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When public health officials briefed President Barack Obama about the alarming and rapidly evolving Zika virus situation this week, the message that emerged from Washington was clear: The world needs a vaccine.

The same message has emerged from the World Health Organization, which announced Thursday that it would be convening an emergency committee of outside experts to advise it on the extraordinary outbreak “spreading explosively” through the Americas.


“The level of concern is high, as is the level of uncertainty. Questions abound,” WHO’s Director General, Dr. Margaret Chan, announced during a special session on Zika in Geneva. “We need to get some answers quickly.”

But public health experts warn that a vaccine for Zika — which is believed to have caused a surge in cases of babies born with abnormally small brains in Brazil — will be challenging.

As Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy, said: “We’re going to be living for quite a few years in a Zika, vaccine-free world.”


Zika virus, which can be transmitted by mosquitos, has exploded onto the world stage. Alex Hogan/STAT

The challenge is reminiscent of the fight against Ebola. When the virus started ripping through West Africa in 2014, there was no licensed vaccine waiting in warehouses that could be deployed to contain its devastating spread. Vaccines only started to be used in the region in 2015, after the peak of the outbreak, and even then only in clinical trials.

But in the case of Ebola, scientists had been working on vaccines for more than a decade, giving them a foundation to build on. Zika, by contrast, has been virtually ignored by the scientific community, in part because the virus was never seen as a serious, widespread threat to public health.

Zika virus, which has been reported in returning travelers in several US states, including Massachusetts as of Thursday, causes mild, flu-like illness in one out of every five people infected. The rest don’t even know they’re sick.

Experts also note that in the case of any vaccine, developing, testing, and commercializing a product takes years — a process that helps ensure products are safe and effective.

Scott Weaver, the head of the Institute for Human Infections and Immunity at the University of Texas Medical Branch in Galveston, has been designing experimental vaccines to protect against chikungunya virus, which shares some features with Zika virus. He is hopeful that scientists will be able to design a vaccine for Zika using what is known about viruses related to it.

“We can be fairly confident that we can make a good vaccine for Zika fairly quickly,” he said, because scientists have learned how to attenuate, or weaken, similar viruses for the purposes of inclusion in a safe vaccine.

Dr. Anthony Fauci, the director of the National Institute for Allergy and Infectious Diseases — part of the National Institutes of Health — made a bolder prediction. He told STAT this week that an experimental Zika virus vaccine should be ready for Phase 1 testing — the earliest stage of human testing for a vaccine or drug — within this calendar year.

But Phase 1 trials are preliminary and small, designed to show that something is safe enough to continue testing it in people. They don’t tell you whether a vaccine works.

Larger studies known as Phase 2 and Phase 3 trials would have to be designed, conducted, analyzed, and reported before a company intent on licensing the vaccine could apply to the Food and Drug Administration — or some other country’s drug regulatory agency — for approval of the vaccine.

Even if everything goes according to plan, this represents years of work.

One of the world leaders in vaccines, the British company GlaxoSmithKline, has said in a statement that the process for a vaccine normally would take 10 to 15 years. Fauci spoke in expedited terms, but even he admitted: “It might be five or seven years away, a commercial product.”

And to get there on that kind of expedited timeline will take boatloads of money.

Dr. Ernesto Marques, a Zika virus researcher who splits his time between the University of Pittsburgh’s Center for Vaccine Research and Brazil’s FioCruz research institute, said if funders were willing to put up $2 billion — and to provide it all now rather than in chunks over time — he thinks the work could be done in under eight years.

“It’s not going to be three years. That’s impossible.”

The economics of developing a Zika vaccine may also prove challenging.

Because the virus seems to pose the most severe threat to newborns, pregnant women who live in or plan to travel to parts of the world where Zika circulates might race to line up if a vaccine becomes available. Women who want to become pregnant would likely join them in line.

But because most people who are infected with Zika don’t even realize it — and because newly developed vaccines are generally not cheap — the market among people who aren’t women in the childbearing phase of life may not be strong.

Still, Marques thinks that won’t be a problem. He envisages a scenario where girls are given the vaccine before they reach reproductive age — which is the original marketing approach for human papillomavirus or HPV vaccines.

The University of Minnesota’s Osterholm notes there is a long list of recently emerged pathogens that the world would have liked vaccines for, but none have made it to market yet. The list includes severe acute respiratory syndrome, West Nile virus, Ebola, and Middle East respiratory syndrome.

“I think this one is clearly in that same lineup of potential vaccines, but what’s the model for actually bringing it forward in a viable, economic, and scientific way?” said Osterholm, who cochaired an international committee that advised on the work to develop Ebola vaccines.

Osterholm added another complication in the development of any vaccine. Areas with Zika outbreaks have reported an increase in cases of Guillain-Barré syndrome, a neurological disorder that triggers progressive paralysis from the feet up.

Osterholm said it is going to be critical to figure out what is causing the GBS. Is it something about the virus? Or is it brought on by the body’s immune reaction to the Zika infection?

If it’s the latter, there would be concerns that a Zika vaccine might trigger some cases of GBS. It’s an issue that needs to be investigated, Marques said, adding he thinks solutions could be found.

Still, he said, it could add to the time needed to make a vaccine.