BBC World Service, this is Ruth Alexander with The Inquiry.

This week, what's behind the anti-vax movement?

This spring in Clallum County in Washington State,

the northwest corner of the northwest corner of the

the United States, a young woman went into hospital.

Within weeks,'d died. Not from her original condition, but from measles,

which she'd caught while she was there from someone who wasn't showing symptoms. It was the first death

from measles in the US in 12 years. Measles infections there are at their highest

since the disease was supposedly eradicated.

Last year, there were more than 20 outbreaks affecting hundreds of people.

When one infected person visited Disneyland, 40 people caught it and the disease spread to six states.

Meals is highly contagious.

The reason the number of cases has been rising is that the number of people

vaccinated against measles has been falling. More and more parents have been

refusing to immunize their children. The influence of a loose

group of fringe campaigners against immunisation, anti-vaxes as they're known, has been spreading,

and with it disease.

Our inquiry this week isn't about the safety of vaccines.

Yes, they can cause adverse reactions in a small number of people like many medicines, but the accepted science is that the benefits far outweigh the risks.

And that's why none of our expert witnesses this week is an anti-vaxer.

Instead, our inquiry is asking why, given the body of scientific

evidence, given the advice of national and global health authorities, childhood immunization has become so controversial.

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