English: This 2005 photograph depicts one of the Centers for Disease Control and Prevention’s staff microbiologists examining reconstructed 1918 Pandemic Influenza Virus contained within a calibrated vial with a supernatant culture medium.

The photo is taken in a Biosafety Level 3-enhanced laboratory setting, where scientists work beneath a flow hood, where air outside the hood is pulled into the hood's confines and is then filtered of any pathogens before being recirculated inside the self-contained laboratory atmosphere.

The 1918 virus was recreated 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.