English: This negative stained transmission electron micrograph (TEM) shows recreated 1918 influenza virions that were collected from supernatants of 1918-infected Madin-Darby Canine Kidney (MDCK) cells cultures 18 hours after infection.

To separate these virions, the MDCK cells are spun down (centrifugation), and the 1918 virus in the fluid is immediately fixed for negative staining. The solid mass in lower center contains MDCK cell debris that did not spin down during the procedure.

Dr. Terrence Tumpey, one of the organization’s staff microbiologists and a member of the National Center for Infectious Diseases (NCID), recreated the 1918 influenza virus in order to identify the characteristics that made this organism such a deadly pathogen. Research efforts such as this, enables researchers to develop new vaccines and treatments for future pandemic influenza viruses.

The 1918 Spanish flu epidemic was caused by an influenza A (H1N1) virus, killing more than 500,000 people in the United States, and up to 50 million worldwide. The possible source was a newly emerged virus from a swine or an avian host of a mutated H1N1 virus. Many people died within the first few days after infection, and others died of complications later. Nearly half of those who died were young, healthy adults. Influenza A (H1N1) viruses still circulate today after being introduced again into the human population in the 1970s.