Humoral responses against the C-terminal region of merozoite surface protein 1 can be remembered for more than 30 years in persons exposed to Plasmodium vivax.

Most people infected with Plasmodium vivax malaria developed antibodies against the C-terminal region of P. vivax merozoite surface protein (PvMSP1c) and the antibodies are sustained for a period up to 10 months after anti-malarial treatment. The longer-term stability of the specific humoral response was evaluated indirectly by determining the antibody titers in the sera from healthy individuals who lived an area from which malaria had been eradicated (450 persons) and an area in which it had recurred (1,524 persons). There were considerable residual antibody responses to PvMSP1c in over 15% of sera from healthy individuals, but only those who had lived in the era when malaria was prevalent. This means that antibodies against PvMSP1c may persist for more than 30 years, the malaria-free duration. This long-term memory of humoral immunity supports the C-terminal region of merozoite surface protein 1 as an effective malaria vaccine, in addition to the neutralizing activity reported previously.