Pfizer Inc. announced that the phase 2 study evaluating the company’s Clostridium difficile (C. difficile) vaccine candidate, PF-06425090, provided positive data, based on a pre-planned interim analysis. The randomized phase 2 study (NCT02561195) examined the safety, tolerability, and immunogenicity of the vaccine in healthy adults 65 to 85 years of age.

Pfizer’s vaccine candidate is designed to help prevent C. difficile infection (CDI), which can include life-threatening diarrhea and pseudomembranous colitis, by inducing a functional antibody response capable of neutralizing the two main disease-causing toxins produced by C. difficile (toxins A and B).

“Despite improved infection control measures, C. difficile disease continues to rise, further augmenting an already urgent public health threat with particular negative impact on older adults,” said Kathrin Jansen, Ph.D., senior vice president and head of vaccine research and development for Pfizer Inc. “We are very encouraged by these interim immunogenicity and safety results demonstrating robust increases in vaccine-elicited neutralizing antibodies to both toxins, that we believe could provide protection against C. difficile disease.”

Based on findings from the pre-planned interim analysis, Pfizer’s C. difficile vaccine candidate will progress into phase 3 in the first half of 2017. Pfizer’s C. difficile vaccine candidate was granted Fast Track designation by the US Food and Drug Administration (FDA) in August 2014. The FDA’s Fast Track designation is designed to facilitate the development and expedite the review of new drugs and vaccines intended to treat or prevent serious conditions and address an unmet medical need.3 About the phase 2 Study The phase 2 study (NCT02561195) was a randomized, placebo-controlled, observer-blinded study of more than 850 healthy adults 65-85 years of age, evaluating the safety, tolerability, and immunogenicity of two dose levels (100 µg and 200 µg) of Pfizer’s C. difficile vaccine candidate on two different three-dose vaccination schedules (Days 1/8/30 and Months 0/1/6).

Clostridium difficile (C. difficile) is a spore-forming pathogen that typically causes symptoms in individuals with altered gut microbial flora, releasing toxins that can result in a range of disease manifestations from asymptomatic colonization to diarrhea, pseudomembranous colitis, toxic megacolon, intestinal perforation, or, in the most severe cases, death. C. difficile, classified by the US Centers for Disease Control and Prevention (CDC) as an urgent public health threat in 2013, is the most common cause of antibiotic-associated diarrhea in the healthcare setting and an increasing concern worldwide.7 Responsible for approximately 453,000 US cases (associated with 29,000 deaths) in 2011, CDI disproportionately affects older adults, with nearly two-thirds of cases in patients over the age of 65.9 Current treatment options may offer temporary therapeutic improvements, but will not provide long-term protection. Up to 25% of patients treated for a first episode of CDI experience a first recurrence of infection, and up to 65% of those patients who experience a first recurrence will experience multiple recurrences.