SWIFTWATER, Pa. (AP) — The federal government originally promised 120 million doses of swine flu vaccine by now. Only 13 million have come through. As nervous Americans clamor for the vaccine, production is running several weeks behind schedule. Health officials are blaming the pressure on pharmaceutical companies to crank it out along with the ordinary flu vaccine. They also cite a slow and antiquated process that relies on millions of chicken eggs. There have been other bottlenecks, too: Factories that put the precious liquid into syringes have become backed up. And the government itself ran into a delay in developing the tests required to assess each batch before it is cleared for use. What effect the delays will have on the course of the outbreak is unclear. That's in part because scientists cannot say with any certainty just how dangerous the virus is, how easily it spreads, or whether it will mutate into a more lethal form. Since April, swine flu has killed more than 800 people in the U.S., including 86 children, 39 of them in the past month and a half, according to the Centers for Disease Control and Prevention.