Humans headed to the ISS go into quarantine for 2 weeks before launch, and if they have medical problems during that time the backup crew takes over.
Was this procedure also applied when going to the Mir space station? (And was the duration 2 weeks like for the ISS?)
Mir became somewhat infested with microbes and the like and had quite a bad smell.
Would some of this have been avoided with (longer?) quarantines before launch?
Yes.
It's still early when Tsibliyev slips out of the quarantine rooms in the Prophylactorum ...
Dragonfly, Bryan Burrough, page 68
This was in preparation for the Soyuz-25 mission to Mir.
Crewmembers flying to Mir on the Shuttle went through a normal Shuttle quarantine.
"We'd like to thank all the people down on Earth," he continued. "There was a tremendous amount of teamwork required to put something like this together. We had discussions all the way up when we were in crew quarters, in quarantine, just before coming up regarding the procedures and what do we do if we have failures. Both sides of the ocean worked on this flight for a long time and we want to thank everybody who worked on it."
Jim Wetherbee, STS-86 (7th shuttle docking to Mir) commander, quoted here.
