• Vaccine Name: EcSf2a-2
• Target Pathogen: Shigella
• Target Disease: Shigellosis
• Vaccine Ontology ID: VO_0000670
• Type: Recombinant vector vaccine
• Antigen: This vaccine is an aro-D mutant derivative of EcSf2a-1 (Kotloff et al., 1992).
• Preparation: The vaccine was suspended in 20 ml of BHI broth and contained 1.5 x 10^11 CFU of bacteria (Kotloff et al., 1992).
• Virulence: Vaccinated monkeys were protected against shigellosis after challenge with S. flexneri 2a (Kotloff et al., 1992).

Human Response

• Vaccination Protocol: 19 volunteers ingested three doses of either ca. 5.0 x 10^6, 5.0 x 10^7, or 2.0 x 10^9 CFU of bacteria (Kotloff et al., 1992).
• Persistence: All 46 vaccine recipients excreted the vaccine strain on at least one occasion. Recipients of three spaced doses of ca. 2.0 x 10^9 CFU shed ca. 10^5 organisms per gram of stool for an average of 7 days. Duodenal colonization was detected in five subjects, all recipients of ca. 2.0 x 10^9 CFU (Kotloff et al., 1992).
• Immune Response: A fourfold increase in IgA or IgG antibody titers recognizing purified LPS was detected in 61% of those tested, and a seroresponse to IPA was detected in 44% of the 38 recipients of ca. 2.0 x 10^9 CFU. The IgM response was meager. Circulating IgA ASC specific for S. flexneri 2a LPS and for IPA were each detected in 97% and 60%, respectively, of the 30 subjects tested (Kotloff et al., 1992).
• Side Effects: Diarrhea, dysentery, and fever were observed in vaccine recipients (Kotloff et al., 1992).
• Challenge Protocol: Challenge doses of 1.6 x 10^9 and 1.8 x 10^9 CFU of ECSf2a-2 were given to the volunteers (Kotloff et al., 1992) .
• Efficacy: Vaccine efficacy was only 9% in the challenge study, in which 30% of recipients of three doses of ca. 2.0 x 10^9 CFU developed illness, compared 33% of 9 unvaccinated control subjects. Overall, the vaccine efficacy was 36%. Neither class-specific titers in prechallenge sera nor fourfold rises in antibody titer after vaccination could be correlated with protection against challenge (Kotloff et al., 1992).