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Plasmodium parasites are as stealthy as pathogens come. The malaria-causing single-celled organisms have been adapting to the human lineage for longer than our species has existed, giving them millions of years of training in evading our immune systems and—until recently—an unshakable advantage over vaccine developers.
While SARS-CoV-2, the virus that causes COVID-19, only has 29 proteins, Plasmodium species have thousands. SARS-CoV-2’s spike protein, which it uses to invade human cells, is an obvious bullseye for vaccines, but Plasmodium is a moving target. After mosquitoes inject Plasmodium sporozoites into the bloodstream, the parasites hide away and multiply in liver cells, from which they emerge as bloodborne merozoites, which commence fever-inducing invasions of red blood cells. Some of the parasites shapeshift yet again and are picked up through mosquito bites. For each life stage, Plasmodium transforms its cloak of proteins—a challenge to vaccinologists. Many vaccine efforts have failed ...
