Swine flu or H1N1 took the country by storm last spring, and quickly rose to a global threat.
It was a pandemic health experts had planned for but still didn't see coming.
"We don't know yet how widely it's spreading and we certainly don't know the extent of the problem," said Dr. Anne Schuchat of the Centers for Disease Control and Prevention.
Swine flu started in Mexico and by late April had spread throughout the world.
Quickly followed by outbreaks in schools.
Shocked by the number of children dying from the virus some schools closed in an effort to prevent its spread.
We heard from our nation's leaders. Some messages were clear.
"This is obviously a cause for concern and requires a heightened state of alert," said President Obama.
Others confusing and quickly disputed.
"I wouldn't go anywhere in confined places now," said Vice President Joe Biden.
Another message, wash your hands, was drilled into our heads over and over.
And hand sanitizers flew off store shelves.
"I would say people should use it several times a day, three or four times a day," said internist Dr. Paul Sehdev.
It soon became clear the virus was transmitting quickly from human-to-human, leading officials at the world health organization to declare a pandemic.
Cases dropped over the summer and manufacturers made progress on an H1N1 vaccine.
"We still feel we're on track to have a vaccine ready by mid-October," said Health and Human Services Secretary Kathleen Sebelius.
But as soon as school started again swine flu cases jumped.
Widespread outbreaks caused hospital overcrowding and isolation.
And still more deaths.
By the beginning of October cases reached record levels just as the first doses of vaccine arrived.
First in line were high-risk groups.
Vaccine was scarce, forcing many to wait in long lines.
Doctors' offices were inundated with calls, especially after new CDC estimates found over 4,000 had died from the virus.
"Everybody's asking me 'where's the flu shot? When are you gonna get it?' to be honest, we almost make up dates. We just don't know," said Dr. Ira Breite.
Despite the high demand, many questioned the safety of the vaccine, putting the CDC on the defensive.
"We have cut no corners. This flu vaccine is made as flu vaccine is made each year," said Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention.
And to face heat from Congress.
By November cases started going down, more vaccine was made available and just in time for Santa.
Cases continued to decrease well into December yet experts warned we're not out of the woods yet.
The latest estimates from the CDC show 10,000 people have died from swine flu this year.
Experts stress it's important to keep up your hand-washing over the holidays when families gather they share not only the love, but also their germs.