In my experience and even though you might have reformatted your PC check the files you are putting back are free from virus's, malware etc.
That wording needs a little tweaking.
My definition of restore from backup is that of restoring your personal files.
I do not believe in the restoration of software or operating system components from backups.
Thus, the restoration of an infected file, whilst evidently not a good thing, is also fairly harmless because the virus is not active at that stage.
One would also hope that you take the wipe/restore opportunity to :
(a) strengthen your virus defences before restoring
(b) update and patch your system fully before restoring
(c) perhaps take the opportunity to have a spring clean and not restore unnecessary files or directories.
(d) run a virus scan on restored files and directories