Children may have milder symptoms when infected with COVID-19, which could contribute to a greater spread of the virus so long as it goes undetected in younger people, new research suggests.

SARS-CoV-2, the virus that causes the disease COVID-19, has already infected millions of Americans across the country. President Trump outlined Monday new guidelines for Americans to follow over the next two weeks to combat the virus, including avoiding meeting in groups of more than 10 people and offering support to school closures.

“It’s important for the young and healthy people to understand that while they may experience milder symptoms, they can easily spread this virus, and they will spread it indeed, putting countless others in harm’s way. We especially worry about our senior citizens,” said Trump.

COVID-19 is reported in nearly every country of the world, and in every US state as well as the District of Columbia, Puerto Rico, Guam, and the US Virgin Islands. As of March 17, there are more than183,000 cases globally and just over 7,000 deaths, according to the Johns Hopkins University live map. In adults, the virus is thought to have a mean incubation period of five days and commonly causes fever, cough, muscle pain, and pneumonia, however, there is little information on cases and severity in children.

To understand how the virus may impact children, researchers in China studied COVID-19 in children whose symptoms were nonspecific. In a group of 745 children and more than 3,000 adults, just 1.3 percent of children tested positive as opposed to 3.5 percent of adults – a 2.7 percent increase. Of those, 10 children between the ages of 2 months and 15 years were admitted to the hospital. None of the children had a temperature above 39°C (102.2°F) and relatively mild symptoms like sore through, coughing, nasal congestion, and diarrhea. One child was completely asymptomatic, none had the common symptoms seen in adults.

“Compared to adult patients, the 10 pediatric patients reported here had clinically milder symptoms and showed fewer alterations in radiological and laboratory testing parameters,” write the authors in Nature Medicine. “For example, none of the 10 patients showed clear clinical signs or chest X-ray findings consistent with pneumonia, a typical feature seen in the initial adult patients.”

Chest X-rays lacked definite signs of pneumonia, which is a defining feature of the infection in adults, while nasopharyngeal testing – swabs taken from the nose and throat – showed negative. Oddly, tests taken from the rectum were positive for the virus, which raises the possibility of transmission from feces that make its way to the mouth.

All patients received antiviral therapy and recovered without serious incidents. Even though infection in children may be mild, the researchers add that kids can still be shedding the virus long after the symptoms disappear. They add that this further compounds the difficulty of diagnosing children and may require alternative methods of screening.