Another expert agreed. "The most important unknown is the clinical severity of the illness, although the accumulating evidence is that the severity is no worse than that of the seasonal flu," said Dr. Christopher Crnich, assistant professor of medicine in the division of infectious disease at the University of Wisconsin School of Medicine and Public Health. However, "no mathematical model is going to be able to predict [severity]," Crnich added.
So far, the swine flu does not seem to have the level of sustained human-to-human transmission of a "true" pandemic, Dumyati added.
The World Health Organization recently raised its global pandemic alert to phase 5 -- just shy of the highest level possible, which is phase 6, signifying a global pandemic.
According to the WHO Rapid Pandemic Assessment Collaboration, which produced the new Science paper, the new analysis supports the phase 5 decision, and indicates a certain level of person-to-person spread.
But the hallmark of this outbreak has been the large number of unknowns -- including how virulent the virus is and how it spreads -- and that is true of this analysis as well, the authors warned.
Nevertheless, such information is necessary to inform public health decisions, experts say.
Confirmed cases of H1N1 swine flu in the United States climbed to more than 2,600 across 43 states by Monday, including three deaths, and the U.S. now surpasses Mexico as the country most affected by the outbreak, according to World Health Organization figures. The vast majority of cases remain mild, however.
So far, U.S. deaths linked to swine flu occurred in individuals with multiple underlying health problems.
On Monday, the World Health Organization was reporting 4,694 confirmed cases of swine flu in 30 countries, with Canada, Spain and the Uni
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