“In fact, symptoms for most people are quite mild,” says Dr. Sandro Galea, MD, a physician and dean of Boston University School of Public Health. He says that up to 80% of people who contract the virus have only weak symptoms — such as a low-grade fever or cough — and that they may have mistakenly attributed these to the common cold or some other minor ailment. “It’s definitely possible to have it and not realize it,” he says.