"I don't want anybody to be alarmed, but I do want everyone to be prepared," he said.
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 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.
Like the seasonal flu, swine flu spreads through coughs and sneezes of people who are sick. Obama said there are common sense precautions people can take to lower their risk of infection, like washing their hands frequently and staying home if they feel sick.
"I know it sounds simple, but it's important and it works," Obama said.