Hundreds of thousands of Americans could die over the next two years if the vaccine and other control measures for the new H1N1 influenza are not effective, and, at the pandemic's peak, as much as 40% of the workforce could be affected, according to new estimates from the Centers for Disease Control and Prevention.
That is admittedly a worst-case scenario that the federal agency says it doesn't expect to occur.
But the broad range of potential deaths highlights the unpredictability of flu viruses in general and this swine flu virus in particular because it hasn't behaved the way researchers have expected.
The number of potential deaths is much higher than that usually seen in seasonal flu, which kills an estimated 36,000 Americans a year, and is even higher than the nation's most recent pandemic.
A 2003 CDC study of deaths in the preceding decade showed yearly totals ranging from 17,000 to 52,000. The 1957 pandemic of Asian flu killed 70,000.
The vaccine the CDC is counting on is not expected to be available before the end of September, too late to immunize children before the start of school, where the proximity of children is expected to speed up transmission of the virus.
But testing of the vaccine has already begun at some sites, and authorities have no reason to believe it will fail because the technology for flu vaccines has been thoroughly demonstrated.
Rather, the questions have been about how long it will take to produce a new vaccine and how many doses will be available.
So far, the CDC has given no estimate of how many deaths might occur if the vaccine works.
The new estimates, prepared more than a month ago but released only Friday to the Associated Press, are not based on an enhanced lethality of the new H1N1 virus, but rather on the lack of resistance to the virus in the general population and its continuing spread through the summer months, when flu viruses normally are less active.
Twenty states are now reporting widespread or regional flu activity, with the H1N1 virus predominating, according to Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases. "That's very unusual at this time of year," she said. "It's a testament to how susceptible people are to the virus."
Cases this summer have been concentrated in camps and military installations where young people are gathered. "This has been a challenging summer for camps, with a lot of outbreaks" and closures, Schuchat said.
