New Zealand is in the thick of its worst measles epidemic in 22 years, with more than 850 cases so far. As one vaccinologist says, it was predictable, entirely preventable and the government were warned.

Where did this outbreak come from?


What's the bigger picture, here?

How does this stack up with previous outbreaks?

So how does the MMR vaccine actually work – and what's herd immunity?

What's being – and should be - done?