Originally Posted by
hailstorm
Indeed. And you would want to be perpetually vigilant against such a threat, as we have been perpetually vigilant against hijacking planes and flying them into buildings, an event that has not happened in over 20 years now.
That analogy does not hold. A plane hijacking is not a random event. With no prevention measures it can occur via someone's conscious decision and it is a known fact that there are people who exist right now that would do such a thing given the opportunity and a lack of measures to stop them. Protections against it have been deployed that are proportional in their risk-reduction against the cost of failure.
The measures to guarantee that a foreign virus of high lethality cannot enter your country come at an immense cost that cannot at all be said to be proportional to the risk. What would be the basis? You'd have only historical data which would tell you that there haven't been any viruses where the devastation would be worth the economic damage to a country (which has its own devastation to human lives, it's not just numbers on a stock ticker) of completely closing oneself off to the world.
Perhaps I am just misunderstanding what you mean by vigilance and what measures one would take, but I am basing this on your remark around the only way to prevent entry of a virus.