I never knew what Quercetin and Pterostilbene were until COVID came along. Since discovering, we have added it to our arsenal of supplement we had read would help fight viruses. It works amazing when it comes to fighting off sickness and improving overall health. Mixed with Zinc and Vitamin D and C, it’s a powerful antivirus that will help prevent kill and prevent viruses. At a minimum, it will definitely shorten duration of being sick from what we have found personally. I can’t recommend this enough.