Swine flu wanes, but experts say pandemic strain could reemerge
By David Brown
Washington Post Staff Writer
Tuesday, February 23, 2010
Even as officials from the Centers for Disease Control and Prevention are announcing that the epidemic of the H1N1 flu is no longer widespread in any state, no disease expert is willing to say there isn’t a third — or fourth — wave of swine flu in the country’s future.
Influenza transmission waxes and wanes, and outbreaks of novel pandemic strains occur in particularly unpredictable waves that depend on such variables as human behavior, atmospheric conditions and even competition from other microbes. That places them among the bigger mysteries of epidemiology, the science of disease outbreaks.
The “Spanish flu” of 1918 had four waves of greatly differing deadliness, spread over two years. The “Asian flu” of 1957, like the current H1N1 strain, had a late-spring and a fall wave — followed by a third in late winter of 1958. It then took a year off before peaking again in 1960. The “Hong Kong flu” of 1968 had more than a year hiatus between its two waves, with the second infecting nearly as many people as the first.
“We are not at all out of the woods because the virus continues to circulate, but the chances of a very large additional wave are very hard to predict,” said Anne M. Schuchat, who is leading the government’s response to the H1N1 pandemic at the CDC.
What explains the retreat of this flu since its peak in late October? “That’s a great question, and it is still very much an open question,” said Katia Koelle, a biologist at Duke University who studies the dynamics of disease outbreaks.
