Surprising link between the 1918 pandemic and modern flu

The 1918-1919 flu pandemic killed between 17 and 100 million people worldwide. But, while some virus genomes have been sequenced and it is now known to be an H1N1 flu, there is still a lot of mystery surrounding it. Viral and genetic material usually survives very poorly, leaving many unknowns.

Now, an analysis of newly discovered samples suggests that one of our seasonal flu strains may be a direct descendant of the virus that caused the 1918 pandemic.

An international team of researchers discovered the flu in 1918 and 1919 lung samples, kept in the archives of the Berlin museum. Sébastien Calvignac-Spencer, researcher at the Robert Koch Institute in Germany and co-author of an article describing the research, published in Nature Communication, says the team was investigating lung samples stored in the basement of a local museum, to see if they could extract information about respiratory viruses the owners had had.

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“Honestly, I didn’t have much hope. I was wrong, because it worked like a charm from day one. We were quickly able to assemble the full genome and collect genome-wide information for two more specimens,” explains Calvignac-Spencer.

“The 1918 Spanish flu is still a big mystery,” says co-author Thorsten Wolff, also from the Robert Koch Institute.

“So when Sebastien contacted me saying, ‘Oh, we just found relics of the virus, more or less in our garden,’ I was completely excited and interested in looking at those genomes.”

The researchers found that the genomes differed significantly from other previously reconstructed 1918 flu genomes. There were also some key changes between older and younger versions of the virus, which likely allowed the flu to better evade the virus. human immune system.

Because the specimens come from before the peak of the pandemic — and then during its peak — they provided information about how the virus evolved. This evidence implies that the modern H1N1 seasonal flu is a descendant of the 1918 flu, having become much less virulent as it evolved.

The samples also show that – much like COVID-19 – the 1918 flu evolved into new strains and spread across the world.

“There was also genomic variation during this pandemic,” says Calvignac-Spencer.

“And when we interpret this variation, we detect a clear signal for frequent transcontinental dispersal. It’s not very surprising in these times, but it’s good to show.

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Not all pandemics are equal. In historical samples, “we also show that there is no evidence of lineage replacement between waves, as we see today with two different variants of SARS-CoV-2 that have replaced each other.

Nevertheless, it offers data on the global possibilities of a pandemic. “Another thing we discovered with the sequences and the new statistical models is that the seasonal virus that continued to circulate after the pandemic may well have directly evolved from the pandemic virus entirely,” he says.

This contradicts the most popular current hypotheses about the origins of H1N1. Calvignac-Spencer cautions that all of their results are tentative, based on small samples as they are.

“A major limitation of this type of research that we only have a very limited sample. So you have to stay humble. »

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