Wellness influencers and anti-vaccine activists have reacted to measles outbreaks by spreading misinformation about the disease. "The truth is, measles is not a very serious illness when you're a child," Mary Holland, president of Children's Health Defense, said.

Measles is characterized by fever, flu-like symptoms, and an itchy skin rash, and sometimes leads to serious complications such as pneumonia, seizures, and brain damage. For every 1,000 cases of measles, about 200 children may be hospitalized, 50 may contract pneumonia, one child may develop brain inflammation.