Scientists have confirmed for the first time that the new H1N1 virus did come from pigs.
The Centers for Disease Control did a genetic breakdown of 70 swine flu samples from the United States and Mexico and found the virus has probably been circulating in pigs for years, but they still aren't sure how it infected humans.
More than 6,500 cases are now confirmed or likely in the U.S.
Still, the CDC says that's just the "tip of the iceberg".
They're expecting 100,000 cases before it's all over.
"What we're hearing is some parts of the country are experiencing decline in the number of cases and activity and in other areas they're still having focal outbreaks and increases," said the CDC's Dr. Richard Besser.
The government has produced new public service announcements and brought in Sesame Street's "Elmo" to remind children that hand washing is one of the best ways to fight swine flu.
The Secretary of Health and Human Services announced the government will spent a billion dollars this summer on clinical trials and to produce the beginnings of enough swine flu vaccine to protect health care workers in the fall.
"We need to be ready and have everything in place so we can move quickly should an immunization program be deemed necessary," said Health and Human Services Secretary Kathleen Sebelius.
The decision to authorize full production may not happen for a couple of months.