Does anyone get notified when a work item is handed to a coverer?
The assignee changes, so Jira's own notification scheme fires as it does for any reassignment, and the rule posts a comment built from your message text once per work item.
Out of Office sends nothing of its own on top of that.
Related pages
Issue Assignment and Watcher Management - where this is covered in full.
Automations and Workflow - more questions on this topic.
