U.S. health officials say there have been no problems so far in tests of the new swine flu vaccine.

Participants earlier this month got their first shots of the vaccine. Health officials on Friday said there have been no serious side effects reported.

While the vaccine so far appears to be safe, doctors won't know until next month whether it's effective against swine flu.

Government officials think around 50 million doses of vaccine could be available to the public by mid-October. Nearly 8,000 hospitalizations and 522 deaths have been reported in the United States since swine flu virus was first seen in April.