One hundred years ago, death came with astonishing speed and horrifying agony.
Some influenza patients admitted to a Boston hospital in the morning of October 1918 would be dead by the evening, their bodies turning blue from lack of oxygen. Hospitals reported an average 100 deaths a day, overwhelming morgues.
Up to 500 million people — about one-third of the world's population — became infected with the influenza virus, the Centers for Disease Control and Prevention says. As many as 50 million died, or one out of every 30 human beings on the planet, killing more American troops than those that died on the World War I battlefields.
The intensity and speed with which it struck were almost unimaginable, the worst global pandemic in modern history.
Most chilling is that such a calamity could occur today.
"A global influenza pandemic is number 1, 2, 3 and 4 on our list of the most feared public health crises," according to Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy.
Another expert, Vanderbilt University infectious disease specialist William Schaffner, said, "We fear flu. We know how serious it is."
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It could happen again
Top health and science groups, such as the World Health Organization, the National Academy of Sciences, and the Centers for Disease Control and Prediction, predict influenza pandemics are nearly certain to recur.
"Influenza viruses, with the vast silent reservoir in aquatic birds, are impossible to eradicate," the World Health Organization warned. "With the growth of global travel, a pandemic can spread rapidly globally with little time to prepare a public health response."
A pandemic could also arise if a strain mutates with or develops directly from animal flu viruses, the CDC said. The main contributors to a potential pandemic are the lack of a universal vaccine and humans' lack of immunity to those potential unborn strains.
"The threat of a future flu pandemic remains," the CDC said. "A pandemic flu virus could emerge anywhere and spread globally."
If an equal ratio of Americans died in a pandemic today, that would be an unimaginable 2 million Americans. That's the current population of the entire Las Vegas metropolitan area.
In a near worst-case scenario, a new, lethal and highly infectious flu virus would break out in a crowded, unprepared megacity that lacks public health infrastructure, according to Johns Hopkins' Bloomberg School of Public Heath.
Such a fast-moving virus could burst from a city and catch a ride with international travelers before public health officials realize what is happening.
Specifically, avian influenza viruses like H7N9 top pandemic threat lists, according to Johns Hopkins. While these strains are mostly harmless in chickens, they could potentially evolve into much deadlier strains for humans.
"In terms of pandemic potential, an avian influenza virus is thought to be a likely candidate, based on prior pandemics," says Amesh Adalja of the Center for Health Security at the Johns Hopkins Bloomberg School of Public Health.
However, there are safeguards to detect and counteract influenza outbreaks that did not exist 100 years ago.
These include systems to detect signs of potential outbreaks around the world, Schaffner said. In addition, he said scientists have the capacity to make vaccines more rapidly and also have better antiviral drugs that could be used to treat those who contract the disease.
Still, influenza and the potential for a pandemic are concerns that are always at the top of the list for experts who work with infectious diseases and public health, he said.
Pandemics ignore national borders, social class, economic status, and even age.
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1918 pandemic
Spreading from birds to humans, the 1918 pandemic might have started in Kansas. Or France, or maybe Asia, according to Olsterholm.
What is known is that it was caused by an H1N1 virus with genes of bird origin. The First World War, about to come to its horrific end in Europe in November 1918, may have played some role in moving the virus around the world. "But we can't say that the war was the cause," he said.
It was "a widespread, worldwide pandemic. It was a virus no one had ever seen before," said Dr. Paul Offit, director of the vaccine education center at the Children's Hospital of Philadelphia.
The pandemic killed more people in 24 months than AIDS killed in 24 years, more in a year than the Black Death killed in a century, according to the book "The Great Influenza."
The dead included about 675,000 people in the United States. In just the month of October alone, the worst single month in the U.S., an unthinkable 100,000 Americans died. Many were young adults in the prime of their life.
"The high mortality in healthy people, including those in the 20-40 year age group, was a unique feature of this pandemic," the Centers for Disease Control said.
The World Health Organization said the 1918 influenza pandemic was known colloquially as "Spanish flu," although there was nothing "Spanish" about the epidemic.
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Flu today and how to protect against it
Although every flu season is different, and influenza infection can affect people differently, millions of people get the flu every year, according to the CDC. Hundreds of thousands of people are hospitalized and thousands or tens of thousands of people die from flu-related causes every year.
An annual seasonal flu vaccine is the best way to help protect against flu, the CDC said. Everyone 6 months of age and older should get a flu vaccine every season.
Even if it's only 40 percent effective, that's still better odds than doing nothing at all, Offit said. "Influenza knocks you out."
Vaccination has been shown to have many benefits, including reducing the risk of flu illnesses, hospitalizations and even the risk of flu-related death in children. Osterholm recommends getting the shot as close to the heart of flu season as possible, since the duration of protection is limited.
As what a person can do to prevent a future pandemic, though a seasonal vaccine would be ineffective, he said the best action is to reach out to the government and tell them to start working on new vaccines for influenza.
"There are potentially new pandemic strains out there," he said. "But we've invested very little in influenza vaccines."
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