Emergency rooms in the U.S. saw a significant rise in the number of patients with gun injuries during the COVID-19 pandemic, according to a study from the Centers for Disease Control and Prevention released on Thursday.

Of all age groups, those between 0-14 years experienced the largest increase in the proportion of gun injury emergency room visits, the study said. About 40 children and young adolescents with gun injuries visited U.S. emergency rooms each week on average in 2022, up from 2019’s weekly average of about 29.

The study comes as the U.S. reels from its latest deadly school shooting, in which the 28-year-old former student of a Christian grade school in Nashville opened fire on campus and killed three 9-year-olds and three adults on Monday.

The CDC said the COVID-19 pandemic created challenges that might have influenced the risk for firearm injury among children and adolescents, such as social isolation, limited access to mental health services, heightened housing and financial insecurity, and more time spent at home, potentially increasing access to guns.

Researchers who study gun violence in American schools have long warned that the stresses and challenges of the pandemic are worsening the problem.

Monday’s incident in Nashville marked the nation’s 90th school shooting—defined as any incident in which a gun is discharged on school property—of 2023, according to the K-12 School Shooting Database, a website founded by researcher David Riedman. There were 303 such incidents in 2022, the highest of any year in the database, which goes back to 1970.

Although the number of weekly average gun-injury visits to emergency rooms has declined slightly since 2020, there were still 1,170 such visits in 2022, nearly 200 more than the weekly average in 2019, according to the CDC study released Thursday.

The number of patients admitted for firearm injuries began rising in March 2020 and spiked two months later, even as the total number of emergency room visits plummeted, according to the data.

Previous studies have shown that U.S. gun deaths surged during the pandemic, with African Americans at least four times more likely to be killed by a gun than the overall population, and 12 times more likely than a white person, according to CDC data.

This report contains information from Reuters.