The CDC is warning parents to be vigilant for respiratory syncytial virus (RSV) if their children exhibit cold or flu symptoms.

[RSV] is actually the most common cause of bronchiolitis and pneumonia in children younger than 1 and in older adults over age 65.

“Almost everyone gets RSV by the time they are 2 years old,” according to the agency. “Healthy people usually experience mild, cold-like symptoms and recover on their own within a week or two.”

But those at higher risk of infection — people with asthma, people with congestive heart failure, infants, older adults and adults with chronic medical conditions — can develop serious complications through RSV.