Figure 1.

Example of a Bite from a Plasmodium vivax Infectious Mosquito Inoculating 15 Sporozoites Consisting of 10 Tachysporozoites That Immediately Develop into Exoerythrocytic Schizonts, and 5 Bradysporozoites That Develop into Hypnozoites.--> In an unvaccinated individual, the 10 tachysporozoites will cause a single primary blood-stage infection, and the hypnozoites will cause up to five relapses. Some hypnozoites may die within liver hepatocytes or activate in batches, giving rise to fewer than five relapses. In an individual receiving a vaccine that immobilises 90% of sporozoites, the efficacy against primary infection will be 0.9¹⁰ = 35%. However, every hypnozoite immobilised may potentially lead to a relapse prevented, and consequently an efficacy against relapses of up to 90%.