Vaccine hesitancy is considered to be a major threat to public health, according to the World Health Organization, even though a number of large studies have shown that vaccines are not dangerous and do not carry a risk of autism.
As a growing number of people opt out of getting vaccinated, diseases that were a thing of the past have been coming back. This year, there have been 314 reported cases of measles in states including New York, Illinois, Texas, Washington, and California. The total number of measles cases in the United States last year was 372.
The Centers for Disease Control and Prevention thinks that some of these infections have been brought to the US from people vacationing abroad. It's estimated that last year, 82 travelers returned to the US carrying the measles virus.