Drug companies are racing to develop a coronavirus vaccine at breakneck speed, but they’re quickly encountering challenges with clinical trials, production capacity and governmental approval.

The world is pinning its hopes on a vaccine to prevent COVID-19, the disease caused by the coronavirus. Public health experts say that until a vaccine is successfully deployed, it will be difficult to completely lift the social distancing restrictions that have devastated the global economy.

Normally, vaccines often take five to 10 years to develop. Limited human trials of some vaccine candidates are already underway, and experts say there is reason for optimism.

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But they also caution that the 12-to-18-month timeline highlighted by federal health officials might need to be extended. They note that the mumps vaccine — considered one of the fastest ever approved — took four years to get from the initial development stages to licensing in 1967.

Probably the biggest hurdle to a coronavirus vaccine is the rigorous clinical trial stage. More than 70 drug companies are working on a potential vaccine, and the majority are unlikely to make it through that process.

Some firms have already launched human trials with new technology that has allowed them to use RNA or DNA sequencing to develop vaccine contenders faster than ever before.

However, that technology is unproven. No RNA or DNA vaccine has ever been approved for a virus, and there aren’t any drug manufacturers working to produce those types of vaccines.

Moderna, which launched the first clinical trial of a potential COVID-19 vaccine in mid-March, told Bloomberg Businessweek it has the ability to produce millions of doses of bulk vaccine per month.

But hundreds of millions of doses, at minimum, will be required to to prevent the disease across the entire country, said Jesse Goodman, a professor at Georgetown University School of Medicine.

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"The challenge is that some of these new technologies have never yet been translated into approved vaccines ... and they haven't been produced at industrial scale," said Goodman, who spent more than 15 years at the Food and Drug Administration and served as chief scientist under former President Obama.

Even if a vaccine can be developed quickly, it will require extensive testing to ensure it is safe for widespread human use.

"The time when [companies] are looking to ramp up manufacturing and have capacity ... is not insignificant," Goodman said.

Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, said even under the most optimistic timeline, the steps for evaluating safety and effectiveness can't be rushed.

"You're going to need time to show, one, that the vaccine actually works ... and, secondly, that it's safe. And it's hard to accelerate that," Hotez said.

Companies are looking to speed the development of a vaccine through condensing trials, conducting multiple trials simultaneously or even intentionally infecting people with the virus.

Hotez, who is part of a team working on a potential vaccine candidate, predicted a bottleneck in the clinical trial process.

"The problem is not making the vaccine. ... The problem is you need the time to show the vaccine works and is safe" and then make sure there's a process in place to manufacture it in large quantities, Hotez said.

If a vaccine nears the finish line, there will be enormous pressure on the federal government to quickly approve it.

Goodman said he hopes companies can produce a vaccine that is at least 80 percent effective. In contrast, the annual flu vaccine ranges from 40 percent to 60 percent in effectiveness.

"But if we didn't ... and if the disease were still actively circulating, a vaccine with lower efficacy could get approved," he added.

Hitting that 80 percent mark in a year for an injectable drug with no side effects is a “fantasy,” according to one drug industry consultant.

"It would be completely different than the entire history of pharmaceuticals, since the development of penicillin, that you have a product exceptionally high in efficacy and very low side effects. ... That's not the way drugs get made," said Jeff Myers, a senior vice president at Catalyst Healthcare Consulting.

"I think the first drug out of the chute is not going to be a magic bullet; it's going to be a start," Myers said. "But you're more likely to get products that can treat symptoms way faster than you're going to get a vaccine."