[CentOS] CentOS-6 reboots

I am now in receipt of an update to qemu-img and qemu-kvm. My practice up to now has been to restart the virtual host after applying qemu updates. This in turn implies that all of the virtual guests on that host also will need restarting since suspending them takes much, much longer than a restart.

The issue of whether or not the requirement to reboot servers based on CentOS was increasing or not was recently raised.

My question then: Is a restart of the host following applying these updates actually necessary? If not then what is the procedure to get them to take effect on existing virtual guests?