A promising Clostridium difficile (C. diff) vaccine performed well in initial tests and now has moved into a large Phase III clinical program called Cdiffense to evaluate the safety and efficacy of the vaccine for the prevention of C. diff infection.

The hopes have been that this antibiotic-resistant infection can be prevented in long-term care facilities and other settings where it has become a deadly scourge.

The first two phases of vaccine testing involved about 650 volunteers between 40 and 75 years old, who were at risk of C. difficile due to impending long-term care admission or hospitalization. Phase I included high-dose and low-dose versions and the high-dose formulation moved on to the second phase. Phase II participants responded best when vaccinated on day 0, 7 and 30 of the trial, with elderly recipients experiencing particularly strong immune responses. This trial saw significant increase in antibody production against C. diff toxins, across all dosing schedules and volunteer ages.

The testing in Phase III, which began in August 2013 could involve 200 sites in 17 countries. The vaccine so far has proved safe, with the only reactions being mild and of short duration. The C. diff vaccine is meant to work in the same way as tetanus or whooping cough vaccines, by stimulating the immune system to fight C. diff when it appears.