Pig Disease kills People and Bird-Flu kills Ducks, In Bird-Flu-Free Vietnam!

It was only last week that Vietnam was busy declaring its provinces ”Bird-Flu-Free”.
The criterion for this Bird-Flu-Free status was the completely illogical “no infection in any 21 consecutive days” rule.

How did this rule come about?
Who was responsible for this ruling?
Does the World Health Organisation agree with this totally mad criterion?
If not then why is there a deafening silence [...]