Conjugates of ookinete surface protein Pfs25 are provided that are efficacious as vaccines against Plasmodium falciparum, the most severe form of malaria. Conjugates of ookinete surface protein Pvs25 for use as a vaccine against Plasmodium vivax are also provided. Methods for preparing the conjugates, which comprise the ookinete surface protein bound onto itself or onto another protein by a linking group, are also provided.
