Herd immunity is vital. This unwanted comeback has claimed its first American casualty in 12 years, killing a woman in Washington state. It’s a disease “we know we can control with effective immunizations,” one doctor said, noting how unsurprising the tragedy was given the state’s high rate of vaccine exemptions. The woman, who suffered other illnesses, died of measles-related pneumonia after apparently contracting the disease at a medical facility. Her death is raising fears of a possible resurgence, as well as calls for increased immunization to prevent an epidemic.