Researchers have worked for years to try to understand the origin of the Spanish flu, a pandemic responsible for 25 to 50 million deaths at the end of World War I, in 1918. In a study published by the Accounts of the United Nations ‘American Academy of Sciences (Pnas) Monday, April 28, the team of biology professor Michael Worobey at the University of Arizona, in the United States, explains having solved the mystery.
According to the results of the study, the 1918 virus was born from a mixture of a human (H1) strain of seasonal influenza and avian genes of the N1 type. This encounter gave birth to the H1N1 virus, ancestor of the variant that made its big comeback in 2009, but nearly 10,000 times more virulent. The 50,000 to 70,000 young American soldiers gathered in Kansas would have been the first to be infected, before crossing the country to reach Europe. Indeed, the Spanish flu takes its name from Spain because it was the only country, not concerned by military secrecy, to have spoken about it.
Unimmunized young adults
While previous influenza had primarily affected babies and the elderly, the Spanish flu wiped out young adults aged 25 to 29 around the world. The patients died of a bacterial superinfection which manifested itself 4-5 days after the appearance of the first flu-like symptoms. The absence of antibiotics, the hygienic conditions of the time and the large gatherings of the post-war period increased the risks of epidemics and the difficulties in treating the disease.
If young adults have been particularly affected, it is because their generation had been immunized against the virus type H3N8, but not against the H1, explains Professor Worobey.
