Casdon
Smoked salmon contains bacteria from the off MaizieD, because generally it is not cooked, it is cold smoked. The bacteria can include listeria, which is why vulnerable people should not eat it. Hot-smoked salmon is obviously safer.
I recall from my ancient food hygiene certificate that, given the right conditions, bacteria can multiply at a very fast rate, dividing every 20 minutes.
I'm aware that vacuum sealed smoked salmon kept in a fridge is not optimum conditions for food poisoning bacteria, but I then assume that they do multiply, albeit very slowly, and that a 'use by' date is calculated on an anticipated bacterial load which is considered to be non hazardous?
This whole issue intrigues me.. any bacteriologists here?