C. Diff Vaccine Shows Promise

Oct. 21, 2011 -- A new vaccine shows promise for preventing infection with the potentially dangerous diarrhea bug Clostridium difficile, or C. diff.

In two industry-funded studies of nearly 100 healthy people, the vaccine also proved safe. No serious side effects were associated with its use.

The vaccine targets two toxins, A and B, produced by C. diff that attack the lining of the gut and cause diarrhea, cramping, and other symptoms.

Each year, C. diff strikes about 500,000 Americans, mostly in hospitals and nursing homes. 

The new vaccine, being developed by Sanofi-aventis, is one of several vaccines in early testing.

Ginamarie Foglia, DO, MPH, clinical director at Sanofi-aventis, presented the findings today at the annual meeting of the Infectious Diseases Society of America in Boston.

Early Days of Research

There's a huge need for a vaccine to prevent the disease, Foglia tells WebMD. Althoughdiarrhea is its hallmark symptom, C. diff infection can lead to colitis, perforated colon, and even death.

"We see the vaccine being targeted at high-risk people -- the elderly and those with chronic conditions that increase their chance of being hospitalized and being on antibiotics," she says.

More than 90% of hospital infections with C. diff occur in people who have received antibiotic treatment.

The fact that the vaccine specifically targets the two toxins that cause disease is important, says Kevin Garey, PharmD, MS, of the University of Houston School of Pharmacy. He was not involved with the work.

"If you can mount an antibody response to the two toxins, you [would] predict that you have an effective vaccine," he tells WebMD.

Still, these are the very early days, Garey says. "You’d expect the vaccine to be safe in healthy volunteers. Now they have to prove it is safe in high-risk people," he says.

Antibodies Rise After C. Diff Shot

The new studies involved 48 people aged 18 to 55 and 48 people aged 65 and older. Thirty-six people in each group received one of three doses of the vaccine. The rest got placebo.

Everyone got a C. diff shot at the beginning of the study and boosters one month and two months later.

Among the findings:

• At two months, everyone aged 18 to 55 and older people who got the highest dose showed immunity to toxin A in the form of at least a fourfold increase in C. diff antibodies.

"We used that as a [measure] because up to 60% of Americans have antibodies due to exposure at some point in their lives," Foglia says.

• Also, 75% of the younger adults had at least a fourfold increase in antibodies against toxin B at two months. By two weeks later, 75% of the older adults showed such an increase.
• At eight months, antibody levels against both toxins were higher than at the start of the study, no matter what a person's age or what dose was received. But they were no longer four times higher.
• No one who got placebo had an increase in antibodies at any point in the studies.

C. Diff Vaccine: Moving Forward

One big issue moving forward will be figuring out when to give the vaccine, Garey says. It takes much longer to mount the antibody response than to get the disease, he says.

Although it's too early to know how much the vaccine will cost, a computer model by other researchers showed that a vaccine would be cost-effective for the prevention of C. diff in high-risk patients and also for the prevention of recurrent C. diff, Foglia says.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.