You've probably heard about respiratory viruses like RSV and the flu, but now doctors are saying a new virus is on the rise. Cases of human metapneumovirus, or HMPV, spiked this spring, according to the CDC. The virus causes many of the same symptoms as the flu , including coughing, runny nose, sore throat, and fever. Older people and young children are most vulnerable, and many don't know they have it until they are tested at a hospital.