Novel H1N1 Continues to Wallop Younger U.S. Population

Jon is a staff writer for Science.

A new analysis from the U.S. Centers for Disease Control and Prevention (CDC) of severe disease caused by the novel H1N1 virus again emphasizes that people under 65 suffer the bulk of hospitalizations and deaths from the virus. This is exactly the opposite pattern seen with seasonal influenza, which primarily causes severe disease in the elderly.

Anne Schuchat, director of CDC’s National Center for Immunization and Respiratory Diseases, said they have analyzed hospital data and deaths from more than two dozen states between 1 September and 10 October. The study of 4958 hospitalizations found that 53% occurred in people under 25 years of age, and 39% in the 25 to 64 age bracket. The elderly accounted for just 7% of hospitalizations and 11.6% of deaths. The bulk of the 292 deaths, 65%, in this study period were in the 25 to 64 group, with young people accounting for the balance. “This is dramatically different than what we see with seasonal flu,” Schuchat said at a press conference today.

Researchers at CDC and elsewhere have shown that the elderly have some immunity to swine flu from influenza viruses that circulated before 1950 or so. But many questions remain about why the virus selectively causes such severe disease in younger people and in pregnant women. She emphasized that physicians should treat severely ill patients with antiviral flu medications even if they test negative for the virus on rapid tests. “The accuracy of the rapid tests when they show up a negative is not that good,” said Schuchat.

The vaccine against the swine flu virus, the best known protection from the disease, is still in short supply, Schuchat said. As of yesterday, states had ordered about 85% of the 12.8 million doses that CDC now has available. Schuchat acknowledged the growing concerns that this wave of the pandemic may be peaking now, suggesting that most people in the country won't benefit from the vaccine. But she stressed that there may be more waves of spread before this virus goes into hibernation. During the 1957–58 U.S. pandemic, she noted, the fall wave was followed by one that spring. “We don't want to let our guard down too soon on this,” said Schuchat.

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