We strongly recommend you purchase appropriate international travel insurance at the time you pay your deposit for any P&O Cruises' itinerary. If you do not purchase travel insurance you may not be able to recover cancellation charges, medical costs, repatriation and other expenses that may arise if things to do not go according to plan.
Australian Medicare, New Zealand ACC and private health insurance will not cover you for any medical costs on board, even on domestic cruises. All cruises (even cruises that do not visit foreign ports) require international travel insurance.
You should not base your insurance decision on the assumption 'it won't happen to me' - accidents or illness can happen to anyone. Daily hospital bills can cost more than AU$5,000 per day.