My understanding is that Tamiflu will not stop you getting bird flu, but will reduce the symptoms if you do catch it to the extent that it will probably not kill you.
Probably a smart move by VS given the number of lucrative Far East routes they have - if bird flu does start attacking humans then it will start out there first, and this reassurance may delay the point at which crews refuse to operate to such places.
It will be interesting to revisit this thread in 12 months time and see whether it did turn out to be a big deal or not!