One hundred years ago, the major powers of Europe were still locked what was then known as the “Great War,” while the U.S. was gearing up to enter the conflict. Ultimately, the First World War would result in the deaths of 20 million people. However, a virus was spreading – and would prove to be far deadlier than the new mechanized war machines defining that conflict.

Over the next fifteen months, that virus, identified as a subtype of avian strain H1N1 and eventually dubbed “Spanish Flu,” went on to kill as many as 100 million people across the world – 5% of the global population at that time. In the U.S. alone, it killed more people in one year than the AIDS epidemic killed over four decades. In some cases, it killed a person within hours – and over half of those who died were otherwise healthy people between the ages of 20 and 45.

This year, a particularly virulent strain of the flu has killed at least 24 children. Currently, the Centers for Disease Control (CDC) considers it the worst flu season in recent history. This raises the question: could we experience a replay of 1918?

Concerns about another deadly pandemic on the scale of a century ago are being fueled by a number of factors. First, this season’s strain, H3N2, is the most lethal, having been responsible for particularly bad outbreaks in 1997-98 and 2003-04. Secondly, there have been more cases reported, as well as a recent spike in hospitalizations. Thirdly, several clinics and pharmacies are running low on the vaccine. Finally, there has been a reduction in the number of people who have been inoculated. This week, the CDC reported that 6.6% of patients currently seeking medical attention have flu symptoms – an increase of .06 percent over the 2014-15 season.

Anne Schuchat, deputy director of the CDC, expressed her own fears recently at a seminar on the pandemic of the last century. “You think about how bad it was in 1918, and you would think surely our modern medical technology will save us,” she says. “But influenza is the Hollywood movie writer’s worst nightmare. We have many more tools than we had before, but they are imperfect.”

John M. Barry, a historian who authored a best-selling book on the 1918 pandemic, agrees. “We still have no control over the virus,” he says. “In a lot of ways, we’re more vulnerable to another pandemic because there is more interdependence.”

One of the problems is the nature of the influenza virus. Most vaccinations – such as those against smallpox and polio – consist of a small amount of the pathogen. It isn’t enough to infect someone, but it will activate the subject’s immune system so that the next time the pathogen is encountered, the body’s defenses will recognize it. Unfortunately, the influenza virus is a bit of a chameleon, able to disguise itself from white blood cells.

The good news is that while a flu vaccine may not always prevent a person from contracting the disease, the vaccine can still mitigate the worst of the symptoms. Dr. Susan Donelan, a professor at the Stony Brook University School of Medicine, specializes in infectious diseases. She notes that although someone who has been vaccinated can still contract the flu, it “can still keep people from getting really ill, and if hospitalized, can keep them from dying.” Lance Wheeler, who runs a healthcare operation in North Carolina, appeared on a Raleigh television news program recently and pointed out that “…about 90 percent of the deaths associated with the flu have been people not vaccinated.”

Although vaccines are still in short supply in some areas, they are still available. People who still need a flu shot can usually find sources through their state health agency websites.