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.