60] Supplements aren’t automatically safe just because they’re available without a prescription. Buyer beware!