How and when will we get to a Zika vaccine?

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President Barack Obama is asking Congress for $1.8 billion in emergency funding that would in part fund an expedited effort to develop a Zika vaccine, but even with presidential power and funding, a vaccine could still be awhile.

Vaccine development is a slow and deliberate process in large part because it needs to keep test subjects, and ultimately those who will get the vaccine, safe. That wasn’t always the case.

In the 1940s and ’50s, scientists tested the first polio vaccines on themselves and on institutionalized children. Peter Salk even tried his early version of the vaccine on his wife and children. Those trials went well, but the U.S. government suspended a 1955 trial after 11 test subjects died and hundreds were left paralyzed.

Today, vaccines must meet many more government benchmarks before drug makers bring it to market. It takes several years of lab research for scientists to figure out what the antigen is to stop a disease.

Continuing coverage of the Zika virus here

Once the U.S. Food and Drug Administration signs off on the early vaccine material to be tested further, it goes through at least three more stages of testing to determine how big a dose is needed, to see what the side effects are and to see whether it works on a large group of people. Even when governments expedite trials such as in the case of the most recent Ebola outbreak, those tests, while successful, are still ongoing while the worst of the epidemic is already over in West Africa.

Oxitec -- a subsidiary of the biotech firm Intrexon -- is working to control the mosquito-borne Zika virus outbreak in Brazil with its genetically modified mosquitoes. Rafela Santos is seen here holding her son Luiz Felipe. Her son was born with microcephaly. (Miguel Castro/CNN)

Oxitec — a subsidiary of the biotech firm Intrexon — is working to control the mosquito-borne Zika virus outbreak in Brazil with its genetically modified mosquitoes. Rafela Santos is seen here holding her son Luiz Felipe. Her son was born with microcephaly. (Miguel Castro/CNN)

In the case of Zika, it is unlikely the epidemic will be over any time soon. As the virus is “spreading explosively” according to World Health Organization scientists who predict there will be 3 to 4 million new infections in the Americas this year, including in the southern United States.

Unlike with Ebola, which has one of the highest fatality rates of any known pathogenic virus, 80% of people infected Zika show no symptoms.

Zika’s danger seems confined to pregnant women whose unborn babies may be at risk for a severe birth defect called microcephaly. Scientists are also investigating a possible link between Zika and Gullian-Barre, a neurological disease. But scientists have not conclusively tied either to Zika. Brazil, a country with half a million to 1.5 million Zika infections as of 2015, has seen the number of microcephaly cases go up to 3,500, with 46 deaths in the past four months. In 2014, there were only 147 microcephaly cases.

Not knowing much about the disease will slow vaccine development down. Up until recently, Zika was considered rare and relatively benign. It wasn’t until 2007 when there was a large outbreak on Yap Island in Micronesia that it got much attention.

There have only been about 250 scientific journal articles published on Zika, according to data from the National Center for Biotechnology Information. For a disease such as dengue, a virus that’s in the same Flavivridae family, scientists know a lot. There are more than 19,000 scientific papers, and yet the vaccine for dengue was just approved in December. The French company that made that vaccine worked on it for at least 20 years.

Sanofi Pasteur said it hopes to use what it learned in those dengue trials to speed up their hunt for a Zika vaccine, but a “typical vaccine takes about 10 years to develop,” said Nicholas Jackson, who head up the effort. “We have a jump start here because we have experts in-house, technologies in-house; we have an infrastructure that we put in place around dengue vaccine we can tap into very quickly which will hopefully take off (time from) the typical timeline.”

With WHO declaring Zika a public health emergency, it can help the company “galvanize resources and investment” to hurry development, according to Jackson. But the challenges “are considerable.”

“We know very little about the biology of this virus,” Jackson said. Scientists have to answer basic questions such as the rate it spreads, what the clinical complications may be and how to even distinguish it from other viruses.

With past successful vaccine trials, scientists had decades more worth of research. For instance, scientists first figured out polio was a contagious virus in 1908. The first polio vaccine trials began in 1935 and took until 1955 to find one that was viable. Zika wasn’t identified until 1947 and then scientists only saw infections in monkeys. It wasn’t until a decade later that doctors spotted it in humans, but at the time, there was no urgency to develop a vaccine since infected humans only showed mild symptoms and only 20% of the time.

With the high rate of infection in Brazil, the Butantan Institute in San Paulo, along with two other labs connected to the Brazil ministry, will collaborate with companies to find a vaccine. Protein Sciences, a Connecticut biopharmaceutical company, said it is working with Brazilian partners to leverage technology it used creating a flu vaccine to work on Zika.

Company President and CEO Manon Cox thinks her company could have something in human trials in six to eight weeks, but the clinical process “can take maybe three to five years.” Iowa-based NewLink Genetics Corporation, which had worked on an Ebola vaccine candidate, is using that experience to work on a Zika vaccine. And other companies may get into the mix.

The U.S. government also said it is working on two approaches, according to Dr. Anthony Fauci, director of the National Institutes of Allergy and Infectious Diseases. One is a DNA-based vaccine involving a newer technique that injects a piece of the viral DNA rather than a protein fragment of the virus to stimulate immunity in the person’s cells.

The other is what’s known as a “live attenuated” approach, which uses a version of the living virus that is weakened in the lab so it won’t make you sick. But even if Congress approves the extra funding, Fauci doesn’t believe your doctor will give you a Zika vaccine anytime soon either. At a White House briefing Monday he said a vaccine is “unlikely to be widely available for a few years.”

“We can predict that we would likely be in Phase One trial just to determine if it’s safe and if it induces a good response probably by the end of the summer,” he said. “If it looks like it’s safe, we’ll go to the next stage.”