Acambis: C. difficile vaccine elicits antibody responses in phase 1 study

By E. Janene Geiss

Philadelphia, Feb. 15 - Acambis plc said Wednesday that results from a phase 1 trial of its investigational vaccine against Clostridium difficile in healthy adults showed antibody responses in all subjects who received the vaccine.

Four weeks after the first injection of the highest dose, anti-toxin A and anti-toxin B immunoglobulin G levels were at least 10-fold higher than those reported in another study of patients who had recovered from natural infection with C. difficile and did not suffer recurrent disease, according to a company news release.

Future efficacy trials will investigate the antibody levels produced by the vaccine that are needed for clinical protection against C. difficile-associated disease (CDAD), officials said.

C. difficile infection is the leading cause of antibiotic-associated diarrhea in hospitals. Most CDAD cases involve elderly individuals who become infected in hospitals and long-term care facilities that have become reservoirs of these bacteria, officials said.

It is estimated that C. difficile causes at least 350,000 cases in the United States alone with annual costs to the health care system exceeding $1 billion, officials said.

Recently, researchers from Canada, the United Kingdom and the United States have reported markedly increased rates of CDAD and more serious disease. In a recent outbreak in Quebec caused by a new epidemic strain, the mortality attributable to C. difficile was 16.7%, officials said.

The company's trial evaluated the safety, tolerability and immunogenicity of its C. difficile vaccine when administered at different dose levels. The randomized, double-blind, placebo-controlled study included a total of 50 healthy adult subjects: 37 subjects received the vaccine and a control group of 13 subjects received a placebo, officials said.

Vaccination at all dose levels was well tolerated in all subjects. The majority of side effects observed were those typical of vaccines injected intramuscularly. These reactions included mild tenderness, redness and pain at the injection site and headache. No subjects experienced unexpected or serious vaccine-related adverse events, officials said.

"The need for a vaccine to protect against C. difficile infection has grown with the emergence of a hypertoxic and epidemic C. difficile strain associated with severe disease, which has been reported in North America and the U.K. These results are encouraging and show that subjects vaccinated with our C. difficile vaccine developed high levels of antibodies against toxins A and B, the toxins responsible for CDAD," Thomas Monath, chief scientific officer of Acambis, said in the release.

As previously announced, a second phase 1 trial of the company's vaccine is underway in healthy elderly adults with results expected later this year.

Phase 2 proof-of-principle trials are scheduled to begin before the end of the year, officials said.

Acambis, based in Cambridge, England, and Cambridge, Mass., is a leading developer of vaccines to prevent and treat infectious diseases.

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