biostudies-literatureLivingstone MRural and Environment Science and Analytical ServicesScottish Government RuralAnalytical ServicesEnvironment Science89https://www.ebi.ac.uk/biostudies/studies/S-EPMC11768554biostudies-literatureUnknown13(1)<h4>Background/objective</h4><i>Chlamydia abortus</i>, the cause of ovine enzootic abortion, is a zoonotic bacterial pathogen and one of the most infectious causes of foetal death in sheep worldwide. Although the disease can be controlled using commercial inactivated and live whole-organism vaccines, there are issues with both, particularly concerning efficacy and safety. Recently, we have described the development of a new COMC (chlamydial outer membrane complex) vaccine based on a detergent-extracted outer membrane protein preparation of the pathogen, which can be delivered in a single inoculation and is both efficacious and safe.<h4>Methods</h4>In this study, we have evaluated the COMC vaccine further in a dose-response titration of the chlamydial antigen content of the vaccine (from 20VaccinesProtective Efficacy of Decreasing Antigen Doses of a <i>Chlamydia abortus</i> Subcellular Vaccine Against Ovine Enzootic Abortion in a Pregnant Sheep Challenge Model.PMC11768554not applicableAitchison KPalarea-Albaladejo JPaladino ALivingstone MChianini FCiampi FLongbottom DEntrican GUnderwood CWattegedera SRfalseProtective Efficacy of Decreasing Antigen Doses of a <i>Chlamydia abortus</i> Subcellular Vaccine Against Ovine Enzootic Abortion in a Pregnant Sheep Challenge Model.<h4>Background/objective</h4><i>Chlamydia abortus</i>, the cause of ovine enzootic abortion, is a zoonotic bacterial pathogen and one of the most infectious causes of foetal death in sheep worldwide. Although the disease can be controlled using commercial inactivated and live whole-organism vaccines, there are issues with both, particularly concerning efficacy and safety. Recently, we have described the development of a new COMC (chlamydial outer membrane complex) vaccine based on a detergent-extracted outer membrane protein preparation of the pathogen, which can be delivered in a single inoculation and is both efficacious and safe.<h4>Methods</h4>In this study, we have evaluated the COMC vaccine further in a dose-response titration of the chlamydial antigen content of the vaccine (from 202025-01-01T00:00:00Z2025 Jan2026-04-08T19:49:01.505Z2025-04-06T07:45:54.24ZS-EPMC117685543985286910.3390/vaccines13010089