Severe COVID-19 in children during the Omicron BA.5 and XBB waves: clinical characteristics and risk factors
This retrospective study of 519 hospitalized children in Xiamen reveals that clinical severity significantly decreased during the XBB wave compared to the Omicron BA.5 wave, identifying neurological symptoms as the strongest predictor of severe disease while highlighting infancy, toddlerhood, hyponatremia, and elevated neutrophil counts as key independent risk factors, whereas underlying comorbidities and co-infections were not significantly associated with severe outcomes.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine the human body as a bustling city, and the immune system as its dedicated police force. When a virus like SARS-CoV-2 (the germ behind COVID-19) invades, it's like a riot breaking out in the streets. For a long time, scientists thought that if this riot happened in children, it would mostly be a noisy disturbance in the respiratory district—the lungs and throat—causing coughs and fevers but rarely shutting down the whole city. However, as the virus kept changing its "disguise" (evolving into new variants like Omicron), the nature of the riot changed. Sometimes, the chaos doesn't just stay in the lungs; it spreads to the city's central command center: the brain. This is where things get tricky. Doctors need to know: when a child gets sick with a new version of the virus, what are the real warning signs that the situation is about to go from a minor scuffle to a full-blown emergency? Is it the number of other germs attacking at the same time? Is it the child's age? Or is it something happening inside the brain that we haven't been watching closely enough?
This study, conducted by doctors at The Fifth Hospital of Xiamen, acts like a detective's report on a specific period of time (from late 2022 to late 2025). They looked at 519 children who were sick enough to be hospitalized with COVID-19. They wanted to compare two different eras of the virus: the "BA.5" wave and the later "XBB" wave. Think of BA.5 as a rougher, more chaotic version of the virus, and XBB as a slightly more subdued, though still tricky, successor. The researchers dug through medical records to see who got really sick, who stayed in the hospital longer, and what specific clues in their blood or behavior predicted a severe outcome. They were particularly interested in whether having other infections (co-infections) or existing health problems made the virus worse, or if something else was the real culprit.
The investigation revealed a surprising shift in the landscape. When the XBB wave hit, the situation for hospitalized children actually improved compared to the BA.5 days. Fewer kids needed oxygen, their hospital stays were shorter (a median of 3 days instead of 4), and fewer developed severe complications. It was as if the virus had lost some of its "bite" over time, perhaps because more people had built up defenses or because the virus itself became less aggressive.
However, the most critical discovery wasn't about the virus getting weaker; it was about who got hurt the most and how. The study found that the biggest danger wasn't the number of other germs attacking the child (co-infections) or even having a pre-existing health condition like mild asthma or allergies. In fact, the data showed that having other infections didn't independently make the disease more severe. Instead, the true "smoking gun" for severe or critical illness was neurological symptoms.
In the group of children who became critically ill, a massive 69% showed signs of trouble in their central command center: seizures, confusion, or loss of consciousness. In contrast, only about 2% of kids with mild or moderate cases had these symptoms. The researchers concluded that if a child with COVID-19 starts having a seizure or acting confused, that is the strongest possible warning sign that they are in the danger zone, far more so than just having a bad cough or a fever.
The study also identified a few other specific risk factors that acted like "speed bumps" on the road to recovery. Being very young—specifically an infant (under 1 year) or a toddler (1 to 3 years old)—significantly increased the odds of severe illness. Additionally, two specific blood markers were red flags: having low sodium levels (hyponatremia) and having an elevated count of neutrophils (a type of white blood cell). The presence of low sodium was like a sign that the body's fluid balance was tipping dangerously, often linked to the brain swelling or inflammation.
Interestingly, the study ruled out some things people might have expected to be major risks. Having a history of febrile seizures (seizures caused by past fevers) or having other infections alongside COVID-19 did not independently predict severe disease in this group. The severity seemed driven by the virus's direct impact on the brain and the body's inflammatory response, rather than by a "double infection" scenario.
The authors suggest that doctors should pay extra attention to the brain and the blood's salt levels when treating young children with COVID-19. If a toddler or infant comes in with a fever and starts acting strangely or having a seizure, the medical team should treat it as a high-risk emergency, regardless of how well the child is breathing. While the virus has evolved to be less deadly overall, the path to severe illness in children is now clearly marked by neurological distress and specific blood chemistry changes, not by the presence of other germs. This insight helps doctors prioritize who needs the most urgent care, ensuring that the "central command" of the body gets the protection it needs before the situation spirals out of control.
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