(USA TODAY) -- Vaccine for the H1N1 flu will begin arriving in the nation's hospitals, clinics and schools as early as Tuesday, the start of an effort to protect Americans against a swine flu virus that emerged this past spring and quickly circled the globe.

Thomas Frieden, director of the Centers for Disease Control and Prevention, says the effort ushers in a "challenging few weeks" for health officials.

That's an understatement.

In a task worthy of a deadly serious video game, state health departments have to organize thousands of workers at 90,000 sites nationwide to administer as many as 250 million doses in three to four months, making sure the people at greatest risk from swine flu -- such as pregnant women, young children and health care workers -- are first in line.

On top of the logistics, health officials have to convince a somewhat skeptical public that swine flu vaccinations are necessary.

And they've got to do it in the midst of vaccinating the public for seasonal flu, which by itself claims 36,000 lives across the USA each year.

"We're looking at vaccinating as many people as we can in as short a period as we can," Frieden says. "There are enormous logistical challenges."

Vaccine makers have taken about five months to get the H1N1 vaccine ready. Typically, seasonal flu vaccine takes at least a month longer but protects against three flu strains; the H1N1 protects against only one.

Officials are expecting 200 million doses by the end of the year and 50 million more by the end of April. The vaccine is coming out in 6 million- to 20 million-dose segments, so not everyone will be able to get it immediately.

"We'll be focusing initially on the high-risk groups," says Susan Smith of the Florida Department of Public Health in Tallahassee. "The vaccine will come in batches; we'll focus on pregnant women and then go down the list, based on priority."

As of late August, 100 pregnant women in the USA who contracted H1N1 required intensive-care hospitalization, and 28 died, says Anne Schuchat of the CDC's National Center for Immunization and Respiratory Diseases.

A 'bumpy' process

For each wave of vaccine that arrives, decisions about where it goes and who gets it will have to be made.

"People have to realize how fluid this is," says Paul Jarris, executive director of the Association of State and Territorial Health Officials.

The decisions will be made by state and local health officials. Most states are planning extensive information campaigns in several languages to get the word out when vaccine is available.

Even hospitals will have to dole out the vaccine carefully, because they initially won't get enough for their entire staffs. "So they'll make decisions" about who's vaccinated first, says Gregory Poland, an infectious-diseases specialist at the Mayo Clinic in Rochester, Minn. "It's reasonable that the nurse who works in the neonatal ICU will get it first and someone in dietary services will get it later."

Meanwhile, health officials have a delicate balancing act: convince those reluctant to get vaccinated that H1N1 is a real threat while making sure those most vulnerable get first shot at the vaccine at a time when supplies will be most limited.

The CDC decided to get what vaccine was available out as soon as possible, knowing things would get "a little bumpy," Frieden says.

It was "a dilemma," he says. "The choice was between having it stack up in warehouses or getting it out."

Each state has spent the past few months creating lists of possible vaccination sites, generally public health departments, clinics, hospitals, schools, private physician offices and pharmacies.

The states also are doing a lot of double-checking, says California state immunization branch chief John Talarico. "We ask for medical license numbers and we actually verify that, so we know who we're sending this to," he says. "And we might ask a local public health department why they're asking for 36,000 doses of vaccine when they've only got 500 clients."

The CDC wants vaccine to go to those most at risk first, but it isn't asking the states to require proof that someone's pregnant or has asthma. Instead, states are allowing people to "self-verify," Talarico says.

"The folks who are at actual clinics, the ones who are going to be putting the vaccine in people's arms and the FluMist up their nose," all signed a provider agreement saying they would focus initially on vaccinating people in the target groups, says Amy Caruso of the immunization branch of the North Carolina Department of Health and Human Services. But in the end, "I don't think they're going to turn anyone away from a clinic," she says.

To comply with the CDC's guidelines, states are targeting vaccinations where they're most likely to reach high-risk populations. In California, that means making sure OB/GYN clinics get ample supplies, Talarico says.

Even areas that had lots of flu last spring still need vaccine, Frieden says. In New York City, as many as 10% of people had it, but "that means that 90% of people" still need to be vaccinated.

No matter how much health officials tout the vaccine as safe -- "It's 1,000 times safer than getting the flu," says John Bartlett, director of the Center for Civilian Biodefense Strategies at Johns Hopkins School of Public Health -- some people remain fearful.

A poll released Wednesday by Consumer Reports magazine indicates that only 34% of American adults plan to get vaccinated for H1N1 when the shots become available, and only 35% of parents say they plan to have their children vaccinated.

"I'm a believer in vaccines," says Julia Getzelman, a pediatrician in San Francisco. But she's cautious about recommending H1N1 shots for her patients.

"I want to look at the risk profile of the particular child and the particular family when I talk about the benefits and potential risks of the vaccine," she says. Her concern, she says, is that there isn't enough data about the new vaccine.

Another concern she has is the already "intense" vaccination schedule for children. Kids under 9 all require two doses of seasonal flu vaccine one month apart to get full protection the first time they are vaccinated, and the H1N1 vaccine adds two more shots. "That means four pokes in a few months," Getzelman says.

CDC: Vaccine is safe

At a news conference Thursday, the CDC's Schuchat emphasized that safety is a top priority in producing and administering the swine flu vaccine.

"What I want people to know is that no corners have been cut," Schuchat says. "The H1N1 vaccine is being produced exactly the same way the seasonal flu vaccines were produced with exactly the same oversight. We've gone an additional step with that and are doing extra clinical trials, and those clinical trials so far have not found any red flags in terms of safety."

Besides children, another group of particular concern to health officials are health workers, who have notoriously low rates of flu vaccination. Only about 40% are vaccinated each year for seasonal flu, according to the CDC, despite recommendations by the Healthcare Infection Control Practices Advisory Committee that those rates be increased to 60% by 2010 to protect patients and help keep health care workers functioning during flu outbreaks.

This summer, New York passed a law requiring all health workers to be immunized against seasonal flu and H1N1, a requirement some workers have opposed. The policy is being investigated by health care worker unions.

The MedStar Health Network, which covers Maryland and Washington, D.C., began requiring that all 25,000 of its employees get the seasonal flu vaccine in August. But it hasn't required the H1N1 vaccine yet because it's awaiting more information about the vaccine's safety, efficacy and availability, spokeswoman Denise Hobik says.

Other medical centers in West Virginia, Washington state and Illinois also have made seasonal flu vaccinations mandatory for employees and are considering the same for the H1N1 vaccine.

Already, a small H1N1 vaccine resistance movement has begun online, mostly arguing against mandatory mass vaccinations. Federal and state health officials are unanimous in saying vaccinations are voluntary.

For 99 out of 100 healthy people, contracting H1N1 will lead to a fairly mild illness. But one in 100 healthy people with swine flu will end up in an intensive care unit on a respirator -- and so far doctors have no way of telling who that will be, Bartlett says.

The only protection against being that unlucky one in 100, he says, is this: Get vaccinated.

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