Dr. Dennis Carroll, special adviser on pandemic flu to the U.S. Agency for International Development, noted that the 1918-1919 flu pandemic also began in the spring and was initially mild, but a much more lethal version hit six months later and the virus eventually killed 50 million worldwide.
Dr. Anne Schuchat, acting deputy director for science and program at the Centers for Disease Control and Prevention, also urged caution, saying they expected to see more people get sick and more serious cases. One factor, she said, is that the Southern Hemisphere is now moving into its flu season.
But she also stressed that "at no time in our history have we been more prepared to face this challenge."
She said the CDC moved rapidly to determine that the virus circulating in the U.S. and around the world contains genetic pieces from four different virus sources and that within two weeks it was able to understand its complete genetic characteristics.
"We have isolated and identified the virus and discussions are under way so that, should we need to manufacture a vaccine, we can work towards that goal very quickly," she said.
Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, said the CDC is currently at the stage of processing vaccine seed virus. If the need arises, they can coordinate with manufacturers on clinical trials, verifying the safety, efficacy and right dosages of the vaccine, and then move to mass production.
Schuchat said that as of Wednesday there had been 1,516 confirmed H1NI cases in 22 countries - Guatemala being the latest. Confirmed cases in the United States have reached 403, with another 702 probable cases.
CDC and World Health Organization figures show 42 deaths in Mexico and two in the United States, both in Texas.
The WHO has stopped short of declaring the outbreak a pandemic. There were three pandemics in the 20th century, the Spanish flu of 1918 that killed 50 million worldwide, the Asian flu of 1957 that killed 1-2 million and the Hong Kong flu of 1968 that killed 700,000.
Schuchat said the swine flu appears to differ from seasonal flu in that most U.S. cases, including those needing hospitalization, involve those aged five to 50 instead of the very young and the elderly. One possibility is that people older than 50 might have protection because of exposure to a similar virus when they were young, she said.
Rep. Donald Payne, D-N.J., chairman of the Africa and global health subcommittee, also expressed concern that not one case had been found in Africa. That "may actually represent the absence of the ability to detect the virus and may mean the true impact of the strain is yet to be seen," he said.
AID's Carroll said his group is working with more than 30 countries in the developing world on pandemic responses. He said some of the groundwork was laid with the U.S. investment of $543 million since 2005 to help countries monitor the spread of avian influenza virus.
RELATED INFORMATION:
FAQs about swine flu
Additional swine flu resources
Transcript of 6abc.com's swine flu chat with local experts
RELATED LINKS:
CDC Swine Flu site
World Health Organization
RELATED INTERACTIVE:
Swine flu cases around the world
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