Until very recently, if there was one silver lining to the pandemic, it was that kids seemed to escape the worst of the virus. Very few became seriously ill or even mildly sick, compared with adults. But now that hopeful aspect may be fading. The number of children hospitalized with COVID has skyrocketed in recent weeks as the Omicron variant fueled a surge of infections, raising concerns that the latest version of the coronavirus may pose a greater threat to children.
Nationwide, an average of 881 children under age 17 are being admitted to hospitals with COVID each day, according to the most recent data from the Centers for Disease Control and Prevention. Hospitalizations of children under the age of five, who are not eligible for the COVID vaccine, have soared to levels two to four times that of previous peaks.
Experts believe the jump in pediatric hospitalizations is likely the result of a confluence of factors. One of them is Omicron’s more contagious nature, and another may be the variant’s newfound preference for airway passages above the lungs, which can be more easily blocked in small children.
The big issue is that Omicron is infecting a lot more people. “We refer to this as the denominator phenomenon,” says Susan Coffin, an infectious disease specialist at Children’s Hospital of Philadelphia. The hospitalization rate is calculated by dividing the number of hospitalizations—the numerator—by the number of known cases—the denominator. If the denominator becomes a bigger number, so will the numerator, the thinking goes.
And indeed, a recent report from the American Academy of Pediatrics indicates that the denominator—specifically, the number of pediatric cases—is growing at an enormous rate. Out of the nearly 9.5 million children who have tested positive for COVID-19 since the beginning of the pandemic, nearly 20 percent of these cases occurred in just the first two weeks of January.
Thus far, there are no signs that the cases caused by Omicron are more severe. If anything, preliminary evidence suggests the opposite may be true. Rong Xu, a data scientist at Case Western Reserve University, analyzed health records from nearly 80,000 children under age five who developed COVID-19 before and after the emergence of Omicron. She found that the risk of hospitalization in those who became sick when that variant was dominant was one third of what was observed when Delta reigned supreme (1 percent versus 3 percent). The study is consistent with previous work showing similar trends for children of all ages and is supported by a recent analysis of COVID patients in California. (All of this research has appeared in preprint papers, which have not yet been peer-reviewed or published in a scientific journal.)
So why the jump in hospitalized children? “The risk of hospitalization is not zero,” Xu says. “So if you multiply it by a big number—if more kids are getting infected—you are going to see a lot more kids in the hospital.”
Though scientists are still teasing apart the properties of Omicron that enable it spread so rapidly among children and adults alike, one aspect that could give the variant a leg up is its ability to evade the immune response. In the first waves of the pandemic, kids fared better than adults in large part because children have more robust innate immune systems, which mount rapid initial responses to invading microbes. Adults, in contrast, have better adaptive immune systems, which respond effectively after an infection has begun to take hold in the body. “Everybody started out with a clean slate, having never seen the virus,” says Betsy Herold, a pediatric infectious disease physician at the Albert Einstein College of Medicine. In a study published in 2020, Herold showed that children mounted a swift innate immune response to COVID, churning out potent antiviral proteins known as interferons and interleukins that quashed the coronavirus early in infection.
But two years in, and a Greek alphabet of viral variants later, circumstances have changed. Researchers at the Quantitative Biosciences Institute at the University of California, San Francisco, and their colleagues recently reported that SARS-CoV-2 has picked up mutations that weaken the innate immune response. Molecular biologist Mehdi Bouhaddou, who co-led the research, says that while he and his coworkers’ experiments focused on the Alpha variant, the Delta and Omicron variants also carry the same immunity-disabling mutations. But because those mutations appeared in all three variants, they alone cannot explain fluctuations in pediatric hospitalizations. Both Bouhaddou and Herold are launching studies to investigate whether Omicron has a unique impact on innate immunity. “My hunch is that the innate immune system is still strong,” Herold says. “But it’s a balance, right? If you have a ton of virus, then no matter how good your innate response is, some of that virus is going to win out.”
And with Omicron, there is a ton of virus. This variant replicates 70 times faster than Delta in human airways, according to preliminary data shared in a news release from the University of Hong Kong. That same research and a slew of animal studies show that the variant has a harder time multiplying in lung tissue, suggesting why it might cause less severe disease. This evolutionary journey into a more transmissible but milder version is somewhat expected, though in no way guaranteed, Bouhaddou says. “Viruses typically evolve to become less dangerous over time,” he adds.
Still, Omicron’s predilection for the respiratory tract above the lungs could spell trouble for the youngest children, whose airways are narrower and less developed. Coffin says it is easier for these tiny airways to be obstructed by mucus and inflammation, causing infants and toddlers to develop wheezing or croup, a disease known for its characteristic barking cough. “These are classic syndromes of childhood, and we are pretty adept at taking care of them,” she says. Though these conditions can land children in the hospital, they are easily treatable, regardless of whether they are caused by SARS-CoV-2 or another virus.
In some parts of the country, pediatric hospitalizations are now starting to edge downward as case counts begin to ease. Experts recommend that families trying to weather this wave continue to do what they can to keep kids safe: getting vaccinations and boosters when possible, wearing masks and avoiding social activities at the first sign of symptoms. “These are all things that have been proven time and time again over the past 20 months to work,” Coffin says. “And they work really well against Omicron, too.”