Safety and immunogenicity of Escherichia coli O157O-specific polysaccharide conjugate vaccine in 2-5-year-old children

Background. Escherichia coli O157:H7 causes severe enteritis and hemolytic-uremic syndrome, mostly in young children and older adults. Similar to the case with Shigella, serum IgG against the O-specific polysaccharide of E. coli O157: H7 may confer immunity by lysing the inoculum in the intestine. A phase 1 trial in adults showed that a vaccine of E. coli O157: H7 O-specific polysaccharide conjugated to recombinant exotoxin A of Pseudomonas aeruginosa ( O157-rEPA) was safe and immunogenic. Methods. A phase 2 trial of the O157-rEPA vaccine was conducted in 49 children 2 - 5 years old who were divided randomly into groups receiving 1 or 2 doses of vaccine. Adverse reactions were monitored. Serum IgG lipopolysaccharide ( LPS) antibodies were determined. Results. No significant adverse reactions were observed. At 1 week after the first dose was administered, most children ( 81%) responded with a 14-fold increase in serum IgG LPS antibodies. At 6 weeks after the first dose was administered, all children responded with a 18- fold increase; a second dose did not elicit a booster response. At 26 weeks after the first dose was administered, the geometric mean titer of serum IgG LPS antibodies was similar to 20-fold higher than was the prevaccination titer. These serum samples had high titers of bactericidal activity that were correlated roughly with serum IgG LPS antibody titers (r = .78). Conclusions. The O157-rEPA vaccine was safe and immunogenic in young children. A phase 3 trial of the administration of this conjugate vaccine concurrently with routine immunization in infants is planned.