Federal health officials on Wednesday predicted it will take four or five years to meet their goal of licensing a new domestically produced influenza vaccine that could be administered to all Americans in the first six months of a flu pandemic. They also acknowledged that travel restrictions could be imposed if there is such a global medical crisis, and said U.S. health and medical capabilities could be "overwhelmed." The predictions are included in a new report from the Department of Health and Human Services (HHS) that outlines the national strategy for confronting a pandemic that would result if a new flu virus emerges that can infect humans and be transmitted easily from person to person. The virus causing the most concern is the avian flu virus-the H5N1 strain-which has killed 62 persons in four Asian countries in the past two years. President Bush, who announced on Tuesday the government's $7.1 billion plan to combat a possible flu pandemic, said the main goal of the national strategy is to have enough vaccine on hand-about 300 million doses-to immunize every American within six months of the start of a pandemic. But at a congressional hearing yesterday, HHS Secretary Michael Leavitt said: "The good news is we have a vaccine. ... The bad news is ... we lack the ability to manufacture it in sufficient volumes at this time." Asked how long it would take to reach that level of preparedness, he said: "We're optimistic we could have a vaccine licensed in the next four or five years." A section of the report called "Managing Travel-Related Risks of Disease" provides recommendations to state and local governments on "travel-related containment strategies that can be used during different phases of an influenza pandemic." Such strategies range from distribution of travel health-alert notices to isolation and quarantine of new arrivals to restriction or cancellation of nonessential travel. Meanwhile, doctors are worried that a mass quarantine from avian flu could cause them ethical problems. The American Medical Association's policy-making House of Delegates, meeting in Dallas this weekend, will consider recommendations to guide physicians in the event of a quarantine.