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Table 1 Acquired immunity, persistence of gametocytes, and transmission.

From: Malaria vaccines and their potential role in the elimination of malaria

1. Acquired immunity to asexual blood stages increases with exposure but allows the persistence of low level parasitaemias from which gametocytes develop.
2. Anti-parasitic immunity will persist after interruption of transmission and may allow the occurrence of asymptomatic infections and hence gametocytaemias for a number of years.
3. Transmission-blocking immunity to gametocytes develops rapidly then wanes so that adults carrying small numbers of gametocytes are less likely to have antibodies that render them non-infective.
4. Low levels of transmission-blocking antibodies have been shown to enhance transmission.
5. The gametocyte reservoir is much larger than that determined by blood film examination even in areas where transmission is low. Transmission of infection can occur from individuals with very low numbers of gametocytes.
6. Gametocyte infectivity is broadly related to gametocyte density but small numbers of infectious gametocytes in adults are as important in maintaining transmission as larger numbers of gametocytes in children susceptible to clinical attacks of malaria.
7. A vaccine for elimination of malaria must ensure everyone susceptible to malaria infection is protected completely or that all gametocytes are made non-infective.