Table 5.

Cross-protection after immunization with an S. flexneri 2a/3a (CVD 1207/CVD 1211) combination vaccinea

ImmunizationChallengeAttack ratebEfficacy (%)PcSeverity scoredPe
SerotypeStrain
Vaccine1a3055-898/15 (53)420.06520.06
Placebo1a3055-898/9 (89)3.4
VaccineY3152-923/12 (25)80<0.0010.5<0.001
PlaceboY3152-929/10 (90)3.6
Vaccine1b3155-966/15 (40)560.0161.30.006
Placebo1b3155-969/10 (90)3.1
Vaccine4b3143-9412/15 (80)200.2242.70.015
Placebo4b3143-949/9 (100)4
Vaccine2b3346-871/15 (7)92<0.0010.2<0.001
Placebo2b3346-878/9 (89)3.4
Vaccine5b5107-824/14 (29)640.0180.90.02
Placebo5b5107-828/10 (80)2.3
Vaccine6CCHO-6010/15 (67)40.6072.50.44
Placebo6CCHO-607/10 (70)2.4
  • a S. flexneri 2a strain CVD 1207 conferred 85% protection against wild-type S. flexneri 2a strain 2457T; S. flexneri 3a strain CVD 1211 conferred 75% protection against wild-type S. flexneri 3a strain J17B.

  • b Number positive in Sereny test/total number tested (percent positive).

  • c Fisher exact test on attack rate, vaccine versus placebo.

  • d Mean of severity score.

  • e Mann-Whitney test on severity score, vaccine versus placebo.