The Centers for Disease Control and Prevention is warning about the spread of a common childhood virus that can cause muscle weakness or paralysis in rare cases.

The CDC issued an alert Friday about enterovirus D68, which most commonly leads to respiratory illness among kids, with symptoms that are often mild but can become severe. The enterovirus family is large, and polio falls within it; both EV-D68 and poliovirus can invade the nervous system and cause muscle weakness.

Occasionally, EV-D68 can result in a condition called acute flaccid myelitis, or AFM, which is characterized by inflammation in the neck region of the spinal cord. Some people who experience AFM have difficulty moving their arms, while others experience weakness in all four extremities. During a large outbreak in the U.S. in 2014, around 10% of people with EV-D68 went on to develop AFM.

Full recovery from AFM is rare, and although most patients improve to some extent, the process is often difficult, and it requires rehabilitation.