BACKGROUND: Malaria transmission depends on the presence of gametocytes in the peripheral blood of infected human hosts. Understanding malaria infectious reservoirs enables transmission-blocking interventions to target the most important hosts for the disease. This study characterized the distribution of gametocyte carriage as a baseline for the clinical evaluation of a Pfs25-based transmission-blocking vaccine candidate in Bagamoyo, Tanzania. METHODS: A malaria survey was conducted in five locations from May to August 2022. A total of 467 participants-192 children (5-12 years), 65 adolescents (13-17 years) and 210 adults (18-45 years)-were enrolled. Malaria was detected using three methods: rapid diagnostic tests, light microscopy and quantitative polymerase chain reaction. The geometric mean of the gametocyte density, and weighted arithmetic mean of the gametocytes sex ratio were estimated. RESULTS: Overall, 23.5% (110/467) of the participants tested positive for malaria parasites, with the majority of positives (>
92%) being Plasmodium falciparum. The overall gametocytaemia was 5.6%, with a percent positivity of 6.8% (13/192), 6.2% (4/65) and 4.3% (9/210), in children, adolescents, and adults, respectively. The geometric mean gametocyte density (gametocytes/μL) was greater in adults (124.6) than in children (71.7) and adolescents (50.5). Regression analysis revealed that gametocytes were more likely to be present among male participants than among female participants [ORa: 2.79 (95% CI: 1.19 - 6.59) p = 0.019]. The gametocyte sex ratio in children and adult gametocyte carriers was similar but greater than that in adolescents. CONCLUSION: The observed gametocyte densities and distribution across age groups suggest the need for malaria transmission-blocking interventions to target all populations in heterogeneous transmission settings. The implication of targeting only children may leave residual malaria transmission and reinfection from the left-out groups.