The flu virus is easily passed from one person to the next.
Every year, 5 to 20 percent of the American population catches a flu virus.
Symptoms are similar to those of the regular flu virus.
He became the first American to isolate human flu virus.
More recently, flu virus was isolated from a child in Colorado.
Most cold and flu viruses are spread by direct contact.
These medicines have not worked against most types of the flu virus.
Flu viruses change quickly, so each year scientists make a new vaccine.
"Some types of flu virus are just more deadly than others," he said.
They also stand a greater risk of catching the flu virus, so if you think you've got it - try to avoid them.
This year the influenza virus has once again changed to a form against which most people have no protection.
Human influenza virus had first been isolated just a few years earlier.
One in every four Americans had contracted the influenza virus.
For the last three years my interest has been influenza virus.
But it has no effect on other families of viruses, including influenza virus.
Most kinds of influenza viruses live only in birds, not people.
Look at all the thousands of years we've been trying to stamp out just one life form, the influenza viruses.
Scientists have come to expect the influenza virus to do the unexpected.
"But you hadn't counted on her being exposed to an influenza virus before she even left."
The flu, however, is caused by a much more limited number of influenza viruses.
There wasn't a flu bug in the world that could keep her in bed for three days.
The flu bug could not have come at a worse time.
United have just about shaken off the flu bug and are back to more or less full strength.
But this flu bug hasn't traveled through the house yet.
The flu bug had put the whole force on extended shifts.
Unfortunately, although a good time was had by all, a number of the team picked up a strange flu bug.
You may be infected with the flu bug but don't yet have symptoms.
"I'm not thinking straight; if he had the 1918 flu bug he'd be fiat out by now."
He hoped it was a flu bug, or even the knot on his head.
He fell ill and died of another "flu bug" in July 1919.