The Food and Drug Administration approved four swine flu vaccines and some 45 million doses of it should be available by mid-October, federal officials said yesterday afternoon.

Preliminary trials of the vaccines showed a "robust immune response in most healthy adults eight to 10 days after a single dose," said the FDA in a statement.

The news comes on the heels of Friday's announcement that the vaccine works in just one dose rather than two, defying scientists' expectations and fears that there might not be enough vaccine to go around.

Officials spent $1 billion to secure 195 million doses of the vaccine and Health and Human Services Secretary Kathleen Sebelius says "we will have enough vaccine for everybody." Priority groups such as pregnant women and health care workers will be at the front of the line.

The FDA's stamp comes as the vaccine is still being tested in children and pregnant women, who are thought to be at greatest risk of complications from the H1N1 virus.

Results from the trials on children could be ready in a few weeks, said Dr. Wilbur Chen, a flu expert who is overseeing the clinical trials of the vaccine at the University of Maryland's Center for Vaccine Development. But trials in pregnant women will take longer, since they just began last week.

For now, Chen thinks that the results will find this vaccine is as safe and effective as the seasonal flu shot -- and for all groups of people.

Perhaps a bigger question is will everyone want one?