The World Health Organization said Thursday that up to 2 billion people could be infected by swine flu if the current outbreak turns into a pandemic. The agency said a pandemic typically lasts two years.

WHO flu chief Keiji Fukuda said the number wasn’t a prediction, but that experience with flu pandemics showed one-third of the world’s population gets infected.

“If we do move into a pandemic then our expectation is that we will see a large number of people infected worldwide,” Fukuda said. “If you look at past pandemics, it would be a reasonable estimate to say perhaps a third of the world’s population would get infected with this virus.”

The H1N1 Swine Flu is though to be on the decline right now in North America, where it is currently most prevalent – but based on past Swine Flu or H1N1 Flu infections, there will be multiple waves of the Flu, with varying levels of danger. Curreently the H1N1 Swine flu is invading South America, where it is prime flu season, sparking fears that the Swine Flu H1N1 Virus may mutate further and come back to North America later this year in a more virulent, contagious and dangerous form.