The race for a Zika vaccine slows, a setback for efforts to head off future outbreaks

The development of a type of Zika vaccine that authorities had hoped to usher to the market has proven more challenging than some scientists and pharmaceutical companies had expected, people involved in the research have told STAT, posing a setback for efforts to avoid future outbreaks of the disease.

Although vaccines typically take years to produce, test, and license, U.S. health officials had voiced confidence that Zika would not be a difficult target, and some predicted that a vaccine could be made and fully tested, ready for Food and Drug Administration assessment, within two to three years. Others predicted a licensed Zika vaccine could be available sometime in 2020.

Even the more cautious forecast now seems optimistic.

Early this month, the vaccine maker Sanofi Pasteur quietly pulled the plug on its Zika vaccine efforts, a reflection of some complications in the development of the vaccine as well as of evaporating market prospects and limited U.S. government funding.

The company said the