In an SDDC, availability zones are collections of infrastructure components. Regions support disaster recovery solutions and allow you to place workloads closer to your customers. Typically multiple availability zones form a single region.
This VMware Validated Design uses two regions, but uses only one availability zone in each region.
Some of the use cases, such as the VMware Validated Design for Micro-Segmentation, are validated for one regions. However, they can be expanded to use two regions, and from there to use two availability zones.
The following diagram shows how the design could be expanded to include multiple availability zones.