Malaria and Anambas
No cases of malaria have been found in anambas since 2014, during which several construction laborers on one of the far-flung Anambas islands were found to carry the bug.
Furthermore, as this malaria cluster was promptly eradicated, it's believed that this mini-outbreak was caused by the infection being brought in by the laborers from their mainland Indonesian village.
In fact, according to Fit for Travel, based in the UK, the Riau region is considered "low to no risk" when it comes to malaria. And if you're going to travel to this part of Indonesia, anti-malarial medication is not usually advised.
That being said, since there are other areas within Indonesia that are not yet malaria-free, and since Anambas is usually just one of several Indonesian regions visited by travelers, it would make sense to take prophylactics like Malarone, and to continue taking it whilst in Anambas, particularly when traveling on to areas in Indonesia where malaria has not yet been eradicated.
In addition, whilst mosquitoes are not as plentiful in Anambas as some of other South-east Asian regions, likely the result of the various local anti-mosquito measures in place, it's still a good idea to apply repellent such as DEET when traveling to more rural areas.
Bottom line: malaria is not endemic in Anambas and the islands can be considered malaria-free.
Disclaimer: The information here is not medical advice and should not be construed as such.