The announcement will have a greater effect on Third World countries, freeing additional funds for treatment and prevention and helping to make stocks of antiviral drugs more readily available.
Chan said the agency had already distributed more than 5 million doses of the antiviral drug Tamiflu to 121 developing nations, which will stockpile the medicine for use "should the virus arrive at their doorstep." The agency will now begin distributing 5.65 million additional doses that have been donated by Tamiflu's manufacturer, Roche Holding of Geneva, including doses specially formulated for children.
The World Health Organization had hesitated to raise the alert level out of concern that such an announcement would be misconstrued as an indication that the virus has become more pathogenic.
The declaration "does not mean that there is any difference in the level of severity" of the virus, said Dr. Thomas R. Frieden, who became CDC director Monday. "This is not at this point a flu that is anywhere near as severe as the 1918 Spanish flu. There is no change in the behavior of the virus, only that it is spreading in more parts of the world."
In fact, all evidence to date is overwhelming that the virus is mild in its effects. About 2% of victims have been hospitalized, Chan said. Most infections have been in people younger than 25, which is a marked difference from the seasonal flu, which has its greatest effect on the elderly and frail. About one-half to two-thirds of deaths have occurred in people with chronic underlying conditions, such as respiratory problems like asthma, cardiovascular disease and autoimmune disease. Those who are obese or pregnant are also at increased risk.
Experts fear, however, that as it passes through populations, the virus could mutate to become more lethal and return with increased force in the winter influenza season. That may have been what happened with the Spanish flu, which killed millions worldwide.
"The virus writes the rules, and this one, like all influenza viruses, can change the rules, without rhyme or reason, at any time," Chan said.
Officials had previously said they feared that the announcement would lead frightened people who are not seriously ill to overrun hospital emergency rooms, impairing the healthcare system's ability to treat the truly sick. That has happened in previous outbreaks, and there is some evidence that it is happening in South America, particularly in Argentina, where the numbers of infected have been growing.
Chan and United Nations Secretary-General Ban Ki-moon urged member countries to avoid the imposition of travel restrictions, border closings and bans on imported food -- all of which have already happened in the earlier stages of the outbreak.
"We must guard against rash and discriminatory actions such as travel bans or trade restrictions," Ban told a news conference at U.N. headquarters. "Our response to any pandemic must be grounded in science."
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thomas.maugh@latimes.com
