Casual vacancy of statutory auditor

pritesh (trainee company secretary)   (23 Points)

21 February 2018  
our company got listed in dec 2017 and now it is mandatory for us to appoint peer review auditor.

our existing auditor is not peer review auditor.

so in case we take resignation from existing auditor will this amount to casual vacasy due to resignation or disqualification.

do we have to take shareholders approval for appointment of peer review auditor?