In order for a disease to become a pandemic, three things must happen: There must be a virus or other organism that infects humans and causes severe disease, the population has to be susceptible to the organism and there must be person-to-person transmission.
"The flu can easily become a pandemic, but the recent outbreaks of H1N1 and bird flu didn't reach this level," said Dr. James P. Steinberg, professor of medicine at Emory University School of Medicine in Atlanta. "Bird flu wasn't spread that easily from person to person and H1N1 wasn't that severe a virus."
Although the nightmarish scenario of a virus gone wild is realistic, experts say it's important not to panic.
"Yes, we have been locked in this battle with microbes since we became modern humans, but we are not defenseless and we are also continuously looking at new tools to keep microbes in check," Khan said.
The CDC investigates possible outbreaks every week, Reynolds added.
"We know that sooner or later the scenario in 'Contagion' will happen, but we are not helpless to deal with it," said Ira Longini, a professor of biostatistics at the University of Florida in Gainesville.
Another important lesson from the film is the need for the country to be ready whenever the next outbreak happens.
"Under the radar, there have been a very significant reduction in disaster preparedness and response funding," said Dr. Irwin Redlener, director of the National Center for Disaster Preparedness at Columbia University's Mailman School of Public Health. "I would be more than happy to have this film stimulating a discussion about why we are undermining our preparedness."