The Worst Flu Outbreaks In US History

Each year, influenza cases make headlines and - on occasion - people do die of the flu. Despite the fact we think of it as a mild ailment, there's a long history of flu deaths in America. Some flu seasons are more severe than others, with some of the worst flu outbreaks in history taking out thousands of citizens. 

So, which were the worst flus in the United States? Outbreaks going back all the way back to the American Revolution were deeply damaging, so many think deadly strains of the flu are a thing of the distant past. However, the worst outbreak in United States history happened only about a hundred years ago! Terrible flu seasons tend to be pretty well documented, which helps prevent flu deaths today. Scientists continually try to update medicine and basic care practices to stop the biggest influenza outbreaks from repeating themselves for future generations. While this cannot eliminate the flu altogether, doctors now know of preventative measures, vaccinations, and effective treatments that have saved countless lives over the years.

However, people can still die of the flu today!  Remember to get your flu shot every year and see a doctor if you display any symptoms of influenza. While early symptoms may not feel like one of the worst flus ever, complications can arise even in healthy adults. These past flu outbreaks should remind you that the seemingly common illness can still have deadly results. 

Photo: Indiana Public Media / flickr / CC-BY-NC 2.0

  • 1918 Spanish Flu Pandemic

    Flu Strain:  H1N1 "Spanish Flu"

    Number of Infected: >20,000,000 Americans (28% of Americans at the time)

    Number of Deaths:  >675,000 Americans

    What Made It So Deadly:  The 1918 flu pandemic is still considered possibly the worst flu outbreak worldwide in history, infecting up to one fifth of the world's population. In the United States, the flu was particularly bad. Unlike other flu strains - that targeted and killed the very young, elderly, and people with health problems - this flu took down adults who had previously been healthy, seemingly without warning. People sometimes died within hours of experiencing symptoms and, in a single year, the average life expectancy in the United States fell by 12 years. 

    Some scientist have speculated this flu was able to kill so widely because the specific variant of the virus was unusually aggressive as it mutated, and there was not yet a medicine that could effectively fight it. It was not until 1942 that the first flu vaccine was developed. It also could be passed between animals and humans, meaning there were many ways a potential victim could contract the virus. Others have said that is more likely that poor living conditions and hygiene practices, overcrowding, lack of space at hospitals, and malnourishment lead to super infections that could take out anybody, including healthy individuals. 

    The origin of the flu is still unknown, and is hotly debated.

  • 1957 Asian Flu Pandemic

    Flu Strain:  H2N2 or "Asian Flu"

    Number Infected: Unknown 

    Number of Deaths: 69,800 Americans

    What Made It So Deadly:  This flu supposedly started with a virus that was a reassortant strain, meaning that it was a cross breed between human influenza and avian (bird) influenza. Throughout the fifties, the flu underwent a series of tiny genetic mutations and modifications that eventually led to it becoming a major killer in 1957. It also came in two waves, creating a false sense of security in the population, as the first wave affected relatively few people. The second hit harder and was far more deadly.

    It was also a sneaky virus in that only some people had serious reactions to it, while many others merely had small coughs or mild fevers. These people would pass along the virus, thinking that they did not have this deadly flu. Others who caught it were sometimes more susceptible to developing complications such as pneumonia. The death toll would have been far worse, however, if scientists were not so speedy in developing and implementing a vaccine, which contained the virus before it could kill more people.

  • 2014 -2015 Flu Season

    Flu Strain:  Influenza A/H3N2

    Number of Infected:  >34,000,000

    Number of Deaths: >55,000 Including 148 Children

    What Made It So Deadly:  It is not fully known how many people died of the flu during this particularly bad flu season, though the percentage of deaths that listed the flu or pneumonia was around nine percent in the first week of January, above epidemic levels.

    It is known that the flu was very hard on children that year. The H3N2 flu had not been the most prevalent flu since around 2012, so when it reemerged, children were often the most susceptible, having no immunity to the virus. The flu had also mutated slightly, so that the vaccine we already had for that flu strain was no longer as effective. In fact, the vaccine effectiveness was estimated after the fact at a mere 19%. This meant that the number of people who fell sick, even besides children, was higher than in an average season.

  • 1968 Hong Kong Flu Pandemic

    Flu Strain:  Subtype A H3N2 "Hong Kong Flu"

    Number of Infected:  >6,000,000 Americans (By Mortality Rate)

    Number of Deaths: 33,800 Americans

    What Made It So Deadly:  Although this strain was indeed deadly, it was more widespread and infectious than it was fatal. The flu strain evolved from the widespread 1957 strain of avian flu, H2N2, and this meant that anyone who had gotten the 1957 virus had better immune protection against this specific strain. That meant that they were less likely to die from it.

    However, the Hong Kong Flu was also exceptionally contagious. It only took a few months for the virus to spread across the globe into nearly every continent. A vaccine was not developed until the flu was past its peak in many countries. It also occurred in two waves, with the second being more deadly than the first. Luckily, in the United States, the mortality rate was less than half a percent. While many developed the flu, far fewer died than in previous pandemics.

  • 1977 Russian Flu Pandemic

    Flu Strain:  Influenza A/USSR/H1N1 "Russian Flu"

    Number of Infected: Unknown

    Number of Deaths: 27,987 Americans

    What Made It So Deadly:  There still exists, to this day, a great deal of debate about whether or not this flu was accidentally released from a lab. There was a very similar strain in the late forties and early fifties that was minimized through vaccination. The strain's genetic similarity to the 1977 version led to speculation that the flu was released from a laboratory in China or Russia.

    Unfortunately, this flu was mostly an epidemic among children. Most adults still had immunity from the previous outbreak of the similar virus, but children had not been vaccinated against that particular strain and were quick to fall ill. While the flu itself seemed mild, it still killed nearly two hundred people still in their teens or younger.

    As to where this flu came from, we may never know for certain.

  • 1947 Flu Pseudopandemic

    Flu Strain: H1N1

    Number of Infected: Unknown 

    Number of Deaths: 24,000, At Peak Levels

    In 1946, there was an influenza outbreak among American troops in Japan and Korea. By 1947, the disease had spread to other military bases within the United States. The disease had mutated slightly, making it slightly different from previous influenza strains. This made it difficult to determine the cause of among sufferers.

    It also meant a previous vaccine - created in 1943 - completely failed to ward off the 1947 strain. This made the strain difficult to contain, resulting in the high number of deaths.