Clostridium difficile, a major cau
se of no
socomial and antibiotic-a
ssociated diarrhea, carrie
s a
significant di
sea
se and co
st burden. Thi
s study aimed to
select an optimal formulation and
schedule for a candidate toxoid vaccine again
st
C. difficile toxin
s A and B.
sSec_2">Methods
spar0010">Randomized, placebo-controlled, two-stage, Phase 2 study in a total of 661 adults aged 40–75 years. Stage I: low (50 μg antigen) or high (100 μg antigen) dose with or without aluminum hydroxide (AlOH) adjuvant, or placebo, administered on Days 0–7–30. Stage II: Days 0–7–30, 0–7–180, and 0–30–180, using the formulation selected in Stage I through a decision tree defined a priori and based principally on a bootstrap ranking approach. Administration was intramuscular. Blood samples were obtained on Days 0, 7, 14, 30, 60 (Stage I and II), 180, and 210 (Stage II); IgG to toxins A and B was measured by ELISA and in vitro functional activity was measured by toxin neutralizing assay (TNA). Safety data were collected using diary cards.
sSec_3">Results
spar0015">In Stage I the composite immune response against toxins A and B (percentage of participants who seroconverted for both toxins) was highest in the high dose + adjuvant group (97% and 92% for Toxins A and B, respectively) and was chosen for Stage II. In Stage II the immune response profile for this formulation through Day 180 given on Days 0–7–30 ranked above the other two administration schedules. There were no safety issues.
sSec_4">Conclusions
spar0020">The high dose + adjuvant (100 μg antigen + AlOH) formulation administered at 0–7–30 days elicited the best immune response profile, including functional antibody responses, through Day 180 and was selected for use in subsequent clinical trials.
