RESUMEN
OBJECTIVE:To investigate the long-term toxicity of repeated intramuscular injection of Escherichia coli O157∶H7 polysaccharide-conjugated vaccine(O157) in rats so as to provide safety evidence for clinical trials.METHODS:A total of 48 SD rats were randomly assigned to receive either 0.5 mL vaccine(containing 25 ?g polysaccharides) (immunization group,n=24) or phosphate buffered solution (PBS,control group,n=24) with the same volume for 3 times at a dose interval of two weeks.Sacrifice of 6 rats in each group were scheduled at 2 weeks after first immunization,and at 1,3,and 5 weeks after the third immunization,respectively for observation and determination of hematological and biochemical parameters,histopathology,specific antibody,myeloid tissue,the tissues in injection sites,etc.RESULTS:Compared with control group,immunization group showed no significant pathological change except the dynamic regular change of some hematological parameters induced by the immunization,and no immunologic system damage was observed.CONCLUSION:Repeated intramuscular injection with O157 vaccine in rats wouldn't cause overt toxicity and local irritation.