By BETSY MCKAY
The new H1N1 swine flu may cause more-severe illness than similar seasonal strains but may spread less easily, according to preliminary findings from a study of ferrets to be published soon by Centers for Disease Control and Prevention scientists.
CDC officials said Friday they received reports of nearly 6,300 new U.S. cases in the past week, more than in any other week since the outbreak began in late April, signaling the virus isn't letting up despite summer's arrival. Almost all flu cases now tested are the new H1N1 flu rather than regular seasonal flu, the agency said.
U.S. government officials and manufacturers are preparing to produce 600 million doses of vaccine for the H1N1 virus, an effort that would dwarf seasonal-flu campaigns and would include enough for those vaccinated to receive two doses. As many as 60 million doses could be ready by September, they said at a meeting Friday of the Advisory Committee on Immunization Practices.
But federal officials haven't decided whether to go ahead definitively with the campaign, determined who would get vaccinated, or worked out logistics for carrying out a campaign alongside seasonal-flu vaccinations.
The Atlanta-based CDC has received reports of 27,717 probable and laboratory-confirmed U.S. H1N1 cases, with 127 deaths, but the agency estimates that more than one million people have had the disease in the U.S., a sign that many aren't going to a doctor or being tested for the new flu.
Many cases are mild. In addition, there are probably people who have had the virus and didn't know it because they didn't develop symptoms, said Anne Schuchat, a senior CDC respiratory diseases official. "We are expecting to see that," she said, noting that flu viruses commonly produce asymptomatic cases.
World-wide, 59,814 people in 113 countries and territories are confirmed by laboratory tests to have had the disease, and 263 have died, the World Health Organization said Friday. Those cases include a burgeoning number in the Southern Hemisphere, where flu season is getting under way.
Flu officials at the CDC and WHO are carefully monitoring large outbreaks in Australia, Argentina and Chile to see whether the virus becomes more virulent or develops resistance to antiviral drugs. The new H1N1 virus accounts for about 60% of flu cases in Australia, according to Nancy Cox, the CDC's influenza chief.
In their study of ferrets, which have respiratory systems similar to humans, CDC scientists found the new H1N1 virus could produce slightly more severe illness than a seasonal H1N1 virus, Dr. Cox said at the ACIP meeting. But the new virus didn't spread as easily from one ferret to another through respiratory droplets, suggesting it isn't as transmissible as the seasonal H1N1 strain, she said.
The study sheds a small bit of light on a virus whose unusual characteristics mystify scientists. Despite digging into their swine-flu collections in lab freezers, "no one has been able to find the predecessor" to this particular virus, Dr. Cox said. Better surveillance of pig populations is needed to track the evolution of swine flu viruses, she said.
Write to Betsy McKay at betsy.mckay@wsj.com
source: http://online.wsj.com/article/SB124606298371663817.html
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