The majority of children hospitalized with multisystem inflammatory syndrome—a rare but serious condition associated with SARS-CoV-2 infection—appear to overcome their most severe symptoms within six months, according to a small observational study published on Monday (May 24) in The Lancet Child and Adolescent Health. The research, which followed 46 young people admitted to Great Ormond Street Hospital (GOSH) in London between April and September, found that some of them continued to have milder problems such as muscle weakness and emotional difficulties even after that six-month period.

“These findings can hopefully signal cautious optimism that many of the most severe effects . . . appear to resolve within six months,” study coauthor Justin Penner of GOSH says in a statement. “However, the persisting fatigue, difficulty exercising, and mental health effects we saw in some children, which can interfere with daily lives, must be closely monitored, and patients should continue to be supported by medical teams with a range of specialisms.”

Doctors first started describing cases of multisystem inflammatory syndrome in children (MIS-C), known as pediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2 (PIMS-TS) in the UK, a couple months into the pandemic. The condition seemed to occur around a month after infection with the virus, and on rare occasions caused multiple organ failure. The CDC has so far recorded 3,742 cases and 35 deaths in the US from MIS-C.

The current study aimed to characterize any long-term effects of the condition. “I think we all didn’t know what to expect,” Penner tells The New York Times. “We didn’t know which body systems would require assistance or become a problem one month, three months, six months down the line.”

The researchers found that six months after being discharged from hospital, just one of the 46 children still showed systemic inflammation. Gastrointestinal and cardiac problems had cleared up in almost all of the children by the time of follow-up, the study reported, although a number of children did show muscular fatigue and anxiety. 

Bernhard Wiedermann, an infectious disease specialist at the Children’s National Hospital in Washington, DC, who was not involved in the work, tells CNN that although the study’s sample size was small, the findings are reassuring. “I’m encouraged that there is this hard data that shows severe organ system damage didn’t seem to be prominent,” Wiedermann says, adding that the findings jibe with research he and his colleagues are carrying out on the condition. 

Because the study didn’t include a control group, it’s not clear whether some of the milder problems seen at the six-month follow-up are due to MIS-C, notes study coauthor Karyn Moshal of GOSH. “The levels of fatigue and muscle weakness we found . . . are concerning and require close monitoring, but it’s difficult to determine whether this finding is caused directly by PIMS-TS or if it’s a result of the disruption in children’s lives that the Covid-19 pandemic has caused on a wider scale,” she says in the statement. “Therefore, it’s crucial that we continue to monitor these conditions as social distancing relaxes and children return to school and more active routines.” 

The team is continuing to track the health of children in the study to look for any problems that might emerge later, as sometimes happens following other critical illnesses, the researchers note in their paper. “We don’t know what the longer-term outcomes will be,” Penner tells the Times. For now, “being able to relay at least what we’ve seen so far to parents has really enabled us to alleviate some of their anxieties about this black box of unknowns with regard to this new condition.”