With a potentially deadly swine flu outbreak looming, President Obama is urging Americans to take steps to prevent infection. He says that while the government is preparing across all levels, Americans have a role to play in the response as well. "I don't want anybody to be alarmed," he states. "But I do want everyone to be prepared." The global swine flu epidemic first emerged in April, sickening more than 1 million Americans and killing about 500. More than 2,000 people have died worldwide. Health officials are preparing for a surge in cases this fall, and one White House report from a panel of experts suggests that up to half the U.S. population could catch swine flu during a pandemic. Vaccine development is ongoing and is likely to be available by October. The president said the vaccine for swine flu - known as the H1N1 virus - would be voluntary, but "strongly recommended." Certain groups are more vulnerable to swine flu, including children under 2, pregnant women and people with health problems like asthma, diabetes and heart disease.