Updated: Feb 28, 2020
You would have to live in a cave to miss the thousands of photos of people donning masks in an effort to prevent contraction of coronavirus. While masks may help a little, what we really need is our immune systems optimized and a good antiviral agent. Unfortunately, at this point we don't have any good antivirals for the common cold, let alone the coronavirus.
However, I just read a review article from Frontiers in Microbiology (see article here) that summarizes much of the credible research out there on the antiviral properties of mushrooms. While we don't know all of the different combinations of compounds that have antiviral activity, it appears that many of the time-honored medicinal mushrooms lead the pack as far as antiviral activity is concerned. So much more research needs to be done, but with a looming epidemic, I'm going with the research thus far. One of the most studied is good ole Turkey Tail (Phylum Basidiomycota; fungal order Polyporales) which grows in the woods that surround my house and farm. I found more than 30 studies on its antiviral activities (see the article referenced previously plus this more recent article on Dengue and so many others!). However, since the current coronavirus outbreak is related to a "new" or novel virus, no specific studies have been published exploring the effectiveness of mushrooms on this virus. Nevertheless, even though the FDA has not specifically evaluated the antiviral properties of mushrooms (gotta make that disclaimer!), there's more data on mushrooms than the effectiveness of wearing masks. I'm going with the bulk of data which demonstrates antiviral and immune enhancing properties of mushrooms.
Unfortunately Turkey Tail is not a culinary mushroom, so don't try to eat it if you find it in your yard (I wouldn't recommend eating any foraged mushrooms in any case unless you're an expert or know someone who is). The medicinal compounds in mushrooms need to be carefully extracted from fruiting bodies of the mushroom which is another reason that you should source from a place that is reputable. The problem is that much of what passes for medicinal mushroom extract in the USA is bordering on worthless. Many sources in the States are filled with grain starches and/or are ground up mycelia (the mushroom's "roots") which have little medicinal value. Other products have not been extracted properly and therefore also border on worthless. This may sound a little scary, but the best sources of medicinal mushrooms that I know of are from China. Mushroom farmers have grown medicinal mushrooms there for thousands of years and most farms are far, far away from the industrial centers and large cities where all the pollution and disease is centered (I have a Chinese friend who has 4 brothers/sisters because the farmers are so remote that the government doesn't/can't enforce the one child policy where they live).
Even if we never have to confront the reality of the current coronavirus in our country, state, or city--I'm still going to use quality mushroom extracts for my health. Again, there's no FDA backing on this, but there's plenty of research published on the immune-enhancing and even cancer-fighting properties of quality mushroom extracts (note emphasis on quality! Reference here).
What have I got to lose? Except maybe coronavirus or cancer...