According to a new study, health care providers may be overcounting the number of children hospitalized for COVID-19, overestimating the disease’s minor impact on children.

Stanford University School of Medicine researchers examined COVID-19 data from Lucile Packard Children’s Hospital Stanford from May 10, 2020, to February 10, 2021. 117 patients under the age of 18 were either tested positive for SARS-CoV-2 at the hospital or were hospitalized for multisystem inflammatory syndrome in children, or MIS-C, during the nine-month period.

According to the study published Wednesday in the peer-reviewed journal Hospital Pediatrics, nearly 40% of the 117 children with COVID-19 were asymptomatic. Approximately 45 percent of those hospitalizations were deemed unlikely to be caused by the virus.

“It confirms what other studies have shown, which is that children in general are relatively mildly affected by the infection,” said Dr. Asim Ahmed, a pediatric infectious disease specialist who was not involved in the study and senior medical director at Karius, an infectious disease diagnostic company.

According to Dr. Alan Schroeder, study co-author and clinical professor of pediatric critical care and pediatric hospital medicine at Stanford, it is critical to distinguish between children who test positive but are asymptomatic and those who are hospitalized for COVID-19 in order to understand how the disease truly affects the pediatric population.

“Our goal is to have accurate data on how sick children are getting,” he explained. “If we rely on positive SARS-CoV-2 test results from hospitals, we are inflating the actual risk of hospitalization from the disease in children by about twofold.” According to the study, approximately 28% of patients had mild to moderate COVID-19, 7.7% had severe illness, 12.8% had critical illness, and 12% had MIS-C, a serious condition that appears to be linked to COVID-19 in which some organs and tissues can become severely inflamed.

The study’s authors believe that many children will develop other illnesses that necessitate hospitalization and then test positive for SARS-CoV-2 without realizing they were infected. Though this data may be useful for better understanding community transmission, it does not accurately measure the rate at which children become ill with COVID-19, according to lead author Dr. Roshni Mathew, clinical associate professor of pediatric infectious diseases at Stanford.

“Knowing that a child is hospitalized and has the virus is insufficient information to determine if they are actually sick with COVID-19,” she explained. Some of the study’s limitations, according to the researchers, may have influenced its findings. For example, the study sample size is small in comparison to other parts of the country where COVID-19 may be more prevalent.

According to Ahmed, data may be skewed due to the unusually low hospitalization rates at pediatric centers. These were due in part to parents’ reluctance to take their children to a hospital for fear of them becoming ill, as well as the low prevalence of illnesses, such as the flu, after public health measures to control the pandemic were implemented.

“Although hospitalization patterns and practices were similar in adult hospitals (during the pandemic), they were very different in pediatric hospitals,” he explained. “The overall census for pediatric hospitals was quite low.”

Although severe disease is uncommon in children with COVID-19, health experts still advise parents to get their children vaccinated because severe disease, hospitalizations, and deaths do occur. According to Dr. John Williams, chief of the division of pediatric infectious diseases at UPMC Children’s Hospital of Pittsburgh, approximately 300 children have died from COVID-19 in the United States. He believes that immunizing children is critical to preventing coronavirus transmission and protecting people who are immunocompromised and may not respond as well to COVID-19 vaccines.  “It’s an important study, and it’s an area that we need to keep learning about,” he said. “But it should not be interpreted to say that children don’t need vaccines.”