The head of the CDC on Friday urged parents to vaccinate their teenagers against COVID-19, citing a rise in the number of adolescents hospitalized with the disease in March and April. "I am deeply concerned by the number of hospitalized adolescents and saddened to see the number of adolescents who required treatment in intensive care units or mechanical ventilation," CDC director Rochelle Walensky said in a statement that accompanied a new study on teen hospitalizations.