WASHINGTON -- A typical school student who catches swine flu will spread it to two to three classmates. Thursday's stark new estimate comes as U.S. officials urged people to get the old standby flu shot out of the way now -- so they're ready when swine flu shots start arriving next month.
In a confusing fall, many Americans will need to line up for at least two separate influenza vaccinations: The shot to protect against regular flu, plus another -- either one dose or two -- to protect against the new swine flu that doctors call the 2009 H1N1 strain.
Don't plan on making one trip to just get jabbed in each arm. Regular flu vaccine is widely available already in doctors' offices, clinics and retail pharmacies. But it's not clear if the exact same places will get shipments of H1N1 vaccine starting in mid-October.
And despite all the headlines about swine flu, which has become the main influenza strain circulating the world, doctors do expect some garden-variety flu to hit this fall, too -- the kind that every year kills 36,000 Americans and hospitalizes 200,000.
"This year, we are in uncharted territory," warned Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention.
There's no way to predict how much of either flu strain will circulate, although Frieden said some parts of the Southeast in the last few weeks have experienced as much flu as is usually seen in the middle of winter.
A new Associated Press-GfK poll shows the population split on whether they or their children will get the seasonal flu shot this year -- although 57 percent say they're likely to seek a swine flu shot, and 61 percent would give permission for their children to get a swine flu vaccination at school.
Hundreds of school districts are planning for in-school inoculations, a decision backed by research published in the journal Science Thursday. Based on how swine flu spread through a New York City school last April, and some other schools since, the average schoolchild with H1N1 will infect between two and three others students, said flu specialist Ira Longini of the University of Washington in Seattle.
Moreover, Longini modeled how the H1N1 strain is spreading to predict that a wave this fall could peak as early as mid-October, too late for swine flu vaccinations to have much of an impact. That's just a model, responded Dr. Anthony Fauci of the National Institutes of Health, saying the government so far is sticking with its timetable on a mid-October start to H1N1 shots.
But regular flu vaccine is here now.
"Take some individual responsibility to stay healthy during the flu season," said Health and Human Services Secretary Kathleen Sebelius, who scheduled her own seasonal shot on Friday.
Waiting to get the first inoculation out of the way "is not in anybody's best interest," added Dr. Nancy Nielsen, past president of the American Medical Association. She said busy doctors need regular vaccinations done by the time they have to deal with H1N1 shots.
And no, you can't catch the flu from a flu shot, stressed Frieden, trying to kill that long-held myth.
The CDC expects about 116 million doses of vaccine against regular winter flu this year, not quite as much as last fall's record supply. But typically only 100 million Americans seek flu vaccine, even though it's recommended for the vast majority of the population.
Who needs which vaccine? There's lots of overlap. Topping the list for regular flu vaccine:
--Adults 50 and older.
--All children age 6 months to 18 years.
--People of any age with chronic health problems like asthma, heart disease or a weakened immune system.
--Caregivers of the high-risk, including babies younger than 6 months.
Don't like shots? There's a nasal-spray version of the vaccine, called FluMist, available for people ages 2 to 49.
Once the swine flu vaccine arrives, first in line will be:
--Children starting at 6 months, up through young adulthood, age 24.
--Younger and middle-aged adults with those chronic health conditions.