A surprising link between the 1918 pandemic and modern influenza

The Influenza pandemic 1918-19 It killed between 17 million and 100 million people worldwide. But, while some of the virus’s genomes have been sequenced and is now known to be the H1N1 flu, there is still a lot of mystery about it. Viral and genetic material usually survives very poorly, leaving many unknowns.

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

An international team of researchers discovered lung samples of influenza in 1918 and 1919, kept in the archives of museums in Berlin. Sebastian Kalviniak Spencer, a researcher at the Robert Koch Institute in Germany and co-author of a paper describing the research, published at nature connections, He says the team was investigating lung samples in the basement of a local museum, to see if they could extract any information about which respiratory viruses the owners were.

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“Quite frankly, I wasn’t too optimistic. I was wrong, because it worked out beautifully from day one. We were quickly able to piece together the complete genome and gather extensive genome information for two other samples,” says Calvinac-Spencer.

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

“So when Sebastian called me up and said, ‘Oh, we just found some remains of the virus, more or less in our own backyard,’ I was totally excited and was interested to take a look at this genome.”

The researchers found that the genomes differ significantly from other genomes reconstructed prior to the 1918 flu. There were also two major changes between older and younger versions of the virus, both of which likely made the flu better at evading the human immune system.

Because the samples came before the epidemic’s peak – and then during its peak – they provided information about how the virus developed. This evidence indicates that the modern seasonal H1N1 influenza is a descendant of the 1918 influenza, becoming less virulent as it developed.

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

“There was genomic variation during that epidemic as well,” Calviniak Spencer says.

“And when we explain this difference, we find a clear indication of frequent dispersal across continents. It is not very surprising in these times, but it is good to show.

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Not all epidemics are created equal. In the historical samples, “we also showed that there is no evidence of lineage substitution between waves, as we see today with two different SARS-CoV-2 variants replacing one another.

However, it does provide data on the global probability of a pandemic. “Another thing we’ve discovered with new statistical sequencing and models is that the later seasonal virus that continued to circulate after the pandemic may have been a direct evolution from an entirely pandemic virus,” he says.

This contradicts the most common current hypotheses about the origins of H1N1. Calvinac Spencer cautions that all of their findings are provisional, based on small samples as they are.

“One major limitation of this type of research is that we only have very limited samples. So we have to remain modest.”