I use Avast on a personal desktop, and have little idea about networks.
But the basics (in principle) as regards this question probably aren't too different.
1) The VRDB takes a while to gather the required information about the files it will store info on; it is not an instant process. (And if the files were infected to start with, it wold actually be useless. It needs clean files to store.) I've seen it take well over an hour.
2) Not all files that belong to the OS are stored. Only a select few of the "then" commonly- attacked ones, when the VRDB concept was invented.
3) The only way Avast could repair a file, is if (a) it had a bit of viral code attached to it and was previously a legitimate file; (b) it was one of the files present in the VRDB store; and (c) if a clean copy of that file was actually present in the VRDB.
4) It's old technology, which is one reason it is being dropped in version 5. Most infections in todays environment are trojans, worms, rootkits etc. The entire body of the file is an infection; there is no point in attempting to clean them, quarantining or deletion should be the only options.
On your network, are the detections mainly viruses? Or trojans etc? If the latter, Avast should, in most cases, be able to move them to the chest (quarantine). If the former, repair would have to be carried out, (I think) manually, using current clean files from an OS disk or similar, for the reasons stated above.
I would actually be fairly surprised if your network has a large number of actual viruses, unless an extremely inefficient AV had been used since the time viruses were more common. (Say, 4 - 7 years back).
It is more likely they are actual trojans etc, ie: unable to be repaired (and no point trying to.)
