The United States still has no licensed vaccine to prevent avian flu and has nowhere near enough drugs on hand to treat the sick if there is an epidemic, experts told Congress on Thursday.

Hospitals have too little capacity to deal with the huge numbers of people who would become sick and the U.S. Health and Human Services Department does not even have a plan for dealing with an epidemic, the experts said.

"Although many levels of government are paying increased attention to the problem, the United States remains woefully unprepared for an influenza pandemic that could kill millions of Americans," said Dr. Andrew Pavia, chairman of the Infectious Disease Society of America´s Pandemic Influenza Task Force.

"Clearly, we need a much larger supply of drugs and vaccine to control a flu pandemic. We need to build up U.S. manufacturing capacity so that we are not dependent on other countries to meet our needs," Pavia said in remarks prepared for a hearing of the health subcommittee of the House of Representatives?Energy and Commerce Committee.

The H5N1 strain of avian flu affecting chickens, ducks and other birds in parts of Asia could sicken up to 20 percent of the world´s population if it acquires the ability to pass easily among people, says influenza expert Dr. Albert Osterhaus of the Erasmus Medical Center in Rotterdam, Netherlands.

A pandemic could throw 30 million people into the hospital and a quarter of them could die, Osterhaus and colleagues predicted in articles in Thursday´s issue of the journal Nature.

The H5N1 virus, which first surfaced in poultry in Hong Kong and China eight years ago, has killed 37 people in Vietnam, 12 in Thailand and four in Cambodia.

It does not yet easily infect people but if it mutates just a bit, it could rival the 1918 Spanish flu pandemic that killed between 20 and 40 million people.

Influenza causes epidemics annually and kills 36,000 Americans in a normal season. Different strains emerge almost annually, and a new one can kill many more if it is one that has not affected people in recent years.

A brand-new strain could be devastating.

"The U.S. population has no immunity and therefore no protection against this deadly virus," Pavia said.

He recommended that the United States stockpile a larger supply of antiviral drugs, especially oseltamivir, made by Switzerland´s Roche under the brand name Tamiflu. Avian influenza resists older antiviral drugs such as amantadine and rimantadine but Tamiflu can help make an infection less severe.

Although Roche has quadrupled its production capacity for Tamiflu, experts believe global stockpiles will be too small for a pandemic. The current stockpile would treat less than 2 percent of the U.S. population -- Pavia said IDSA recommends having enough on hand to treat 50 percent.

The U.S. government has also contracted with Sanofi-Aventis and Chiron Corp. to make H5N1 flu vaccines, but the contracts provide for only 2 million doses and the vaccines are still experimental.

The U.S. Government Accountability Office also criticized the U.S. lack of preparation.

Marcia Crosse, Director of Health Care for the GAO, said in prepared testimony that the United States needs to address regulatory, privacy, and procedural issues surrounding measures to control the spread of disease, especially across borders.

And the hospital and health work force is insufficient to handle an influenza pandemic, she said.