Researchers in Switzerland have successfully reconstructed the genome of the virus responsible for the deadly 1918–1920 Spanish flu pandemic. This breakthrough could help shape strategies for future pandemics.
A team of scientists from the University of Basel and the University of Zurich has decoded the genome of the influenza virus that caused one of the deadliest pandemics in modern history. Using a preserved tissue sample over 100 years old, the researchers uncovered how the virus had already adapted to humans at the very beginning of the outbreak.
Genetic Code Reconstructed from a Century-Old Sample
The analyzed specimen belonged to an 18-year-old patient who died in Zurich during the first wave of the pandemic in July 1918. Stored in UZH’s Medical Collection, the formalin-fixed sample allowed researchers to extract and study the viral RNA—a rare achievement given the fragility of RNA over time.
This marks the first-ever Swiss genome sequence of the 1918 influenza virus, opening new doors to understanding how the virus spread and evolved in Europe.
Three Key Human Adaptations Identified
According to Professor Verena Schünemann, who led the study, the Swiss virus genome revealed three critical mutations that helped the virus better infect human hosts:
- Two mutations made the virus more resistant to antiviral components of the human immune system.
- The third mutation enhanced the virus’s ability to bind to human cell receptors, increasing its infectiousness and resilience.
These mutations were present early on and persisted throughout the pandemic.
New Method Developed to Recover Ancient RNA
Unlike DNA viruses, RNA viruses like influenza degrade much faster over time. That’s why the team developed a new RNA recovery method, making it possible to retrieve and verify ancient viral genomes. Christian Urban, the study’s lead author, emphasized that this innovation could help reconstruct other ancient RNA viruses in the future.
Medical Collections: A Hidden Scientific Treasure
The research was made possible through collaboration with UZH’s Medical Collection and the Berlin Museum of Medical History. Professor Frank Rühli highlighted that such collections are undervalued archives that can significantly contribute to virus evolution studies and pandemic preparedness.
Preparing for Future Pandemics
The researchers believe that insights from past pandemics are essential for anticipating the course of future outbreaks. “Understanding how viruses adapt to humans over time gives us a solid foundation for modeling future pandemics,” said Schünemann.
Dr. Kaspar Staub added that combining historical epidemiology with genetic data enables the creation of evidence-based predictive models. However, further genome reconstructions and long-term studies are needed to refine these models.
Cover Image Credit: Emergency hospital in Zurich’s Tonhalle during the so-called “Spanish flu” in November 1918 (Image: Schweizerisches Nationalmuseum, Inventarnummer LM-102737.46)
Christian Urban et at. An ancient influenza genome from Switzerland allows deeper insights into host adaptation during the 1918 flu pandemic in Europe. BMC Biology. 1 July 2025. DOI: https://doi.org/10.1186/s12915-025-02282-z
