One of the biggest fears has been that the virus, which first appeared in April in the U.S. and Mexico and which people don't have any built-up immunity to, might mutate into an even more dangerous form. Health officials have been keeping a close watch on the Southern Hemisphere, which is in its winter season now, to see what form of the virus is likely to travel north as fall comes to the U.S. and the rest of the Northern Hemisphere.
Flu viruses are unpredictable, so the fact that this one hasn't mutated is "somewhat reassuring" said Jay Butler, director of CDC's H1N1 Vaccine Task Force.
Case numbers in the Southern Hemisphere appear to be dropping, he said.
The H1N1 flu, commonly known as swine flu, continues to disproportionately affect young people, which is very different than most influenza strains. Thus far about 75% of hospitalizations and 60% of deaths are in people under 49 years, he reported.
Two states, Alaska and Maine, are currently reporting widespread influenza activity, very unusual for this time of year. Why those are being hit right now isn't known.
"It's one of the mysteries of influenza," Butler says. He did note that Alaska was one of the last states to have laboratory confirmed cases of the H1N1 strain, so it's possible the outbreak there just got a later start.
Flu vaccine production and testing is currently underway. Jesse Goodman, chief scientist and deputy commissioner with the Food and Drug Administration said that they expect to have 45 to 52 million doses of vaccine available by mid-October. They'll then be making more vaccine available weekly, up to about 195 million doses by the end of the year. Five manufacturers are working on producing the vaccine.
Vaccine will be made available to each state according to its population, Goodman said.
Testing of the vaccine to find out how much needs to be given and whether one or two doses is required is well underway in adults, with the first results expected by mid September, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
Researchers waited to make sure the vaccine was safe in adults before beginning testing in children, which got started in the past few weeks. Those results should begin coming in by mid-October.
All together over 4,600 people will be enrolled in the trials, Fauci said.
Today in Beijing, World Health Organization Western Pacific director Shin Young-soo said that cases in the Northern Hemisphere will soon begin to increase and most countries may see swine flu cases double every three to four days for several months until peak transmission is reached.
"At a certain point, there will seem to be an explosion in case numbers," Shin told a symposium of health officials and experts."It is certain there will be more cases and more deaths."
Fauci cautioned that while the CDC and FDA are preparing for worse case scenarios, "explosion" might be overstating the problem.
"Sometimes words that are used in an innocent way can cause alarm. I think in a realistic setting we should expect that there clearly is going to be an upsurge of cases when you get into the fall."
Whether or not they get vaccinated, people need to remember the three rules of staying healthy, Butler says.
"We can't stop the tide of flu any more than we can turn a hurricane in its course or stop the earth from shaking in an earthquake," he said. But we can cut down on illness. "Wash your hands, cover your cough and stay home is you're sick."
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