Objective To find out a quick,simple and convenient method of determining the viability of Oncomelania hupen-sis. Methods O. hupensis snails were stained for 30 minutes by 0.05%water soluble dye neutral red,0.5%methylene blue,red ink,methylene blue-eosin-borax(MEB)and 0.4%trypan blue,respectively. The soft tissue samples of the snails were observed by a stereoscopic microscope after crushing their shells. Results The vital snails were stained and the dead were unstained in the neutral red. The vital and dead snails were unstained in methylene blue. However,the vital and dead snails were stained in red ink. The partial vital and dead snails were stained in MEB. The vital snails were stained and the partial dead were stained in trypan blue. Conclusion The use of 0.05%water soluble dye neutral red is simple,rapid and accurate in determination of the viability of O. hupensis.

ObjectiveTo determine the serum antibody level and risk factors in the adolescent population in a county in Zhejiang Province， following the immunization with inactivated COVID-19 vaccine， and to construct a prediction model for antibody concentration. MethodsWe conducted the study in a county in Zhejiang Province， employing a stratified cluster random sampling strategy in school children who had received the inactivated COVID-19 vaccine. Data on gender， age， type of vaccine， and time of vaccination was collected. Serum samples were also collected to test for anti-S and N IgG antibody against the SARS-CoV-2 by using chemiluminescent immunoassay （CLIA）. Risk factors were determined to construct a prediction model for antibody concentration. ResultsThe IgG antibody concentration was significantly higher in girls， those who received two doses， and those who had simply received the KX vaccine . It decreased with age and time interval between the sampling and last vaccination. The prediction model constructed by random forest regression in the study had a better model fit and predictive ability than that by the multivariable linear stepwise regression. ConclusionGender， age， vaccination dose， type of vaccine， and time of vaccination are associated with vaccination effectiveness of inactivated COVID-19 vaccines in adolescents. Prediction model could predict the antibody level in the vaccinated population， which can provide a new tool for better evaluation of vaccination effectiveness against emerging infectious diseases in future.