U.S. Considers Massive Swine Flu Vaccinati...(rld Health Organization said Thursday th...),Health

Health officials are closely monitoring the H1N1 swine flu virus as it migrates from the Northern Hemisphere to the Southern Hemisphere, where the flu season is now under way. Scientists are concerned the virus could mutate as it circulates around the world, becoming more virulent and posing a greater health threat.

"The virus is not mutating for the moment, it is stable," Margaret Chan, director general of the World Health Organization, said in Moscow, according to Agence France Press, citing Russian news agency reports.

Still, Chan underscored the need to closely monitor the virus' spread around the globe, adding that it was highly "unpredictable."

The WHO last week formally declared a pandemic, triggered by the rapid spread of the H1N1 virus across North America, Australia, South America, Europe and regions beyond.

What makes the H1N1 strain different from the typical seasonal flu is that about half of the people killed worldwide were young and previously healthy. In contrast, regular forms of the seasonal flu typically prove most lethal to the very young and the elderly.

Even though H1N1 swine flu infections continue to be mild, for the most part, health-care workers need to do more to protect themselves from infection by the virus. A small sample of 26 health-care workers found that half became infected while at work, according to a report in the June 19 issue of the CDC's Morbidity and Mortality Weekly Report.

"This includes one case where the exposure was to another ill health-care person," Dr. Michael Bell, the CDC's associate director for infection control, said during a June 18 press conference.

Bell said infection-control procedures need to be taken seriously.

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