SWIFTWATER, Pa. — The federal government originally promised 120 million doses of H1N1, or 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, and health officials blame the pressure on pharmaceutical companies to crank it out along with the ordinary flu vaccine, and 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, 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.

“We’re in this race against the virus, and only Mother Nature knows how many cases are going to occur over the next six to 10 weeks,” said Michael Osterholm, a vaccine expert at the University of Minnesota.

In the meantime, many states have had to postpone mass vaccinations. Clinics around the country that managed to obtain doses of the vaccine have been swamped. And doctors are getting bombarded with calls from worried and angry parents.

“Nobody has it,” said AnnMarie O’Connor, who waited more than four hours for the vaccine in Rockville, Md., standing in line with her two young children and about 1,000 other people. Health officials “said the shots would be here in early October. But where are they?”

That’s also the case in St. Joseph, where the vaccine has been available to the segment of the population most at risk, such as young children, pregnant women and health care workers who are most likely to come into contact with patients who are infected.

In St. Joseph, shipments of the nasal spray vaccine have been available on a weekly basis. That intranasal spray is targeted to healthy 2- to 4-year-olds. The injectable vaccine was recently made available to about 500 health care workers, and other supplies have been available for pregnant women.

Health officials said the weekly shipments are about what’s expected, though they acknowledge that it’s still not possible to make the vaccine — either the injection or the nasal spray — available to the wider public.

“We’re working as fast as we can,” said Stephanie Malita, an administrative aide with the City of St. Joseph Health Department. “We are still focusing on priority groups.”

Federal officials counsel patience, saying that eventually there should be enough of both vaccines for everyone who wants them.

“We wish we had better ways to produce vaccines perfectly predictably, but this is how influenza vaccine production often goes,” Dr. Anne Schuchat, who heads the immunization and respiratory disease section at the Centers for Disease Control and Prevention, said last week.

The delays have led to renewed demands for a quicker, more reliable way of producing vaccines than the chicken egg method, which is 50-year-old technology and involves injecting the virus into eggs and allowing it to feed on the nutrients in the egg white.

Since April, the H1N1 virus has killed more than 800 people in the U.S., including 86 children.

Federal health officials initially projected that as many as 120 million doses of the vaccine would be ready to dispense by mid-October. They later reduced their estimate to 45 million. As of Tuesday, only 12.8 million were available.

The government now hopes to have about 50 million doses out by mid-November and 150 million in December, Dr. Nicole Lurie, assistant Health and Human Services secretary for preparedness, told The Associated Press on Wednesday.

The News-Press contributed to this report.