Short answer ....No. Long answer Not really ....Nei.
Why not refer to the information issued by P&O to all their passengers, and also detailed in their brochures? Happy cruising.
We have been travelling to the Caribbean every year since the mid 90's. We had injections done the first time we went and have been keeping them up to date ever since. They are not complusory, but these are tropical islands. If you were staying on an island I think you should have them but on a cruise the risk is low. Go and see the practice nurse at your local GP surgery for advice. The injections are free there.