WHO maintains 2 billion estimate for likely H1N1 cases

The World Health Organization stuck on Tuesday to its statement that about two billion people could catch H1N1 influenza by the time the flu pandemic ends. But the estimate comes with a big health warning: no one knows how many people so far have caught the new strain, known as swine flu, and the final number will never be known as many cases are so mild they may go unnoticed. "By the end of a pandemic, anywhere between 15-45 percent of a population will have been infected by the new pandemic virus," WHO spokeswoman Aphaluck Bhatiasevi said in a statement. "Thirty percent is a midpoint estimate and 30 percent of the world's population is 2 billion."