U.S. health authorities are turning to social networking sites such as Facebook and Twitter in a bid to prepare people to be vaccinated against the pandemic H1N1 virus.

But efforts to distribute accurate information about the dangers of swine flu and the importance of vaccination are hampered by the sheer complexity of the message that the U.S. Centers for Disease Control and Prevention aims to convey.

For a start, the vaccine will not be ready for widespread distribution until mid-October, after the traditional flu season has begun.

The U.S. government hopes to target around 50 percent of the population for vaccination, focusing on key groups including pregnant women and healthcare workers.

But anyone getting vaccinated will likely need three separate inoculations: one for seasonal flu, which kills around 36,000 people annually in the United States, and two for H1N1 taken three weeks apart.

Health officials also face the problem of how to prepare the public for the onset of a disease that has killed and could kill more but has so far been largely mild.

The messages can be complicated, said Kris Sheedy, a communications director with CDC's National Center for Immunization and Respiratory Diseases.

On its CDCFlu feed at www.twitter.com, the organization sporadically posts information on swine flu death tolls and also promotes its offerings on other social media, such as an interview on YouTube with a leading CDC scientist.

The CDC Facebook page, which has more than 20,000 fans, includes information on how to prepare for swine flu and a lively discussion in its comments section.

Aside from social media, CDC has run focus groups in Chicago, New York and Atlanta in a bid to test appropriate messages and has also worked with so-called mommy bloggers, an influential group among women.

'ONLY THING CERTAIN IS UNCERTAINTY'

H1N1 is expected to surge this fall in the United States as the school year starts. The World Health Organization predicts that 2 billion people globally will likely become infected eventually.

CDC director Dr. Thomas Frieden says the new H1N1 flu is the agency's No. 1 priority.

We have literally mobilized more than 1,000 people at CDC to work on H1N1, he said.

The message to the public can be subtle and confusing, Frieden said.

If you get sick and you get a fever get help promptly. But don't overwhelm the emergency department with people who are not very sick, Frieden said.

CDC officials have been urged to admit when they do not know something.

The only thing that is certain is uncertainty, Frieden added.

The CDC is also aware that some people doubt the safety of vaccines.

People do have some trust issues. That's 2009. At CDC we are really committed to accurate, timely information, said the CDC's Dr. Anne Schuchat, director of the respiratory disease section.

Vaccine safety groups argue that insufficient testing of swine flu vaccine could pose a risk to the public and say individuals will have little legal recourse if problems emerge.

But paradoxically, public interest in the pandemic offers a chance to present concerns about vaccinations to a wider public, said Barbara Fisher, president of the National Vaccine Information Center.

It seems irresponsible to advocate and promote a vaccine and have no safety net whatsoever, and so yes it seems like an opportunity to point to some of the problems, said Fisher, a longtime critic of public vaccination programs.

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