In previous outbreaks, new infections in fall and winter were most deadly.
The rest of the world may be exhaling at the apparent easing of a potential swine flu pandemic, but some global experts are tempering their optimism with concerns about what one calls "the fall question."
That's the uncertainty over whether the current outbreak is only a preview(预告) of what's to come, an echo of previous epidemics — including the 1918 flu — that saw mild first cases of infection in the spring followed by more severe second and third bouts(发作) in the fall and winter that brought widespread infection, illness and death.
"Right now, you have to wait and watch," said Ann Marie Kimball, professor of epidemiology (流行病学)and an expert in emerging infectious disease at the University of Washington in Seattle(西雅图).