All those advances, though, can’t speed up the time it takes to meticulously monitor how well these candidate vaccines work in people. Clinical trials, a prerequisite for bringing a vaccine to market, are the real bottleneck. Each happens in three stages. Phase 1 involves just a few dozen healthy volunteers, and is meant to evaluate whether the vaccine is safe. That takes about three months. If the healthy volunteers don’t suffer any adverse effects, it’s on to Phase 2. This time, several hundred people will get the shot, ideally in an area experiencing a Covid-19 outbreak, so scientists can gather data on how well it spurs the production of antibodies and fends off the disease for these trial subjects. That’s another six to eight months. If everything still looks good, Phase 3 is to recruit a few thousand people in an outbreak zone and repeat the experiment. That’s another six to eight months—if you don’t have any problems recruiting patients or with your vaccine supply. Then a regulatory agency, like the US Food and Drug Administration, has to review all the data before making a decision about whether to approve the vaccine. That can take months to a year.

If you’ve been doing the math, this means that, since vaccine candidates started being developed in January, a version approved for public use won’t be available until the end of summer 2021, at the earliest. And that’s if nothing goes wrong. “Constricting the whole timeline of going from concept to a product that can be distributed into a year or two is really a herculean endeavor,” Andrus says.

Only a handful of companies have vaccine candidates ready to move into human testing, but more than 30 have joined the race. Even if one of these companies does pull off the Thirteenth Labor, they’re left with a novel product that still requires manufacturing and distribution. “The first question we should be asking is: Does this producer have the capacity to scale it up?” asks Andrus. If not, a limited supply will force public health officials to make tough decisions about rationing out a vaccine.

Isn’t There Any Way to Speed It Up?

In general, these timelines are very difficult to compress. The last thing drugmakers and regulators want is to rush out a subpar product and create—rather than solve—a public health crisis. Making vaccines is so cost-intensive and high risk that most pharmaceutical firms don’t do it anymore. Today, the vaccine business is dominated by just four companies: Pfizer, Merck, GlaxoSmithKline, and Sanofi. Since they’re the ones with the kind of capacity required to fight a global pandemic, they’re the ones that have to be convinced it’ll be worth it.

Covid-19 might seem like a sure bet now. But outbreaks are unpredictable. SARS disappeared just four months after it caused a global panic. The companies that had begun developing vaccines against it had to abandon their trials because there just weren’t enough patients. Similar disease cycles help explain why it took so long to get an Ebola vaccine, which was only approved last December despite dozens of outbreaks since it first emerged in 1976. Plus, government funding and pharmaceutical industry interest tend to evaporate once the sense of emergency fades away. No one wants to make a product that’s not going to be used.

But there are some things governments can do to encourage vaccine makers to take up the challenge despite its riskiness, including providing grants and other financial incentives to spur their involvement. In the US, a division of the Department of Human & Health Services known as the Biomedical Advanced Research and Development Authority often plays the role of incentivizing medical countermeasures against an outbreak. BARDA has so far funded four projects to address Covid-19, including two vaccines, in partnership with Johnson & Johnson and Sanofi. In recent years, an international nonprofit called Coalition for Epidemic Preparedness Innovations, or CEPI, has also raised money to invest in vaccine research. So far, it has committed more than $66 million to vaccine development efforts against Covid-19.