The auto-replies (out of office responses) will be considered as replies affecting SLA calculation and performance metrics related to the ticket. To avoid that, set up an automation rule (under Admin > Workflows > Automations > Ticket updates > New rule) to close the tickets automatically when these auto-responses come through.
When an action performed by:
Involves any of these events:
Reply is sent
On tickets with these properties:
In Tickets > If Last Interactions > Contains > Out Of Office, Unavailable
Perform these actions:
Set Status as > Closed