By Maggie Fox, Health and Science Editor WASHINGTON, Feb 1 (Reuters) - Future disease pandemics will be scored in the United States much like hurricanes, with the most severe triggering school closings and changes in the workplace, under federal guidelines issued on Thursday. They are the first detailed advice for what states and communities should do before a vaccine is available to control a flu pandemic, which global health authorities fear could come at any time. "We must be prepared to face the first wave of the next pandemic without vaccine and potentially without sufficient quantities of influenza antiviral medications," a government report on the new guidelines reads. The system, developed by the Centers for Disease Control and Prevention and the U.S. Department of Health and Human Services, ranks pandemics from Category 1 to Category 5. A Category 5 outbreak would be the worst imaginable, with a mortality rate of 2 percent, or 1.8 million deaths, in the United States alone. Such a pandemic was seen in 1918, when an estimated 50 million or more people died globally and more than 600,000 in the United States alone. A Category 1 pandemic would resemble the last flu pandemic, in 1968, with a death rate of less than than 0.1 percent and fewer than 90,000 deaths. In a normal flu season, about 36,000 people die in the United States, and 250,000 globally. Experts agree another flu pandemic is overdue. The most likely cause now is H5N1 avian influenza, which has spread to birds in more than 50 countries and which has infected 270 people worldwide since 2003, killing 164 of them. But it could evolve into a form that passes easily from person to person. Based on what they know about the virus, experts predict H5N1 has the potential to cause a serious pandemic -- Category 5 under the new definitions. "That would cause a shock equivalent to 15 Katrinas," Dr. John Bartlett, an infectious-disease expert at Johns Hopkins University in Baltimore, told reporters. Hurricane Katrina devastated the U.S. Gulf Coast in 2005. NO HELP FROM WASHINGTON It would take months to develop a vaccine, and antiviral drugs are in short supply. The U.S. federal government has said repeatedly it could not help much. The report recommends voluntary isolation of ill persons in Category 1 pandemics. For Category 2 and Category 3 pandemics, communities may consider voluntary quarantines of household members exposed to an infected person, as well as "social distancing" measures such as flexible working hours and limited school closures. In a Category 5 pandemic, schools and child-care facilities may be closed and businesses may be asked to be liberal in allowing leave. Experts said closing schools and businesses could cause more problems. "If you are going to ask somebody to stay home, what ethical obligation (do you have) to provide them with antivirals?" asked Dr. Bruce Gellin, who helps coordinate pandemic planning at the Health and Human Services department. "We also need to think about how vital medical and food supplies will reach those who are quarantined," including those on food-assistance programs, added Dr. Jeff Levi of the nonprofit Trust for America's Health.
