The nasty H1N1 virus that caused a pandemic last flu season will not pose a major threat this upcoming season after researchers determine an estimated 59% of Americans are believed to be immune to it.

Approximately 62 million people were vaccinated against the virus, 61 million people were infected by it, and another 60 million people 57 or older carry protective antibodies against similar viruses that date back to previous pandemics.

The federal Centers for Disease Control and Prevention recommend everyone over 6 months old get vaccinated. This year’s flu vaccine includes a dead form of the H1N1 virus.This year's vaccine also protects against the H3N2 virus and Influenza B strains.

The virus will either die out completely or continue to circulate in the decreasing pool of people still susceptible to it, the researchers concluded after examining evidence from the 2009-2010 pandemic carried out by the Centers for Disease Control and Prevention. If this virus follows the pattern set by earlier flu bugs.

The virus can still strike many as it mutates. "Even with the majority of people in the U.S. immune to the virus, that leaves many tens of millions of people still susceptible,” says co-author David Morens, a virologist and historian at the National Institute of Allergy and Infectious Diseases."Influenza viruses are mutating all the time," Morens added.

However this particular H1N1 strain is likely to "do it in small sequential steps that will be nothing dramatic, won't cause a big epidemic and, we hope, won't cause a lot of deaths,” he added.

H1N1 strain is being included in this year's flu vaccine, the portion of the population that has immunity is likely to expand, Morens added. The injected vaccine includes a dead form of the H1N1 virus.