WHO: Swine Flu Could Infect 2 Billion Worldwide

Of course, these numbers are pure speculation and are based on past pandemics that have moved around the world. Officials are quick to point out that the world has changed considerably since the last pandemic and that it's impossible to predict whether the swine flu would follow similar patterns.

It's also important to note that the severity of the infections of swine flu are also difficult to predict. Experts explained that, even if 2 billion people were actually infected with the virus, only about half of those would show any symptoms. And for those that did have symptoms, about half of those would be so mild as to not even realize that they were actually sick. But, even with a generally mild illness such as the swine flu, the virus will weaken those who are already in poor health and the sheer number of people infected would inevitably mean some mortality rate would be realized.

The likely time line for a pandemic to unfold would be several weeks or months and it would be difficult for health officials to ever have an accurate count of those infected, for the reasons cited above. It seems likely that, if a pandemic occurs, it will be driven by young people as they congregate in schools and other events. Once together in such large groups, the virus can easily and rapidly spread. The incubation period for the virus seems to be up to one week, which means that many people are infected and spreading the virus before they ever realize that they are sick.