If you are intended to develop a protein based-vaccine to prevent the disease from occur then you could do an analysis of the antigens of the stages of the trematode that can be found in the definitive host and select a candidate or a mixture of them (specially of the cercarie and immature stages). Antigenic variation between stages in trematodes (and other parasites) is common so you have to use antigens that are expressed in several of these stages and study them regarding their roles in stimulating the host immunity. Assays using cultures of human cells involved in the adaptive response would be useful in this characterization and in the selection of a proper antigen. Then, cultures of the mammalian cells previously activated with the different antigenic candidate (s) can be challenged with cercariae or ideally with schistosomules, to determine the in vitro efficacy of the preparation. The cercariae would be an appropriate target since the aimed of a preventive vaccine is precisely to prevent the successful establishment and colonization of the host by the pathogen and are easily obtained from experimental infections of the snail hosts. Once you have a candidate(s) ready to be tested then you have to prove its efficacy in an in vivo model using immunized animals (mice are commonly used and have been reported to host several schistosomes in experimental infections) and infecting them with the parasite cercariae to assess the progression of the infection and the efficacy of the vaccine formulation.

I hope this could help you. Good luck.

Thanks Annia for your detailed answer

A friend of mine has published a review article on schisto vaccines recently and you can have a brief look on the paper. you can get some details.

good luck!

 https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-016-1799-4