puzzled

I just wonder, seeing as the swine flu is meant to be such a major threat, why our government is advising that Brits currently in Mexico return home? Surely if the threat is so great we should be imposing some kind of international lock down in order to contain and eradicate the virus? Not recommending that up to 10,000 potentially infected people arrive in the country.
But hey, what do I know, I'm not an immunologist.