Scientists have long warned that a warming world is likely to hasten the spread of infectious diseases, making vaccination even more critical to safeguard public health.

And though most scientists hail vaccines as one of public health’s greatest achievements, they have provoked fear, distrust, and contentious resistance since Edward Jenner invented the first vaccine, to prevent smallpox, in the late 1700s.

Health and Human Services Secretary Kennedy and other top officials in the Trump administration have waged an “unprecedented attack on the nation’s evidence-based childhood immunization schedule,” a lawsuit, filed by 15 states, charged on Tuesday. Their actions will make people sicker and strain state resources, the suit claims.