Why can malaria be harder to vaccine-protect against than some viruses?

Malaria is caused mainly by Plasmodium parasites, not viruses, and the parasite changes dramatically as it moves through the mosquito and human host. These life-cycle changes mean the immune system sees different targets at different times. The parasite also has ways to hide from and manipulate immune responses. Recent vaccines, including RTS,S and R21, have shown that malaria vaccination is possible, but protection is only partial and needs careful deployment. Malaria control still depends on vaccines plus bed nets, insect control, and antimalarial drugs.