H1N1 swine flu likely will be the dominate flu strain this year, out-competing seasonal flu and infecting as many as one-third of Americans, according to Anthony Fauci, the federal government's top infectious disease expert.
"This is a virus that spreads absolutely as efficiently as a virus can spread," Fauci said in a meeting Thursday with the Milwaukee Journal Sentinel and other reporters.
The good news is that while the virus spreads easily, it produces mild disease in most people, said Fauci, head of the National Institute of Allergy and Infectious Disease. So far, the death rate has been less than 0.1 percent, he said.
In estimating that one-third of the population may get infected with H1N1 swine flu, Fauci said that in a typical year seasonal flu infects 5 percent to 20 percent of Americans.
On Friday, officials with the U.S. Centers for Disease Control and Prevention said this year's flu season has started much earlier than usual with H1N1 cases in all 50 states and being widespread in 21 states.
Nearly twice as many people are showing up at clinics than in a typical flu season, said Daniel Jernigan, deputy director of the CDC's flu division.
"It's a very strange thing to see that amount of influenza this time of year," he said.
That raises the possibility that significant numbers of people may be exposed to the virus before the vaccine is available.
The federal government has ordered 195 million doses, including the first 3.4 million doses that will be delivered the first week of October. Most of those doses will be nasal spray vaccine, not the injectable type. The nasal spray can be used in people aged 2 to 49, but it is not supposed to be used in some of the high risk groups who should be among the first vaccinated against H1N1, including pregnant women, those younger than 2, and people with a medical condition that place them at higher risk for complications from the flu.
After the initial 3.4 million doses as many as 20 million doses will be delivered each week into December to nearly 90,000 sites such as clinics and schools.
Recent tests indicate that one dose will be effective in people over the age of 10, although those under 10 may need two doses.
People who already have been infected by the virus, including those who got it in the spring, likely will have substantial immunity, but they need to know if they had confirmed H1N1 flu, officials said.
Also, anti-viral drugs such as Tamiflu are proving to be effective in treating people infected with H1N1 swine flu, Jernigan said.
Jernigan said children and young adults are being hit the hardest by H1N1 swine flu and that is likely to continue as it becomes the dominate flu strain circulating this fall and winter.
"We will have some hospitalizations and some deaths," he said.
He said he expects to see a growing number of infections now that children are back in school.
At the same time, there have been relatively few cases in older people, who are usually among the hardest hit. That's because they likely have some immunity from exposure to similar flu strains in years past, Fauci said.
"It's exactly the opposite of what you see with seasonal flu," he said.
Fauci said pandemic flus such as H1NI tend to push out seasonal flu strains.
"If we get deluged with H1N1 flu, there is a good chance it will crowd out seasonal flu," he said.
Still, health officials encouraged people to get a seasonal flu shot as well the H1N1 vaccine.
Fauci said H1N1 swine flu likely had been circulating in pigs for up to 10 years before jumping to people.
He noted that most of the more than 300 infectious diseases in humans in recent decades originated in animals.
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