since the beginning of vaccines. Vaccines date back to the the research of Edward Jenner,

a doctor who was working in rural Britain in the 1700s. He noticed that on the farm,

the milk maids didn't get smallpox in the way everyone else around him seemed to. So

one by one, he started scraping pus from sick cows into the skin of his family members,

and miraculously they didn't get sick. His discovery led to the smallpox vaccine, and

later the world's first and only infectious disease eradication. "This child has what's

called active immunity. He has acquired this active immunity by actually having the disease.

Fortunately, there's a safer way to get immunity. This is through vaccination." Edward Jenner

was basically ostracized from his community. People thought it was disgusting that he would

inject his family with pathogens from a sick animal. Fast forward to today, and the same

kinds of concerns continue. Jenny McCarthy:"We do not need that many vaccines." J.B. Handley:

"People overly generalize about them as if they're only good." Doctors have to ask brand

new parents to give otherwise healthy babies dozens of needles, based on the promise that

they'll avoid some future, abstract disease. One discredited paper made many, many parents

think there is a link between the Measles, Mumps, Rubella vaccine and Autism. Andrew

Wakefield: "The parents understand it. They get it. Because they've lived it." Anderson

Cooper: "The messages from the BMJ could not be clearrer or more shocking: Wakefield's

research, they contend, has been a fraud." And we have other anti-vaxxers today who aren't

only worried about autism. There are the delayers like Rand Paul: "We sometimes give five and

six vaccines all at one time, I chose to have mine delayed." There are deniers of all stripes.

There are the Orthodox Jews in Brooklyn. There are the parents of children with medical conditions

who have to opt out. There are even unvaccinated kids visiting Disneyland. The majority of

last year's massive uptick in measles cases actually involved the Amish of Ohio. More

than 350 people there were infected by one man who had travelled to the Philippines.

These outbreaks of vaccine-preventable diseases in the US typically happen just like that.

An un-immunized person travels to a place where one of these diseases is circulating,

returns to his community with other similarly un-immunized people. And boom. We don't remember

what Measles or Polio or Hepatitis B look like and felt like. Elizabeth Warren: "These

vaccines work so well that the memory of these diseases has faded." Viruses and bacteria

don't know any borders. All it takes is a single traveler to spark an outbreak, even

in the happiest place on earth.