Swine Flu: Learning From Past Pandemics
New Flu Shares Features of Deadly Flu Pandemics
But it isn't a good idea to take the current spring outbreak lightly. Simonsen notes that the second, more severe wave of the 1889 flu pandemic swept through London in the summer months. And the 1957 flu hit the U.S. in September while there was still summer weather.
"These pandemics violate one rule after another that we think we know about flu," Simonsen says.
This fact isn't lost on the CDC.
"That is always the tricky part with influenza: You never know what we'll get until we get there," Bridges says.
Based on history, Simonsen says there are three main things to keep an eye on:
• Get a really good grip on the age distribution of severe outcomes, especially deaths, to learn which populations most need protection from antiviral drugs and vaccines.
• Test lots of people for H1N1 swine flu antibodies, so that a case-fatality rate can be calculated.
• Watch what happens in the Southern Hemisphere during its flu season.
Richard Besser, MD, acting CDC director, said at a news conference today that the CDC is actively pursuing all of these studies -- including keeping an eye on the Southern Hemisphere.
"That will tell us whether virus could return here in a form dangerous to human health," Besser said. "And if this were to come back in more severe form, we are looking to see what do we need to be able to do in our communities and at the federal level. As individuals ... think about how to make sure you are ready."
Planning ahead does not mean turning a blind eye to the present.
"Don't take your guard off things you can do right now," Besser said. "Because we are hearing from states of increased flu activity."