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This is just general advice so not official, you will find that most passengers do not bother with malaria tablets unless they intend to spend some days and nights in a country in the Far East. Ships are mosquito free and if you think that you are going to go into hot steamy interiors then put on a very affective anti-mosquito cream. If you still want more assurance talk to a pharmacist or your doctor....regards Nei.
You would have to be quite mad to do anything else other than consult a medical professional.