(NaturalNews) Despite all the panic and hype about the H1N1 pandemic and the rush to immunize people in droves against the virus, the fact is -- so far -- the outbreak has been fairly mild. Now University of California (UC) Davis, researchers studying H1N1, formerly referred to as "swine flu," have identified a group of immunologically important sites called epitopes in the virus that are also present in seasonal flu viruses, which have been circulating for untold years. So what does this mean? If you were exposed to the earlier influenza viruses, you probably already have some level of immunity to H1N1.

The new study would explain why so many people over the age of 60 -- whose bodies were likely exposed to similar flu viruses over the decades -- have been found to carry antibodies or other kinds of immunity against H1N1. In fact, the CDC now admits pre-existing antibodies against the virus are found in about one third of H1N1 2009 patients over the age of 60, a fact that shows some natural immunity to the new H1N1 virus exists in many people.

"These findings indicate that human populations may have some level of existing immunity to the pandemic H1N1 influenza and may explain why the 2009 H1N1-related symptoms have been generally mild," researcher Carol Cardona, a veterinarian and Cooperative Extension specialist at the UC Davis School of Veterinary Medicine, said in a media statement.

Cardona and UC scientist Zheng Xing recently posted their findings online in the journal of Emerging Infectious Diseases. The study is also slated for publication in the November print edition of the journal, which is published by the Centers for Disease Control and Prevention (CDC). "Our hypothesis, based on the application of data collected by other researchers, suggests that cell-mediated immunity, as opposed to antibody-mediated immunity, may play a key role in lowering the disease-causing ability, or pathogenicity, of the 2009 H1N1 influenza," Xing said in the media release.

Curiously, the new research suggests that although previous similar flu viruses seem to have produced antibodies in exposed people, these antibodies are not what are providing protection for those infected with the H1N1 2009 strain of influenza. Instead, Cardona and Xing theorize that instead of stimulating protective antibodies, the epitopes of the new H1N1 virus produce an immune response in a different way. The virus triggers production of cytotoxic T-cells that kill infected cells, attack the invading virus, and rev up the immune system.