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.

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

In the 18 days since Robert F. Kennedy Jr. was sworn in as secretary of the United States Department of Health and Human Services, his department has postponed or canceled two major vaccine advisory committee meetings,