Royal Oak Viral Infections: Viral Infections are any illness you get from a virus (a small germ that uses your cells to reproduce). Common viral illnesses include colds, the flu, COVID-19, norovirus (“stomach flu”), HPV (warts), and herpes simplex virus (cold sores). Cold Sores are a group of tiny, painful blisters caused by the herpes simplex virus (HSV). They’re also called fever blisters or herpes simplex labialis.