The U.S. National Institutes of Health (NIH) developed a potential vaccine for West Nile virus, but it failed to find a commercial partner because the virus did not inspire enough public alarm to generate big sales. West Nile leads to serious complications in less than 1 percent of people infected.

In February, the World Health Organization declared a global public health emergency because of Zika’s apparent link to microcephaly, a birth defect marked by small heads and serious developmental problems. That, and evidence of other severe fetal brain abnormalities linked to Zika, have galvanized efforts to speed vaccine development.

The NIH is negotiating with companies to produce Zika vaccines but has its own pilot plant that can make enough for early clinical testing, which began with its first candidate in August.

“We’re not dependent on a company until you prove it works and then you need somebody to manufacture millions of doses,” said Dr. Anthony Fauci, director of the NIH’s National Institute of Allergy and Infectious Diseases (NIAID).

The first NIH candidate is a DNA vaccine containing no actual virus, in which genetically engineered cells produce an antigen that triggers an immune response, similar to the West Nile vaccine. By early 2017, the agency expects to be able to decide whether to begin enrolling thousands of patients in an efficacy study, or move on to the next candidate.

The size of the Zika outbreak may help development efforts. If it remains widespread, it will be easier to tell if a vaccine is effective. “If the infections die down, then it’s going to take much longer to find out if it works,” Fauci said.

A second NIH candidate contains inactivated viral material, while a third utilizes attenuated, or weakened, live virus.

DNA-based candidates are most likely to prove safe, but they typically require multiple doses to work. Vaccines that contain live virus are considered most effective with one dose, but have a far higher safety hurdle, particularly if they are intended for pregnant women, and so they take longer to get to market.

INDUSTRY PILES IN

Inovio’s DNA vaccine is injected along with a brief low voltage electronic pulse that induces cell membranes to open, making them more receptive, in theory, to accepting the vaccine’s genetic material.

Privately-held Protein Sciences Corp built its Zika vaccine using technology similar to its already approved Flublok flu vaccine. The drugmaker has partnerships with companies in Argentina, Brazil, Japan and Mexico and plans to seek funding from Brazil and the NIH. It expects to start human trials by January.