The strand of the Spanish flu never disappeared and is still with us
But the strand of the flu didn’t just disappear. The influenza virus continuously mutated, passing through humans, pigs and other mammals. The pandemic-level virus morphed into just another seasonal flu. Descendants of the 1918 H1N1 virus make up the influenza viruses we’re fighting today.
“The 1918 flu is still with us, in that sense,” explained Ann Reid, the executive director of the National Center for Science Education in the US who successfully sequenced the genetic makeup of the 1918 influenza virus in the 1990s. “It never went away.”
“As many as 8 to 10 percent of all young adults then living may have been killed by the virus,” historian John M. Barry wrote in his best-selling book “The Great Influenza.”
All the while, World War I continued. The bloody trench warfare across Europe left 8.5 million or more soldiers dead. The tight quarters during the war only aided the spread of the virus, said Howard Markel, a physician and medical historian at the University of Michigan.

The 1918 outbreak has been called the Spanish flu because Spain, which remained neutral during World War I, was the first country to publicly report cases of the disease. China, France and the United States already had cases of the flu, but wartime censorship largely kept the outbreaks out of the newspapers.
Then, the king of Spain — Alfonso XIII — and several other members of his government contracted the flu. This series of unfortunate events left a permanent mark, tying the country to the deadly outbreak.