In the event of a global and highly lethal flu pandemic, we'll need to churn out millions of vaccines as soon as humanly possible. Not easy to do considering a true vaccine can't be developed until the pandemic has already arrived. So it's not surprising the military wants better vaccines that can be produced at blazing speed. Preferably ones it can grow.

The trick is to make lots of flu vaccines by growing tons of vegetables. That's under exploration by researchers who hold $21 million worth of funding from the Pentagon's mad scientists at Darpa – and Darpa has been pursuing veggie-based vaccine research, called Blue Angel, since 2005. This week, Darpa-funded vaccine firm Medicago announced it hit a key goal: producing 10 million doses of a plant-based H1N1 influenza vaccine within a month.

A month might sound like a long time during flu season. But a fast-spreading, lethal contagion is perhaps the most likely kind of mass-casualty disaster humans can face. Remember the 2009 H1N1 influenza? According to a recent Centers for Disease Control and Prevention estimate, the virus killed an estimated 284,500 people worldwide.

If H5N1, another subtype of influenza we know as "bird flu," mutated into an airborne virus, the global mortality rate could reach higher than 60 percent. (By comparison, the last major pandemic in 1918 killed 50 million people with a mortality rate of 2.5 percent.) Your target population for the vaccine? Everyone, according to the World Health Organization (.pdf). That means the 7 billion people of Planet Earth would need to be vaccinated.

"In short, the potential for a pandemic exists and current technological limitations on defensive measures put the health and readiness of U.S. military forces at risk," a DARPA statement announcing Medicago's grow-your-own vaccine achievement reads. "A technological solution to increase the speed and adaptability of vaccine production is urgently needed to match the broad biological threat."

The standard method of creating flu vaccine involves chicken eggs. Seriously: researchers combine the virus with a chicken embryo. But it takes months to ramp up production, and it takes a lot of eggs to cover a population. One estimate has it at nearly a billion eggs just to cover the U.S. alone. That's a billion eggs you might not have during an outbreak.

Plant-based vaccines, however, are developed using "virus-like particles," which consist solely of protein and are non-infectious. They can't spread between people, and they help produce anti-viral antibodies. To produce the particles, scientists synthesize the DNA of the flu virus, combine the flu DNA with bacteria, and then soak the plants with it. After soaking for a few minutes, the plants then start producing the flu-fighting particles. The DNA stays in the plant. The protein is then extracted and becomes the basis for a vaccine.

The most popular plant? Tobacco, as it grows relatively fast. The U.S. is also estimated to produce a heaping 450 metric tons of tobacco per year. And the whole process of turning tobacco into vaccines only takes a matter of weeks to complete. On a large enough scale, plant-based vaccines could be conceivably produced at 100 million vaccines a month. Egg-based vaccines, though, can take months just to develop.

A flu pandemic would also be a new kind of flu, striking a global population without a pre-existing immunity. This means the virus can take more than one dose of vaccine to prevent. But Darpa hopes the plant-based vaccines can be produced strong enough to only require a single dose. The fewer the doses per person, the fewer vaccines you have to produce.

In 2009, the Army expressed fears in an annual summary of its military programs that "High rates of absenteeism [caused by a pandemic] could generate civil unrest, requiring Army action at a time when the Army's own readiness might be degraded." The military could also be called on to help prevent the influenza from spreading, and it won't be able to do that if its troops are incapacitated with the illness.

The military better hurry. And Medicago still has to send the vaccine through clinical trials before it gets FDA approval. While H5N1 hasn't mutated into a form that can spread into humans – outside of a laboratory, that is – the virus has blown away any doubts that it can. All it might take is a chance mutation to make the threat real.