Here's the policy, which should give you the general idea: Recertification Policy
The specific exams/certifications for you would depend on which VCP you already hold.
vSAN Specialist is a "badge" - as you'll see from the policy you need a VCP or VCAP to recertify a VCP.
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Although I am a VMware employee I contribute to VMware Communities voluntarily (ie. not in any official capacity)
VMware Training & Certification blog
