Virus samples taken from 100-year-old lungs reveal that the influenza virus responsible for the 1918 flu pandemic mutated into multiple variants, similar to how Covid-19 has done in the current pandemic.

Even though the findings are not directly applicable to the current Covid-19 pandemic, they prove that variants should be expected – and that we can overcome them.

Lead author of the study and evolutionary biologist at the Robert Koch Institute in Berlin, Germany, Sébastien Calvignac-Spencer, said, “Those [viral infections] in the second wave look like they were better adapted to humans. Just like today, we wonder whether the new variations behaved differently or not than the original.”

So, to try to find some answers, Calvignac-Spencer and his colleagues obtained six human lungs from people who lived during the 1918 pandemic. They had been preserved in formalin in pathology archives in Germany and Austria.

According to the researchers, three of the lungs – two from soldiers who died in Berlin and one from a young woman who died in Munich – had the 1918 influenza virus present in them.

The same virus that was responsible for the pandemic 100 years ago actually still circulates today. However, it was far deadlier back then because humans today descended from those who survived the infection. So they’ve inherited some form of immunity.

Estimates suggest that this virus infected almost 1 billion people around the world. At the time, the global population was only 2 billion. Between 50 million and 100 million people died across three waves of the disease.

The forms of the virus found in the two German soldiers showed almost no genetic differences between the two. However, the virus in the lungs of the young woman showed several differences. The soldiers died in the first wave of the pandemic, while the young woman died in a later wave.

The researchers conducted lab studies with replicas of parts of the virus to determine how successfully different variants infected and replicated inside human cells.

Their findings indicate that the virus mutated to become more effective by evolving to better dodge cellular defense against infection. The researchers believe the mutations between the first and second waves made the virus better at spreading among humans, rather than between birds, which is where it originated.

Another mutation changed how the virus interacts with MxA, a human protein that helps the body build an immune response to new pathogens.

“It’s predicted that these changes helped the virus to evade one of the mechanisms that [human] cells use to shut down influenza viruses,” Calvignac-Spencer said.

We are seeing the same evolutionary processes in today’s Covid-19 pandemic. However, since science has progressed so much, we can learn more about today’s pandemic than scientists ever could during the 1918 pandemic. “The more we can learn about the current pandemic, the more that can help us understand the past pandemic, rather than vice versa,” Calvignac-Spencer said.