Even the littlest children can experience long Covid, according to a large study, one of the first of its kind to include infants and toddlers.
The study published Wednesday in the journal The Lancet Child & Adolescent Health included 44,000 children in Denmark ranging in ages zero through 14 years old. Of the children, 11,000 had tested positive for Covid-19 between January 2020 and July 2021.
While symptoms associated with long Covid are general ailments children can experience even without Covid -- headaches, mood swings, stomach problems and tiredness -- the children in the study who had previously tested positive for Covid were more likely to experience at least one symptom for two months or more than the children who never tested positive for Covid.
The study also revealed that a third of children who had tested positive for Covid experienced at least one long-term symptom that was not present before testing positive.
The most common symptoms varied by age. For children up through age 3, it was mood swings, rashes and stomach aches. Children 4 to 11 years old also experienced memory and concentration problems. For the 12- to 14-year-olds, it was memory and concentration issues, mood swings and fatigue.
Children 3 and under seemed to have the most problems compared with those children not diagnosed with Covid-19 -- 40% experienced symptoms two months after testing positive compared with the 27% in the group that did not have Covid.
"Our findings align with previous studies of long Covid and adolescents showing that although the chances of children experiencing long Covid is low especially compared to group to the control group, it must be recognized and treated seriously," said study co-author Selina Kikkenborg Berg, a professor of cardiology at Rigshospitalet in Copenhagen, Denmark.
It is still unclear how many kids have long Covid and for how long, because there is not enough research on it in this age group, some experts say.
A 2021 study suggested more than half of children between age 6 and 16 had at least one symptom that lasted more than four months.
There are no specific tests for long Covid. It's not clear which children will have it, as it can happen even when a child has a mild case of Covid-19.
In addition to showing scientists the characteristics of long Covid in children, the study also showed that even the children who did not get Covid felt the impact of the pandemic. That group reported a few more psychological and social problems than children who had Covid.
Dr. Michael Absoud, a pediatrician who specializes in neurodevelopmental issues who did not work on the study, told the Science Media Center in the UK that he found that fact intriguing.
"The most striking finding of this study is the higher quality of life and lower anxiety scores in older children who had tested positive for Covid-19. This provides further confirmation, that although mercifully children are resilient to the direct impacts of Covid, they have been significantly impacted by the indirect impacts of the pandemic (school closures, repeated quarantines, and reduced therapies) and anxiety inducing media messaging. It is likely that society has under-estimated longer term impact of the pandemic disruption rather than the virus on all children, and the urgent need for recovery of health and wellbeing services," Absoud said.
"Nonetheless it is still important to identify the small proportion of children who are taking longer to recover from COVID, whilst supporting all children with persistent symptoms regardless of cause," he added.
Dr. Amy Edwards, a pediatric infectious disease specialist who manages the long Covid clinic at UH Rainbow Babies and Children's Hospital in Cleveland, did not work on the study, but said the work was important because it is more proof that some children develop long Covid.
She said she still regularly encounters people who do not believe that there is such a thing.
"There is a debate going on in both the medical world and in society, about whether all these kids are complaining about headaches and anxiety and stomachs, aches, and dizziness as to whether this is Covid or the stress of the pandemic. Yes, the pandemic did affect children in a negative way, but then you layer on Covid on top of that, and you see that there is something really going on here," Edwards said.
Acknowledging long Covid can be a problem may encourage more parents to vaccinate their children so they don't get long Covid in the first place. Studies like this may also encourage parents to be on the look out for symptoms, so they can get the child help if they need it.
"It's become clear that this isn't an isolated phenomenon. It's showing up in studies in more than one country. It's happening in more kids than maybe we originally thought," Edwards said. "We're talking about not small numbers of children when you think of how many Covid cases there have been. So just continuing to get the word out there matters."