Feb. 23, 2008 -- Thanks to a particularly virulent strain of the flu, this year's flu season has been one of the worst doctors can remember.
Packed emergency rooms, empty classrooms, and bustling college infirmaries are all signs that the vaccine just isn't working as well as it has in past years.
The Centers For Disease Control says the flu is now tearing through 49 out of 50 states. That's up from 44 states last week.
"We do have a strain that is not covered in this year's flu vaccine," explained E.R. nurse Christina Miller.
This year's flu shot seems to not be effective. It doesn't match two of the three main flu bugs knocking people down. Normally the vaccine eliminates more than 70% of potential cases, but this year it's about 40 percent.
"It's not a great vaccine this year, it is not very effective," said Neil Fishman, an epidemiologist at the University of Pennsylvania.
The flu vaccine currently takes between six and nine months to be made. So when scientists were preparing the coming year's formula they have to guess which strains are going to be dominant months in advance. This year they guessed wrong.
"In the past couple of decades we've been right most years -- not all years, for sure. This year it was not right," explained Robert Crouch a Professor at Baylor College of Medicine.
The mistake doesn't just lead to fevers, coughing and sneezing. An estimated 36,000 Americans die each year from influenza.
Doctors still recommend getting the flu vaccine even if it doesn't prevent you from getting sick, because they say it will protect against more serious complications.