Whichever Indian Ocean island you have chosen for your holidays, you should make sure your basic vaccination is up to date: DTaP, hepatitis B and even hepatitis A for flights to Madagascar, the Seychelles, Mayotte, the Maldives and Zanzibar. Other vaccines (meningitis A and C and even rabies) are also required for some islands in this global region.
Réunion, Mauritius, the Seychelles and the Maldives do not require antimalarial medication. You should consider it for other destinations in the Indian Ocean.
Although Réunion and Mayotte are French overseas departments and regions (meaning the French Carte Vitale healthcare care is valid there), the others are not. Check that you have personal insurance to cover and repatriate you if you have problems during your trip.