Pfizer has started enrolling patients into a mid-stage trial of its candidate vaccine for ‘superbug’ methicillin-resistant Staphylococcus aureus (MRSA).
The company is trying to achieve what has eluded vaccine developers for years – finding an effective way to protect patients developing MRSA infections – typically in hospitals – that are becoming increasingly resistant to even last-line antibiotic therapies.
The phase IIb STRIVE trial is being conducted in patients undergoing elective spinal fusion surgery, a massively-invasive procedure that places patients at risk surgical site infections (SSIs) of which one in five are caused by MRSA in the US.
Treating SSIs costs the US healthcare system more than $12bn a year and patients who develop these infections have worse clinical outcomes, including increased mortality in comparison with non-infected patients, according to Pfizer.
While the clinical need is great, efforts to develop an effective MRSA vaccine have yielded only failures, with Merck & Co and Nabi Biopharmaceuticals both abandoning development of candidates after disappointing trials.
Last year, researchers at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center reported that a candidate MRSA vaccine called NDV-3 – being developed by NovaDigm Therapeutics – seemed to block MRSA from invading deeper tissues in animal models of the infection.
NDV-3 is initially being developed for the prevention of vaginal yeast infections and while its immune-stimulating activity also seems to help mitigate S. aureus infections this is a secondary indication for the company. Meanwhile, GSK and Sanofi Pasteur are also working on vaccine candidates but they remain in early-stage development and are not listed in either company’s most recent pipeline updates.
“To date, there is no licensed vaccine available to prevent invasive S. aureus disease,” said Dr. Kathrin Jansen, senior vice president and chief scientific officer of vaccine R&D for Pfizer, which was awarded fast-track status by the FDA for its four-antigen candidate – called SA4Ag or PF-06290510 – in February 2014.
“We believe results from this study, if positive, will bring us closer to a potential preventive measure for this challenging disease that is associated with considerable morbidity and mortality.”
The company says it intends to enrol 2,600 patients into STRIVE who will receive either the vaccine or placebo. The main outcome measure will be the number of subjects in each group developing S. aureus infections in the blood or at the surgical site within 90 days of the surgical procedure.
The study is expected to complete in March 2017.