A century after the 1918 flu outbreak, experts question if we’re ready for the next crisis.

This year, the seasonal flu is taking a heavy toll in the United States, with widespread infections in nearly all states. Some hospitals are so overloaded they’re treating people in parking lots.

But this flu season remains dwarfed by the 1918 influenza pandemic that infected one-third of the world’s population exactly one century ago.

Despite medical breakthroughs over the past 100 years, experts remain concerned that the United States is ill-prepared for another influenza pandemic.

While the seasonal flu afflicts Americans every year, an influenza pandemic is different.

This type of pandemic is the result of a new influenza virus being introduced into the human population.

Since it’s a new virus, the human immune systems may have no antibodies to fight the disease effectively. As a result, it can spread quickly across the entire globe and cause widespread deaths in a matter of weeks.

In 1918, among the worst pandemics ever recorded, about 500 million people were infected. There were around 50 million estimated deaths.

In the West, “The 1918 pandemic killed as many children aged 1 to 4 as today die of all causes over a 20-year period,”John Barry, author of “The Great Influenza: The Story of the Deadliest Pandemic in History,” said during a Smithsonian forum called “The Next Pandemic: Are We Prepared?” last November.

Barry said most of the deaths from the 1918 flu happened within just 10 weeks of the virus spreading.

In many ways, the U.S. health system is far more prepared to handle an influenza outbreak today than in 1918.

There was no vaccine to fight the 1918 flu or antivirals like Tamiflu to mitigate symptoms. In fact, many believed the flu was caused by bacteria.

No antibiotics were available to help with secondary infections that can be brought on by the viral disease weakening the immune system.

Today, there are better medications available, and a global system set up by institutions like the World Health Organization to monitor for new, potentially deadly viruses like the bird flu.

The U.S. Department of Health and Human Services (HHS) has a Pandemic Influenza Plan to provide a roadmap for how the country could respond to a major outbreak.

However, experts warn there are many ways that a truly deadly pandemic could still strain or overwhelm the health system.

The HHS estimates that even a moderate pandemic might result in the hospitalization of 800,000 Americans with 160,000 ending up in the ICU. In a severe pandemic, that number could reach into the millions.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, said many hospitals are designed to operate at capacity. This means an influx of patients could be overwhelming.

“In urban areas, our hospitals are essentially full on a daily basis,” he explained. “That is because it costs so much money to build and staff a healthcare facility, so we have been very careful about not overbuilding.”

However, in the event of a pandemic, Schaffner said it’ll be difficult for hospitals to handle dozens to hundreds of extra patients.

Even if places like schools or stadiums are used to add more treatment beds, Schaffner said there aren’t many extra nurses and physicians to treat new patients.

“We haven’t built any surge capacity in healthcare facilities,” he said. “We don’t have a small army of trained nurses to treat patients” that we can call up, he added.

While the antiviral medication Tamiflu has been stockpiled, Schaffner pointed out that other key ways of treating severe flu cases, like ventilators, could start to run out in a severe pandemic.

A 2017 study estimated that a severe pandemic can lead to a 36-fold increase in hospitalizations for infected patients. The study’s researchers estimated Texas would have to stockpile more than 10,000 extra ventilators to help treat patients during a severe pandemic.

Even IV bags could be impacted. This year, after Hurricane Maria damaged key IV bag suppliers in Puerto Rico, hospitals throughout the nation have been dealing with an IV bag shortage during the normal flu season.

In 2009, the swine flu pandemic quickly spread across the globe after being detected in the spring.

Officials at the Centers for Disease Control and Prevention (CDC) pushed to get a vaccine into production in order to vaccinate those at risk by the next winter in hopes of reaching people before the virus peaked.

But the swine flu outbreak peaked in September, about one month before the fast-tracked vaccine became widely available, according to Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases.

“The percent of illnesses peaked before the vaccine was available,” Fauci said at the Smithsonian forum on pandemics.

He said that despite the government’s best vaccine production efforts, there’s often little they can do to outrun a pandemic.

“Even though we have some warning about a pandemic, even then with our current capabilities, it doesn’t work well,” he said.

Fauci said that in order to save lives, more money and research needs to be spent on developing a universal flu vaccine.

“A hundred years after the lethal 1918 flu, we are still vulnerable,” Fauci said at the forum. “Public health infrastructure has improved greatly, but without a universal vaccine, a single virus could result in a world catastrophe.”

Schaffner also said that new technologies — including creating vaccines in cells rather than eggs — may help increase the speed to create a vaccine.

However, he said some steps in a vaccine production process can’t be sped up, pointing out that it’ll take weeks to see if a vaccine works in a human — no matter if it’s egg-based or cell-based.

“Sometimes we can reduce the time it takes to go through the various steps, but some of them are pretty fixed,” he said.

One problem with preparing for pandemics of the future is figuring out who’s going to pay for it.

Dr. Stephen Morse, professor of epidemiology at the Columbia University Medical Center and the Columbia University Mailman School of Public Health, said part of the problem is the public pressure on politicians can lessen when there’s not a current threat.

“With bad news, there’s a certain degree of probably overload or fatigue on the part of the public — they’ve heard about several outbreaks now,” he said.

Dr. Jonathan Quick, author of “The End of Epidemics: The Looming Threat to Humanity and How to Stop It,” said in an editorial published in Time that relatively little funding is currently dedicated to finding a universal flu vaccine.

“Annual funding to find a universal vaccine has never approached even $100 million a year, even as the seasonal flu has cost the U.S. economy an estimated $87 billion a year,” he wrote.

Even at the height of the Zika virus, funding for the National Institutes of Health (NIH) to fight the disease wasn’t guaranteed.

Unlike FEMA, which has an emergency disaster relief fund waiting, there’s no such fund for public health disasters.

It took seven months for Congress to ultimately approve $1.1 billion to combat the Zika virus — far less than the $1.9 billion initially requested by the White House.

During that seven-month gap, the CDC and NIH had to reorganize their funds in order to research and study potential Zika vaccines.