When it comes to ClamAV you should wait for Joe or Eric to answer to your question because ClamAV is edited and distributed by Virtualmin. There was some problems in the past (and still few of them are pending) so Joe made some modifications. For example just updating ClamAV from EPEL will cause a lot of problems with Virtualmin so you should pay attention what patches to apply. Best would be to make full server backup and then try otherwise you could end with broken ClamAV and Virtualmin.
I hate this status quo with ClamAV but Joe several times complained how this software is bugged as hell and i think he is right.