WASHINGTON, June 26 -- Daisy Hildebrand was eight years old, and she had no underlying health conditions. She died on April 3, 2025, in Lubbock, Texas, from measles pulmonary failure, the second unvaccinated child killed in a single outbreak that had by then infected hundreds of people across the state. Her father, Peter Hildebrand, told reporters afterward that he had no regrets about not vaccinating her, and that if he has other children, they will not receive the MMR shot. Now, as families across the United States board planes for the peak summer travel season, federal health officials are warning that the outbreak that killed Daisy is not over. The numbers have kept climbing.

As of June 18, the Centers for Disease Control and Prevent...