Most People Immune to H1N1 Flu

Here’s article about H1N1.

Swine flu no longer represents a major threat in the United States because so many people are immune to the virus that caused last season's pandemic, health officials said.

Of the 310 million people in the United States, 59 percent are believed to be immune to pandemic H1N1 flu, the researchers said. About 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 to similar viruses that circulated years ago.

"It's very unlikely that the virus will explode in the fall," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, or NIAID, an author of the analysis. "We now have evidence of that."

The evidence comes from a flurry of studies of the 2009-10 pandemic carried out by the Centers for Disease Control and Prevention, the researchers said. If this virus follows the pattern set by earlier flu bugs, it will die out completely or circulate among people who still are susceptible a year and a half after the virus emerged, the authors report in the journal mBio.

There still are many people who are vulnerable to swine flu, said David Morens, a virologist and historian at NIAID who co-wrote the report with Fauci and colleague Jeffery Taubenberger. "Even with the majority of people in the U.S. immune to the virus, that leaves many tens of millions of people still susceptible," Morens said. "We know the age groups that are most susceptible - people younger than 55 and those with chronic conditions."

The CDC estimates the 2009 H1N1 flu killed about 12,500 and sent 274,000 people to the hospital with respiratory diseases and other complications, a toll that mirrors the latest averages for people who suffer from seasonal flu. The death rate was relatively low compared with other pandemics, especially the 1918 flu, which killed 675,000 people in the United States, Morens said.

So far, he said, the virus hasn't developed "some terrible new mutation" that would make it more lethal, though that still could occur.

For the first time, federal health officials recommend that all people older than 6 months get vaccinated against flu, unless they have an allergy to eggs.