Pfizer's C. difficile Vaccine Succeeds in Phase II Study

On January 26, 2017, Pfizer Inc., a global pharmaceutical company, announced that results from a phase II study on a vaccine to prevent Clostridium difficile (C. difficile) infection in adults has provided “positive data.”

According to Kathrin Jansen, PhD, senior vice president and head of Pfizer’s Vaccine Research and Development, “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.”

C. difficile infections have made several headlines during the last few years as an emerging threat against public health, particularly among the older demographic. In 2013 the Centers for Disease Control and Prevention identified C. difficile to be an “urgent public health threat,” since it is “the most common cause of antibiotic-associated diarrhea in the healthcare setting and an increasing concern worldwide.” Consequently, the US Food and Drug Administration granted a Fast Track designation to the vaccine, PF-06425090, in 2014. According to Pfizer, the 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.”

The randomized phase 2 study examined the immunogenicity, safety, and tolerability of the vaccine in 854 healthy adults between the ages of 65 to 85 years. Researchers found the experimental vaccine could potentially inhibit severe diarrhea and pseudomembranous colitis by inducing a functional antibody response that can neutralize the two main disease-causing toxins (toxin A or B) produced by C. difficile.

The study observed two dose levels (100 µg and 200 µg) of the vaccine candidate. Each study participant randomly received three doses of vaccine on one of two vaccine schedules (days 1/8/30 and months 0/1/6).

The primary outcome measures of the study included:

•Proportions of individuals in each vaccine group with toxin A- specific neutralizing antibody level greater than or equal to the specified threshold for toxin A. (Time Frame: 7 days or 1 month after dose 3)

•Proportions of individuals in each vaccine group with toxin B- specific neutralizing antibody level greater than or equal to the specified threshold for toxin B. (Time Frame: 7 days or 1 month after dose 3)

“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 protections against C. difficile disease,” said Dr. Jansen.

Officials have confirmed that based on findings from the pre-planned interim analysis, the PF-06425090 candidate will transition into phase III within the first half of the year.