Project scientist Zheng Xing and veterinarian and cooperative extension specialist Carol Cardona say that exposure to previous seasonal-flu viruses with similar structures, or epitopes, to H1N1 -- including H5N1 avian influenza -- is helping seniors fight off the new virus via cell-mediated immunity, not antibody-mediated immunity.

Antiviral chemicals emitted by cytotoxic T-cells may be benefiting seniors’ immune systems. This would explain why seniors have been less affected by H1N1 so far, and why avian influenza epidemics in the past have affected seniors less severely than younger people.

This discovery of the power of cell-mediated immunity could “play a key role in lowering the disease-causing ability of the 2009 H1N1 influenza,” says Xing.

The findings will be published online and in print in the journal Emerging Infectious Diseases, published by the Centers for Disease Control and Prevention.