ATLANTA — U.S. health officials say swine flu could strike up to 40 percent of Americans over the next two years and as many as several hundred thousand could die if a vaccine campaign and other measures aren’t successful.
Those estimates from the Centers for Disease Control and Prevention mean about twice the number of people who usually get sick in a normal flu season would be struck by swine flu. Officials said those projections would drop if a new vaccine is ready and widely available, as U.S. officials expect.
The U.S. may have as many as 160 million doses of swine flu vaccine available sometime in October, and U.S. tests of the new vaccine are to start shortly, federal officials said this week.
The infection estimates are based on a flu pandemic from 1957, which killed nearly 70,000 in the United States but was not as severe as the infamous Spanish flu pandemic of 1918-19. But influenza is notoriously hard to predict. The number of deaths and illnesses would drop if the pandemic peters out or if efforts to slow its spread are successful, said CDC spokesman Tom Skinner.
A CDC official said the agency came up with the estimate last month, but it was first disclosed in an interview with The Associated Press.
“Hopefully, mitigation efforts will have a big impact on future cases,” Skinner said.
In a normal flu season, about 36,000 people die from flu and its complications, according to American Medical Association estimates. Because so many more people are expected to catch the new flu, the number of deaths over two years could range from 90,000 to several hundred thousand, the CDC calculated. Again, that is if a new vaccine and other efforts fail.
The World Health Organization says as many as 2 billion people could become infected over the next two years — nearly one-third of the world population. The estimates look at potential impacts over a two-year period because past flu pandemics have occurred in waves over more than one year.
Virus impossible to predict
While manufacturers rush to develop a vaccine to stop the spread of H1N1 virus across the globe, the WHO's flu chief says the swine flu will likely mutate over a long period of time. Keiji Fukuda, WHO's Assistant Director-General for Health Security and Environment, says its impossible to predict what shape the virus may take.
"Even if we have hundreds of thousands of cases or a few millions of cases ... we're relatively early in the pandemic, "he said in an interview at WHO's headquarters in Geneva.
"We do have to be aware that there could be changes and we have to be prepared for those."
Fukuda says the virus hasn't yet shown a widespread resistance to the anti-viral drug Tamiflu, although a few scattered cases have developed .
Also Friday, the WHO said the virus is starting to infect older people, and pregnant women and the obese are at highest risk.
In a statement, the agency said school-age children remain most affected by the newly discovered virus that has been spreading fast in schools and is gaining momentum in broad communities alongside seasonal flu.
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"It remains a top priority to determine which groups of people are at highest risk of serious disease so steps to best protect them can be taken," it said, estimating that vaccine manufacturers should have H1N1 shots ready soon.
At least 50 governments worldwide have placed orders or are negotiating with pharmaceutical companies to secure supplies of vaccines against the H1N1 strain, which are still being developed and tested.
"We expect the first doses to be available for human use in early autumn of the northern hemisphere," Hartl said.
The WHO is trying to ensure that health workers in the world's poorest countries can be vaccinated against the strain so that their hospitals and medical clinics can stay open.
Rich nations have already have already pre-ordered most of the vaccine's available stock. But two manufacturers have promised to donate 150 million doses and the Geneva-based United Nations agency is negotiating with other producers for further doses which would be earmarked for the least developed countries, he said.
Hartl did not name the donor companies. Leading vaccines makers include Sanofi-Aventis, Novartis, Baxter, GlaxoSmithKline and Solvay.
It is still unclear if one or two jabs will be required for protection against the virus — a never-before-seen combination of swine, bird and human flu strains. Its emergence and international transmission caused the WHO to declare in June that a full pandemic is under way.
The Associated Press and Reuters contributed to this report