The measles outbreak in Texas has sparked debate over the use of vitamin A, with some health experts warning it may not be effective.

Kennedy's acknowledgement of the value of the measles vaccine comes as the outbreak that began in Texas continues to grow. So far, nearly 150 cases and one death—the first U.S. fatality from the disease in more than 10 years—have been confirmed. It's the largest measles outbreak in the U.S. in decades.

Robert F. Kennedy Jr., secretary of the Department of Health and Human Services (HHS), said the measles outbreak in west Texas is a “call to action” as he encouraged parents to consider whether to get their children vaccinated.