During the 2017 Worldwide Developers Conference (WWDC), Apple announced Metal 2, the second version of the graphics API. Metal 2 includes support for VR content creation, and Apple said Valve, Unity, and Unreal would bring their VR tools to the Mac.
Today, Epic Games are releasing early access support for virtual reality development on Mac platforms through the Unreal Engine Github.
Mac VR support, along with full Metal 2 features will ship in Unreal Engine 4.18. You can expect previews to arrive in September and a full release is in early October.