As of Oct. 1, the Department of Health and Human Services reported 1,378,200 doses of the nasal-spray vaccine had been ordered in 46 states and the District of Columbia.
Here is a look at some of the predicted costs associated with fighting the outbreak:
Congress appropriated $7.65 billion in June to fight pandemic flu, including H1N1. Of that, $6.15 billion has been spent or is set aside, most of it for vaccine purchases and related supplies, including syringes, needles, antivirals and other support.
Federal officials and the White House warned last spring that closing schools might be an option to contain a peak outbreak, but the CDC and other agencies now say that's unlikely.
The Brookings Institute looked at the cost of closing schools in a recent report, finding it could cost between $35 and $157 per student.
If schools throughout the country closed for four consecutive weeks, the report predicts a loss of $10 to $47 billion in economic activity, or 0.1 to 0.3 percent of GDP.
With children out of school, parents would have to find ways to work from home or take time off. Some of those parents would be health care workers, further straining the health care system.
The United States could lose about 10 percent of all work-hours, based on the number of households with at least one child and no stay-at-home adults, 23 percent. Just over half of those workers will miss some work to care for children who would otherwise be at school.
"The CDC's viewpoint is that healthy kids need to be at school. Sick kids need to be at home," said CDC spokesman Joe Quimby.
Closing schools, he added, is ultimately a local decision.
In April, the Congressional Budget Office examined the possible price tag of a national, but "mild" pandemic that sickens 75 million and kills 100,000 people, akin to the 1957 and 1968 influenza outbreaks. The office predicted a 1 percent drop in GDP, relative to what it would have otherwise been.
In the case of a "more severe" scenario, something on a scale of the 1918-19 Spanish influenza that would infect 90 million and kill 2 million people, the CBO predicts real GDP would be 4 to 4.5 percent lower.
The Obama administration's advisory group on Science and Technology predicted in August that the H1N1 virus could cause between 30,000 and 90,000 deaths in the United States this flu season. A typical seasonal flu kills between 30,000 and 40,000 each year.
According to the CDC, more than one million Americans have been infected with H1N1, and around 20,000 have been hospitalized. At least 600 people in the U.S. have died from the disease this year.