The detection of IgG antibodies against the different SWAP antigenic fractions plus the determination of their avidity in avidity immunoblotting assay using 6 M urea wash, presents a novel alternative for the characterization of optimal antigenic markers for acute and chronic phases of Schistosoma mansoni infection and for vaccine development. Human serum samples from 25 acute schistosomiasis patients, 20 chronic cases and 15 normal healthy controls were analysed by IgG avidity enzyme linked immunosorbent assay (ELISA) and IgG avidity immunoblotting assay. Using avidity ELISA, a pronounced overlap of avidity index values was observed between acute and chronic infections with a range of uncertainty (0.86-1) which was encountered in both groups. Using avidity immunoblotting assay, antigenic bands at >116, 84, 48, 40 & 34 KDa were exclusive for the acute phase. From these bands, 34 KDa was recognized mostly by low-avidity antibodies and showed a high sensitivity (96%) and specificity (100%) making it an optimal marker for the acute phase. 40 KDa band was recognized mostly by high-avidity antibodies even during acute infection. Bands of 80, 70, 42, 36, 30 & 26 KDa were exclusive for the chronic phase. Only 70 KDa band was recognized by high-avidity antibodies yet, with low sensitivity (35%), that limits its use as an optimal marker for the chronic infection. Meanwhile, 70 and 40 KDa bands, recognized by high-avidity antibodies, are considered as potential vaccine antigen candidates.