The United States has seen an increase in COVID-19 adolescent hospitalization rates in April, according to a report released by the U.S. Centers for Disease Control and Prevention (CDC) on Friday.

Most COVID-19-associated hospitalizations occur in older adults, but severe disease that requires hospitalization occurs in all age groups, including adolescents aged 12 to 17 years.

The CDC examined COVID-19-associated hospitalizations among adolescents aged 12 to 17 years, including demographic and clinical characteristics of adolescents admitted during January 1 to March 31, and hospitalization rates among adolescents during March and April.

COVID-19 adolescent hospitalization rates peaked at 2.1 per 100,000 in early January 2021, declined to 0.6 in mid-March, and rose to 1.3 in April, according to CDC data.

Among hospitalized adolescents, nearly one third required intensive care unit admission, and five percent required invasive mechanical ventilation. No associated deaths occurred.

"Recent increased hospitalization rates in spring and potential for severe disease reinforce the importance of continued COVID-19 prevention measures, including vaccination and correct and consistent mask wearing among persons not fully vaccinated or when required," the CDC said in a report.

"I am deeply concerned by the numbers of hospitalized adolescents and saddened to see the number of adolescents who required treatment in intensive care units or mechanical ventilation," said CDC Director Rochelle Walensky in a statement.

Until they are fully vaccinated, adolescents should continue to wear masks and take precautions when around others who are not vaccinated to protect themselves, and their family, friends, and community, Walensky said.