"With all due respect that is the most impractical idea I think I could have heard." Manius said "For several reasons:
1) Assuming this happens at an airport you are suggesting that a person comes off a flight and has a blood sample, then proceeds through to luggage, Passport Control and Customs and at that point is presented with the results of the test? That's impractical, I'm not that well versed on blood tests but my understanding is that most test results take around 24 hours to come back, with some taking longer than that. Are you suggesting that tourists spend 24 hours in a Heyran airport waiting for results?
2) Time consuming - A 747 aircraft has a maximum capacity of 660 people, so 660 people step off an aircraft in wherever they go for their tests. The person conducting that test is going to be doing more than simply sticking a needle in the arm. They are going to have to take information such as name, nationality and a medical history of sorts, that is going to take time to do safely so let's say ten minutes per person to do the paperwork and the drawing of blood, that means six people per hour so that's a total of 144 people seen by one position within a 24 hour period which means that you need a minimum of four positions to clear just that one flight in terms of drawing blood within a 24 hour period, as it would take four and a half days for one position to draw blood from the entire flight. Added to which you've then got, assuming a busy airport, more flights landing, this creates a backlog which means you have more people coming in than going out and that will eventually and inevitably reach the safe capacity of the airport terminals and that puts people at risk.
3) Damage - Any nation applying this would have to apply it across the board meaning at every point of entry, the hassle of getting into the country then becomes so much that what is intended to protect actually ends up hurting them because it kills off tourism, it potentially even kills off trade and that hurts economies, the nation would be isolating itself.
4) If there's a plague, people are likely to want to put distance between themselves and it, this measure would prevent that plus a plague isn't exactly going to stop at the border is it?
5) Not everyone is going to want to give a blood sample - what are you going to do when someone says "My religion forbids me from giving blood"? You can't force them to give the sample and you can't take a sample without their consent because that is an assault, so you'd have to say "No test no entry" which would be a form of discrimination and could see countries implementing this being hauled through the courts."