Described are vaccines against malarial infections, which are based on recombinant viral vectors, such as alpha viruses, adenoviruses, or vaccinia viruses. The recombinant viral-based vaccines can be used to immunize against different Plasmodium infections, such as infections by P. falciparum or P. yoelii. Codon-optimized circumsporozoite genes are disclosed. Replication-defective adenoviruses may be used, derived from serotypes that encounter low titers of neutralizing antibodies. Also described is the use of different adenoviral serotypes that are administered to elicit a strong immune response, either in single vaccination set-ups or in prime-boost set-ups in which compositions based on different serotypes can be applied.