After a phase 3 flop, Sanofi cans its C. diff vaccine hopes

Already reeling from bad news on its dengue vaccine, Sanofi canned its phase 3 C. difficile candidate—and the $500 million-plus in sales that might have come with it.

Citing results from an interim trial analysis, Sanofi ended development on its C. diff candidate after an Independent Data Monitoring Committee found the probability for success going forward would be low, the company said Friday.

C. diff usually spreads through hospitals and other healthcare facilities, and a vaccine has become an increasing priority for the scientific community as antibiotic-resistant bacteria continue to threaten. 

Chasing Sanofi, Pfizer earlier this year reached phase 3 with its C. diff vaccine, PF-06425090. Credit Suisse analysts previously predicted Sanofi's vaccine could reel in $525 million in 2020, with Pfizer's candidate pegged at $450 million. 

RELATED: Philippines halts Sanofi Dengvaxia vaccination program, launches probe into officials’ conduct 

For Sanofi, the C. diff news comes right on the heels of another problem: a new safety warning on Dengvaxia that quickly erupted into an investigation in the Philippines. An official there recently called the country's $70 million vaccination program—the first globally for Dengvaxia—a "shameless public health scam" that put lives at risk. The country promised to "leave no stone unturned" in finding out what had happened. 

Last week, Sanofi warned that its vaccine can cause more serious infections if used in patients who've never before been infected with dengue. With dengue, a second infection is typically much worse than the first, and the vaccine itself can act as a natural first infection for those who haven't had prior exposure.  

Then, if a vaccinated person encounters the virus naturally, they could contract a more severe infection. Sanofi said its vaccine can still help those who have already been exposed to dengue. The warning arose from a new analysis of long-term clinical trial data.

RELATED: Chasing Sanofi, Pfizer tees up phase 3 trials for C. diff vaccine 

As a result of the new analysis, the company has asked regulators to curtail the shot's target population, and it's taking a related €100 charge against earnings in the fourth quarter. Sanofi spent $1.5 billion and 20 years developing Dengvaxia and has yet to generate meaningful sales. 

Now, the C. diff project won't have its chance to bear sales fruit, either. And both setbacks follow a separate vaccine pricing and licensing controversy for Sanofi in Zika that started late last year and continued into the summer of 2017. Then, back in September, Sanofi pulled the plug on its Zika vaccine project in conjunction with the U.S. government after federal officials canceled much of its funding. 

In doing so, the government cited a decline in Zika prevalence for "de-scoping" the project. But before that, critics had blasted the company for not issuing pricing commitments on a product that taxpayers would have helped develop. The issue generated months of headlines and drew attention from some top lawmakers.