Companies vying to produce a vaccine for the Zika virus are in a race against time while there's still a large enough population of infected cases to test.
More than a dozen companies are working on a vaccine. The production process, according to the World Health Organization, could take up to 18 months before the drugs now at the most advanced stages of development are ready for large-scale clinical trials.
Development of a vaccine can take up to 10 years to complete and to receive approval. In emergency cases, the government can allow for that process to be expedited. Still, the length of even that process can extend past the life cycle of an epidemic. For a disease that is spreading at the rate of Zika, any effort to test a viable vaccine candidate could be made more difficult as more people become immune to the virus.
Some fear the virus could outpace efforts toward vaccine development much as what happened during outbreaks of the West Nile and Ebola viruses.
Attempts toward producing a West Nile vaccine first began several years after the virus was introduced into the U.S. in 1999. The virus quickly took hold and spread throughout most of the country.
But vaccine production efforts stalled after the virus became native to the U.S. Like Zika, the vast majority of those infected with West Nile never developed symptoms, which lasted between three and 14 days, and usually became immune from subsequent infections.
“That's actually the main reason why we never developed a vaccine for West Nile virus,” said Dr. Gary Nabel, chief science officer for pharmaceutical firm Sanofi, which recently announced plans to develop a Zika vaccine. “It's now very sporadically found, so how do you do a trial that shows that your vaccine works?”
A similar situation arose with efforts to develop an Ebola vaccine. In that case, a viable candidate has yet to be approved despite interest from a number of drug companies that began work on a vaccine. By 2015, clinical trials of a candidate had to be moved from Liberia, one of the hardest hit countries of the epidemic, because the number of cases had dropped too low to conduct testing.
“I think the Ebola epidemic really did illustrate the complexities of rolling out new treatments,” Nabel said. “You're always walking this line between speed and wanting to move something forward that's safe and protective.”
Despite this challenge, Nabel felt there were some positive aspects of vaccine development for Zika. One of which was the drugmaker's experience working on vaccines for viruses that are in the same family as Zika, such as Dengue and Yellow Fever.
“We know it's possible to make vaccines against these types of viruses,” Nabel said.
The urgency to make a vaccine for the Zika virus is gaining momentum as the outbreak spreads. It's now in 31 countries and has been linked to cases of pregnant women giving birth to babies with microcephaly, a condition that causes the head to develop at a much smaller size than normal.
Last week, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told a congressional committee that he expected a Zika vaccine candidate to be ready to enter the first stage of human testing by this fall.
Nabel stressed that the government's involvement in developing new vaccines can make a difference. He said the $1.9 billion in funding proposed by the Obama administration toward combating Zika and financial incentives such as a bill being considered in the Senate to add Zika to the list of rare tropical diseases on the Food and Drug Administration's priority review voucher program are all encouraging increased private investment in vaccine development.