Contrariwise, when doing a coverup, goverments attempt to behave exactly as if they're telling the truth. This is the eternal problem with a liar - if you can't tell when he's lying, you can't trust anything he says.

In a society with a decent press, journalists would try to find out the truth, and would act as a check. Unfortunately, we have the Daily Mail and Melanie Philips instead. Not to mention 'health' sections which seem to spend their entire time promoting woo and detox diets and the like.

Well, The Guardian did its best, I think.

Dr G is a godsend, and I would hope that his colleagues are getting into the habit of running stuff quickly past him for a sanity check.

How do substantial outbreaks in a measles-free country trace back to here? Or is that a 'by chance' measles-free country rather than one that has actively achieved measles-free by vaccinations?

If you have somewhere with no endemic measles, and you have full herd immunity (greater than 95% are unable to catch it), then any local outbreak quickly dies out. You no longer have locally caused outbreaks.

Introduce one infectious child, or a family thereof, from outside, and they may well encounter a few dozen other children previously-unexposed. Some of those will be able to catch it. However, the way that social circles work, those infected children will encounter mostly other children that have now been exposed, so new infections taper off quickly.

Quite how many 'substantial' is is an unanswered question. But the tracing part is relatively easy: if you have a population without a disease, a new person joins that population, and members of that population then start presenting with the disease, you examine that new member.