<Unless I'm missing something ... quick mutation of the virus>

It is a long article but you missed the part at the beginning of the article explaining that malaria is not caused by a virus or bacteria but a parasite.

Also the chart labelled 'Vaccine Discovery' which clearly shows no previously existing vaccines against parasites.

Also, the world map showing where Malaria has not been eradicated clearly indicates that it is found in the tropical belt where unfortunately a lot of poor countries exist.