Even though children are more likely to be spared serious illness from COVID-19, the so-called long COVID-19 in children has brought symptoms like headache and fatigue lasting a month or more.

The U.S. Centers for Disease Control and Prevention (CDC) reports that long COVID-19 appears to be less common in children and adolescents than adults. The most common symptoms among young people after an acute case of COVID-19 have been fatigue, headache, trouble sleeping, trouble concentrating, muscle and joint pain, anxiety and cough.

Even children and adolescents who did not experience symptoms when they had COVID-19 could develop long COVID-19 symptoms weeks later, the CDC reported.

“We’re still learning about the long-term health effects of COVID-19 in children. My best advice is for anyone 5 and over to get vaccinated to reduce their chances of getting sick in the first place,” said Gary S. Marshall, M.D., pediatric infectious diseases specialist with Norton Children’s Infectious Diseases, affiliated with the UofL School of Medicine.

Nearly 6.4 million children in the United States have had COVID-19. Researchers are uncertain how many of them also experienced post-COVID-19 symptoms.

Some clues have come from abroad.

British researchers, using data from a smartphone app, found that out of more than 250,000 children, fewer than 1 in 20 reported symptoms lasting more than 28 days. Fewer than 1 in 50 reported symptoms lasting more than 56 days. The most common symptoms they found were lack of smell, headache, sore throat and fatigue.

In Italy, interviews with 129 children ages 6 to 16 found more than a third still had one or two symptoms four months or more after the infection. Symptoms included trouble sleeping, fatigue, muscle pain and cold-like symptoms.

One reason it’s so hard to figure out how many children get long COVID-19 is because there is no accepted definition of what constitutes the condition. Some 200 symptoms have been attributed to long COVID-19 in children, which is also called post-COVID-19, long-haul COVID-19, post-acute COVID-19, long-term effects of COVID-19, or chronic COVID-19.

Studies on long COVID-19 in children overwhelmingly were conducted before the highly infectious delta variant spread around the world. It’s unclear whether the risk of developing long COVID-19 is higher with the delta variant.

In September alone, about 850,000 children in the United States had COVID-19, according to the American Academy of Pediatrics and the Children’s Hospital Association. Because of the large number of children getting COVID-19, even a small percentage of children with long COVID-19 could have a big effect on schools.