Every year, more than 36 thousand Americans die from it. Two hundred thousand will be hospitalized and 30 to 50 million adults and children will get it. It is influenza, the flu, and it is caused by a virus. Each year, the question for scientists is which virus will it be, and will taking a flu vaccine prevent you from getting it?
"It absolutely protects you," said Dr. William Schaffner of Vanderbilt Medical School.
A leading expert on infectious diseases, Schaffner says there is no universal vaccine that will protect you from the flu. Each year, health officials determine months ahead of the winter flu season which three viral strains will likely affect the most people and then create a vaccine to protect against them.
"There are places all around the world that are constantly culturing people, taking specimens from people and testing them for influenza," Dr. Schaffner said.
But what happens if a fourth strain happens to break out? Will the vaccines do us any good?
Dr. Schaffner said, "Yes and no. It is a bit of gamble. We do our best to match up what's in the vaccine with the anticipated strain and then every once in a while, we get a new strain that tries to take over."
But unlike vaccines for polio and the measles -- which are nearly 100 percent effective --the flu vaccine is 70 percent to 90 percent effective in preventing illness.
"The stronger and younger you are, the more effective the vaccine is because your immune system is more robust," he said.
"The most important question to ask is, is it good for you as an individual and is it good for the public health. And I think the answer there is a resounding yes," said Dr. Harvey Rubin, professor of medicine at the University of Pennsylvania.
Dr. Rubin added, "Another common myth is that you'll get the flu by getting the flu shot. You won't get the flu by getting the flu shot. Another common myth is that there are very serious side effects. There are very, very few side effects of the flu shot."
What about all the talk and worry about flu strains from Asia?
"The really new strains of influenza have traditionally come out of Asia. And the reason is that you have so many people so close to so many birds and so many pigs," said Dr. Schaffner.
He explained, "The influenza viruses move from the birds to the pigs to the humans and get together and that's been kind of the, the origin of new strains."
This year's vaccine will not protect you from the strain that everyone is watching, H5N1, or the deadly avian flu. There are only about 100 known cases of it passing from birds to humans, but it could create a pandemic killing millions worldwide if the virus mutates into a form easily passed from human to human.
So, how likely is it that the bird flu could break out this winter?
"To quote a friend of mine," said Schaffner, "he said we know the pandemic clock is ticking, but we don't know what time it is."
Schaffner said he thinks the chances of a mutation occurring this winter are slim, "Not zero, but very small."
Dr. Rubin was concerned about our lack of preparedness for a potential pandemic. "We're really not prepared for the magnitude of what could happen, if it happened this winter. Don't forget, the H5N1, that avian strain, has been around since '97, and fortunately it hasn't spread human-to-human yet. But it may be only a matter of time."