Both caused global pandemics; here's how they compare in terms of symptoms, treatment, and death toll.

Since the early days of the COVID-19 pandemic, comparisons have been drawn with previous pandemics, most often the H1N1 influenza pandemic of 1918 (known as Spanish flu).

Like COVID-19, the 1918 virus was "novel," meaning it was a new virus that hadn't been seen before. Also like COVID-19, nobody had immunity to it and it was highly infectious, spreading through respiratory droplets. Here's the lowdown on Spanish flu, including how it compares to COVID-19, if it was eradicated, and how long people wore masks to protect themselves from it.

Where did Spanish flu come from?

Despite its name, the first recorded cases and deaths from Spanish flu were in the US, France, Germany, and the UK. Most countries—already suffering from the devastating effects of World War I—imposed censorship on their press. But Spain remained neutral during the war, which meant national newspapers reported freely on the impact of the virus. This led to the false impression that the virus originated in Spain.

"There is much debate about where the 1918 influenza pandemic truly originated from," epidemiologist Supriya Narasimhan, MD, division chief of infectious diseases and medical director of infection prevention at Santa Clara Valley Medical Center in San Jose, California, tells Health. "I prefer to not call it 'Spanish' flu and link it geographically with Spain, because that can be perceived as stigmatizing––much like why we no longer call COVID-19 the 'Wuhan' virus."

How was Spanish flu transmitted?

The 1918 virus (Influenza A Subtype H1N1) and the new coronavirus (SARS-CoV-2) are different viruses from different viral families, infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, tells Health.

However, the mode of transmission is very similar. They are both spread primarily through respiratory droplets and aerosols (a suspension of liquid droplets in air), Charles Bailey, MD, medical director for infection prevention at Mission Hospital and St. Joseph Hospital in Orange County, California, tells Health. "This makes close, face-to-face contact crucial to their spread through a community," he says.

How long did Spanish flu last?

The 1918 influenza pandemic lasted for two years, occurring in three waves, per the Centers for Disease Control and Prevention (CDC). The first wave began in March 1918, and the second wave—when the pandemic peaked in the US—came in the fall. The devastating second wave passed by December 2018, but there was more to come. In January 1919, a third wave started in Australia and worked its way to the US and Europe. By the summer of 1919, the third wave subsided.

So, what happened to the Spanish flu? Although the virus never completely disappeared, people had developed a collective immunity to it by 1920.

How long did people wear masks during Spanish flu?

In 1918, health authorities urged people to wear masks to slow the spread of disease. Back then, they were made of gauze and cheesecloth, and those who refused to wear them faced a fine or even imprisonment in cities that mandated them, reported The New York Times. Still, many people resisted—as is happening right now during the COVID-19 pandemic.

What were the symptoms of Spanish flu?

Both Spanish flu and COVID-19 manifest as "influenza-like illnesses," with fever, muscle aches, headache, and respiratory symptoms most common, Dr. Bailey says. "One symptom that seems unique to COVID-19, and not seen in seasonal influenza—or, to my knowledge, Spanish flu—is loss of taste and/or smell," he adds.

The similarity in symptoms is one reason doctors and scientists are pushing hard to get everyone vaccinated against the flu, Bruce Polsky, MD, chairman of medicine at NYU Langone Hospital—Long Island, tells Health. "If someone has symptoms but we can't entirely rule out the flu, we can move it to a lower probability on the diagnosis list," he explains.

Who was most affected by Spanish flu?

Mortality was high in people younger than 5 years old and 65 years and older. But younger adults (ages 20 to 40) were the most at risk, Dr. Adalja says.

"Mortality was also high among pregnant women, those in lower socioeconomic classes, and immigrant populations," Dr. Narasimhan adds. The deaths in very different demographic groups is one of the key differences between Spanish flu and COVID-19.

What's more deadly: COVID-19 or Spanish flu?

On September 29, the global COVID-19 death toll topped 1 million people, and as of November 17, the figure is 1,332,470 deaths, according to the Johns Hopkins Coronavirus Resource Center.

We don't have an accurate death count for Spanish flu, but estimates range from 17 to 50 million people across the world, and there were possibly even more. The CDC says an estimated one-third of the world's population was infected with the virus, resulting in at least 50 million deaths.

Why did the Spanish flu kill so many people—didn't treatment exist?

Why did so many people die of Spanish flu? First of all, the state of supportive medical care in 1918-19 was primitive by today's standards. "Keep in mind that many deaths related to influenza are actually due to secondary bacterial infections, which today we treat with antibiotics, which were completely unavailable in 1918-19," Dr. Polsky explains. "Additionally, the state of ICU care with modern mechanical ventilation and ECMO (extracorporeal membrane oxygenation. when blood is pumped through an artificial lung back into the bloodstream) were far off into the future."

Dr. Narasimhan points out that no vaccine or antiviral agent was available. "We did not have the scientific advancement for vaccine development, which would have prevented transmission and decreased disease severity and mortality."

The backdrop of World War I was also hugely instrumental in the transmission of the virus that caused Spanish flu. "Military barracks usually have crowding and poor spatial separation, especially in winter months," Dr. Narasimhan says. "The movement of the troops during the war facilitated spread to other susceptible populations. Likewise, the economic circumstances likely caused crowding in winter months, poor ventilation, and congregation—all of which increased spread."

Also, standards of hygiene were lower 100 years ago. "But interestingly, the advice given during that time is nearly identical to what we advise for COVID-19: masking, keeping away from sick people, and washing your hands," Dr. Narasimhan notes.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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