Five workers for Project Viva are huddled at a corner table at a McDonald's in Spanish Harlem, a rambling Manhattan neighborhood with such a large Latino population that the restaurant is playing Puerto Rican music for the morning's breakfast crowd. The workers are deciding which of the nearby apartment buildings they will visit today, as they go door-to-door offering free flu shots.

Fears of a shortage of flu vaccine this winter prompted U.S. health officials to limit the shots to people over 65 years old and others who are considered at high risk for influenza, the contagious disease that kills an estimated 36,000 Americans each year. While many of the restrictions have been eased, urban health experts say the vaccine may not be reaching residents of poor inner city neighborhoods.

"There has always been a disparity in health care services between the wealthy and parts of the community that are less affluent," says Kay Glidden, a research nurse with the New York Academy of Medicine, the non-profit organization that runs Project Viva.

She says the vaccination campaign is designed to head off a possible flu epidemic in communities where, her group's research indicates, health care has been chronically inadequate. "We found in our study that several neighborhoods have very poor access to medical care, and the rate of vaccination is very low among adults," Ms. Glidden says. "Facilities are not available. Transportation to get to the facilities isn't available. Insurance is almost non-existent. Or if they have families to take care of, they don't have a lot of free time to go looking for resources. So they go without."

The result, she says, is a worsening of such conditions as hypertension, diabetes and liver disease. "And then if they were infected with the flu on top of that," she notes, " the complications would be extreme and they would have to be hospitalized."

Still, not everyone will accept the free flu shots offered by Project Viva, because they are wary of strangers visiting them. "Of course, I would be...people coming to the door with yellow jackets," admits interview outreach worker Jose Sanchez. As he and the rest of the Project Viva team walk through the frigid air to their first destination, he talks about the neighborhood. "You have a lot of wheeling and dealing and goings-on with prostitution and stuff like that," he says.

"So people are suspicious," agrees Project Director Sarah Sisco. "You know, you get a knock on the door, [and] even if you see a friendly face, not everyone is going to say 'Sure, let me roll up my sleeve and let me inject you with something.' So we've taken great pains to make sure that that legitimacy is conveyed from the first second that we knock on the door."

Outside an apartment on the third floor of a badly dilapidated tenement building, Mr. Sanchez says that, in his experience, undocumented immigrants seem to be most likely to agree to a flu shot. "An immigrant is appreciative of the fact that we are coming to their door," he says. "And 'free' is the golden word here. We don't ask anything of them. All we ask is to take the simple survey, [which takes] five minutes, and they get the shot."

The anonymous survey is a key part of Project Viva. It asks people a few simple questions -- whether they are working or not, how frequently they see a doctor, whether they have AIDS. Researchers at the New York Academy of Medicine compile their answers into a database that helps the Academy target its public health outreach more effectively.

The man at the door, like many of his neighbors, agrees to take the survey and get a shot. While nurse Glidden prepares the syringe, project director Sarah Sisco observes that door-to-door health programs have proved their effectiveness time and again in poor communities outside America. "So we're really looking at that," she says, "because New York City is full of immigrants and people who don't speak English. [There are] so many different languages and cultures how do we reach those people, as well as people who may not like services that are provided in a formal way?"

Project Viva is modeled after similar projects in other countries. "In India, for example, we looked at programs that were delivering polio vaccine at the door," Ms. Sisco says. "That was something that was pretty different, I think, from many health programs that we were tending to find here in the U.S."

The bottom line for Jose Sanchez is that struggling families that might otherwise have gone without life-saving health care will get it. "Yesterday we did an 86-year-old man, God bless him, and he was happy to see us," he says. "And that makes it worthwhile."