Spanish flu was the most devastating pandemic ever recorded, leaving major figures like medical philanthropist Bill Gates to draw comparisons to the ongoing COVID-19 pandemic. How did the 1918 Spanish flu pandemic cause such a high death toll? And how has the Spanish flu prepared us for coronavirus?

It started as a mild flu season, not different from any other. When its first wave hit in the spring of 1918, the Spanish flu seemed like just another flu. But then the second wave began at the end of summer.

In November of the same year, a tiny Alaskan village, mostly comprised of Inuit Natives, was one of the first to see the virus’ deadliest manifestation. In the span of five days, in a village with about 80 adult residents, 72 adults lost their lives to the infection, according to the CDC.

Spanish flu would become the world’s worst pandemic on record, killing an estimated 50-100 million people worldwide, according to Jeffrey Taubenberger, MD, PhD, writing for the CDC’s Emerging Infectious Diseases journal. This included 675,000 people in the United States. What can the world’s worst flu outbreak tell us about the coronavirus COVID-19 pandemic?

Similarities Between Spanish Flu and Coronavirus

For one, both diseases seemed to originally come from an animal source. Research into H1N1 Spanish flu virus genes suggests the deadliest wave of the outbreak came from a bird, though no one knows for certain what type or where it came from exactly.

Likewise, health experts suspect an animal originally hosted the COVID-19 coronavirus strain before it started to infect humans, though the animal has still not been identified.

This leads to another comparison. The Spanish flu became much more dangerous after an apparent mutation. Likewise, strains of coronavirus are known to mutate relatively easily.

In fact, this has happened twice before, according to an article edited by MedicineNet editor Charles Patrick Davis, MD, PhD:

“Prior mutations led to the 2002-2003 SARS outbreak, in which a virus native to civet cats mutated to spread the illness to humans. In Saudi Arabia in 2012, a coronavirus that infected camels mutated to become infectious in humans, leading to the MERS outbreak.”

Infection Rate

Another similarity is how quickly both viruses seem to spread. Spanish flu infected an estimated 1/3 of the global population. And although much remains unknown about COVID-19, the disease has spread rapidly from its origin in China in late December of 2019 and now can be found on every continent except Antarctica. As of January 2022, the World Health Organization recorded more than 315 million confirmed cases of COVID-19.

Mortality Rate May Be Similar for Coronavirus (COVID-19)

The death rate of Spanish influenza was vastly greater than the average seasonal flu, Dr. Taubenberger said. The case-fatality rate is estimated to have been greater than 2.5%. This means for every 100 recognized cases, on average more than two and a half people died. By comparison, he says, the fatality rate in subsequent flu pandemics has been less than .1%.

Comparisons are hard to determine. Since new information about COVID-19 is calculated by different organizations and governments in different ways, much work remains to determine the disease’s true case-fatality rate.

How Spanish Flu and Coronavirus Differ

But Spanish flu is different from COVID-19 coronavirus in important ways. According to National Geographic, Spanish flu killed with deadly speed, with many reports of people who woke up sick, then died on their way to work. It was also indiscriminate in killing both young and old alike. In contrast, COVID-19 infections take several days if not weeks to cause death, and elderly populations are much more vulnerable to COVID-19 than children and young adults.

But perhaps the most important difference between the two viral diseases comes down to historical timing. The Spanish flu pandemic coincided with World War I, which helped the disease quickly spread along with mobilized troops from place to place. In contrast, many nations have enacted travel restrictions to areas high in coronavirus COVID-19 infections with the purpose of preventing quick spread.

What Remains Unknown About Coronavirus

Coronavirus COVID-19 has never been seen before this outbreak. As a result, there are many details about the infection that remain unknown. Multiple variants have changed the picture of the ongoing pandemic several times, including the Delta variant and the Omicron variant.

One of the most pressing questions is whether coronavirus will go away anytime soon. The impact of the Spanish flu was vast and continues to this day. Descendants of the virus can still be found in pigs, Dr. Taubenberger said. And ever since a lab accident in 1977, nearly all human cases of influenza A have been caused by Spanish flu viral descendants. COVID-19 is likely to continue circulating for a long time, according to many health experts.