Every year, two million children die of acute respiratory infections. Among the culprits are several different viruses, one of which your child almost certainly has had without you or the doctors ever knowing it.

The good news is that researchers believe you are most likely immune after having had this virus just once.

The human metapneumovirus (hMPV) often appears disguised as a cold. Part of the reason it has stayed hidden from doctors is that it was only discovered in 2001. A team of Dutch virus researchers had the thrill of a lifetime when they realized that they had discovered a new virus. Their joy certainly wasn’t lessened by the fact that the virus they discovered turned out to be one of the most common viruses in children who are hospitalized due to respiratory complications.

According to the World Health Organization, two million children die annually from acute respiratory infections. Even though the hMPV virus has been able to hide from researchers for a long time, it is not necessarily something you want to experience. Most people will have symptoms similar to a cold, but for some, the virus causes the respiratory system to swell and clog with mucus.