Using Vivoactive for Zwift running

I have an original Vivoactive watch and ant + dongle and have just started using Zwift for running. Do I need to use a foot pod or can I just use the watch. If the foot pod is not required, how do I pair the vivoactive?
I have been using a Suunto foot pod but have found the readings very temperamental at low speeds, even after several calibrations.
Thanks for your help.