Is site-to-site VPN required for Hyper-V Replica?

I am trying to figure out if a site-to-site VPN is required to do Hyper-V Replica from one site to another site over the Internet? If it is not required, is the security built into Hyper-V Replica sufficient enough to be exposed directly to the Internet? Thanks for your help understanding this.

Regards,

Warren-G2