The World Health Organization says all of humanity is now under threat from a swine flu pandemic, but nobody knows how severe it might turn out to be. Compared to the flu epidemics that occur every year, not that many people have died, and the WHO's warning is designed to keep things from getting worse. Mexico City, near where the outbreak began, is virtually shut down. But experts are warning about the dangers of over-reaction. Today President Obama called a cabinet meeting to talk the H1N1 virus, which officials are calling by its scientific name because it's now transmitted from human to human and not just from pigs. He cautioned against “alarm,” but acknowledged the need to prepare for the long term “since we know that these kinds of threats can emerge at any moment.“ The virus cannot be stopped by shutting down borders, so what can be done? Are public health systems prepared? If it gets worse, can a vaccine be ready in time?