It shows how deadly viruses can weaken over time to mild variants that circulate annually.

In the year 1918, the second deadliest pandemic ever emerged. We are talking about the Spanish flu, which can directly rally behind the Black Death. The Spanish flu pandemic, caused by the H1N1 virus, hit Europe in four waves and claimed tens of millions of lives. In a new study researchers have mapped this ancient virus. And surprisingly, this shows that the well-known seasonal flu may be a descendant of the deadly Spanish flu.

Spanish flu

Between 17 and 100 million people died during the Spanish flu pandemic that lasted from 1918 to 1920. Because the virus made an appearance in the final months of the First World War, the relocation of military personnel is believed to have accelerated its spread. Although the pandemic was widespread, its causes were not well understood at the time. The flu has been variously attributed to the spread of bacteria, mosquitoes, and even cannon fire. It was not until 1933 that the flu virus was isolated for the first time.

Why is the Spanish flu called the Spanish flu?
Countries fighting in the war generally censored news about the spread of the virus to maintain public morale. Spain’s neutrality in the conflict meant that Spain was one of the few countries to openly report on the spread of the deadly flu. This created the impression that the virus originated in Spain – leading to the pandemic being dubbed the Spanish flu. Still, to this day no one knows where the outbreak started. Despite the first confirmed cases coming from the US, the virus probably spread undetected for months or years before that.

Because it took so long to discover the virus, samples containing the virus are rare. This makes it difficult to determine exactly what the virus looked like. “When we started our study, there were only 18 copies of which genetic sequences were available and only two complete genomes,” said study researcher Sébastien Calvignac-Spencer. “Most of these came from the US and only two from London.”

Study

In the new study, the researchers combed through museums for tissues from ill-fated victims of the Spanish flu. The search leads to the discovery of three new samples, found in the collection of the Berlin Museum of Medical History. And these samples provide surprising new insight into the flu virus during the first wave in 1918. “Our analysis of the Berlin samples allowed a complete genome sequence of the virus,” said researcher Thorsten Wolff.

Findings

It leads to some interesting findings. As expected, the new analysis clearly suggests that the 1918 flu virus spread both locally and across continents. In addition, it appears that the different waves were not caused by different variants of the virus – as we saw during the corona pandemic – but always by the same strain.

seasonal flu

What’s most interesting, though, is that the current seasonal flu appears to have descended directly from the pandemic virus of a hundred years ago. Eight segments of RNA that make up the genome of the seasonal flu virus can be directly associated with the H1N1 virus. In short, the seasonal flu virus may be the descendant of one of the deadliest viruses in human history.

It means that the deadly virus that claimed many victims in the early 20th century became less and less virulent, changing from a pandemic virus to a seasonal virus. This also shows how deadly viruses can weaken over time to mild variants that circulate annually. Whether that also applies to the coronavirus and whether a meek and mild future can also be the fate of SARS-CoV-2, remains to be seen.