A scientist harvests H7N9 virus growing in bird eggs. The Centers for Disease Control and Prevention received samples of the virus from China. — James Gathany/CDC/Douglas E. Jordan / (CC0 1.0)
Scientists in Switzerland have cracked open a centuryold viral mystery by decoding the genome of the 1918 influenza virus from a preserved Zurich patient.
The ancient RNA has revealed that the virus had already adapted to humans at the very start of the pandemic, carrying mutations that made it both more infectious and more immuneresistant.
This insight, from University of Zurich, was made possible by pioneering a new method to recover fragile RNA from preserved tissue, researchers gained rare insights into how flu viruses evolve. In terms of its significance, the study not only revives the history of one of humanity’s deadliest outbreaks but it also arms scientists with critical knowledge to face future pandemics with smarter, sciencebased strategies.
The Influenza Pandemic of 1918
The 1918–1920 flu pandemic, also known as the Great Influenza epidemic, was an exceptionally deadly global influenza pandemic caused by the H1N1 subtype of the influenza A virus.
Nearly a third of the global population, or an estimated 500 million people became infected. Estimates of deaths range from 17 million to 50 million, and possibly as high as 100 million, making it the deadliest pandemic in history.
The virus is an enveloped negativesense RNA virus, with a segmented genome. Through a combination of mutation and genetic reassortment the virus can evolve to acquire new characteristics, enabling it to evade host immunity and occasionally to jump from one species of host to another.
New study
By comparing the Swiss genome with the few influenza virus genomes previously published from Germany and North America, the researchers were able to show that the Swiss strain already carried three key adaptations to humans that would persist in the virus population until the end of the pandemic.
Two of these mutations made the virus more resistant to an antiviral component in the human immune system – an important barrier against the transmissions of avianlike flu viruses from animals to humans. The third mutation concerned a protein in the virus’s membrane that improved its ability to bind to receptors in human cells, making the virus more resilient and more infectious.
According to lead researcher Verena Schünemann: “This is the first time we’ve had access to an influenza genome from the 19181920 pandemic in Switzerland. It opens up new insights into the dynamics of how the virus adapted in Europe at the start of the pandemic.”
Viruses today
New viral epidemics pose a major challenge to public health and society. Understanding how viruses evolve and learning from past pandemics are crucial for developing targeted countermeasures.
Going forwards, the new method can be used to reconstruct further genomes of ancient RNA viruses and enables researchers to verify the authenticity of the recovered RNA fragments.
Schünemann says: “A better understanding of the dynamics of how viruses adapt to humans during a pandemic over a long period of time enables us to develop models for future pandemics…Thanks to our interdisciplinary approach that combines historicoepidemiological and genetic transmission patterns, we can establish an evidencebased foundation for calculations.”
The research appears in the journal BMC Biology, titled “An ancient influenza genome from Switzerland allows deeper insights into host adaptation during the 1918 flu pandemic in Europe.”
