Younger People Appear More at Risk From New Swine Flu

Another article in the journal, from researchers at the U.S. National Institutes of Health, compares the new H1N1 flu to the deadly 1918 flu, which killed between 20 million and 40 million people worldwide, including 500,000 in the United States.

"The 1918-1919 influenza pandemic was a defining event in the history of public health," co-author Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said in a prepared statement. "The legacy of that pandemic lives on in many ways, including the fact that the descendants of the 1918 virus have continued to circulate for nine decades."

The authors say that descendants of the 1918 flu, which include the new H1N1 strain, have genetically modified themselves to be better able to survive and spread. To do this, they have become less severe so as not to kill their host, making it easier to spread from person to person.

A final report in the journal is from researchers at the U.S. Naval Health Research Center in San Diego and the U.S. Centers for Disease Control and Prevention, who developed a rapid test to diagnose the new H1N1 swine flu.

They note that although the test was effective in finding the first cases of the strain in the United States, their test and others like it must be constantly updated to keep up with changes in this and other influenza strains.

In the case of resistance to Tamiflu reported Monday by Danish officials, the person reportedly was taking the drug because of believed exposure to swine flu but developed the disease anyway.

A representative of Roche, which makes Tamiflu, said in a teleconference with journalists that such a development was not unexpected.

Officials said the person who'd contracted swine flu had recovered.

More information

The U.S. Centers for Disease Control and Prevention have more on swine flu.