"We believe it's important that all people be vaccinated regardless of immigration status," says Jon Feere, legal policy analyst at the Center for Immigration Studies, which opposes taxpayer-funded health care for illegal immigrants and wants to reduce immigration.

Leaving 10 million to 12 million immigrants unvaccinated against the H1N1 virus, known as swine flu, would increase the risk to everyone and make it much harder to control a pandemic, says Kevin Fiscella, associate professor at theUniversity of Rochester School of Medicine and Dentistry in New York. "We're all in this together," he says.

The swine flu virus is expected to hit children, teens and young adults especially hard — a vulnerability compounded by the fact that the immigrant population tends to be younger overall than the general population.

But experts say state and local governments will have to overcome barriers to persuade illegal immigrants to trust public health departments enough to come forward and be vaccinated.

"For an undocumented immigrant who lives in daily fear of being deported, contact with any quasi-governmental agency, even a public health department, induces anxiety," Fiscella says.

Federal health officials are trying to quell those fears.

"Whether you're legal or illegal, the flu virus doesn't discriminate and neither do we," says Arleen Porcell of theCenters for Disease Control and Prevention. But the same recommendations to states for who should be vaccinated first (such as pregnant women, health care workers, and young people) would apply to immigrants too, she says.

To get that message out, Porcell says, the CDC is working with Hispanic medi