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.

WASHINGTON—Amid a growing outbreak of measles in Texas, recently confirmed Health Secretary Robert F. Kennedy Jr. is urging parents to vaccinate their children against the disease.