Whole Sporozoite Vaccination: Duration between Successive Immunization Dictates the Fate Of Protective Immunity

Whole sporozoite vaccination (WSV) is considered a gold standard for inducing and providing sterile protection against Plasmodium infection. Multiple doses of immunizations with radiation-attenuated sporozoites (RAS) is essential for establishing complete sterile protection against Plasmodium infection in mice as well as in humans. In our recently published article1, we have shown that the pattern of vaccination with RAS determines the degrees of protection in mice and frequent immunization with RAS in optimum time duration helps in generating minimum threshold liver-stage (LS) specific CD8+ T cell memory responses leading to sterile protection. Further, we have shown that the alterations in successive RAS immunization could possibly affect the induction of sterile protection. In summary, animals receiving four successive doses generated 100% sterile protection. However, three successive doses with the same parasite inoculum as four doses, could induce sterile protection in ∼50% mice. Interestingly, mice immunized with the same 3 doses, but with longer gap, could not survive the challenge.