The flu has spread to 47 states, making the outbreak an epidemic. But there are some early indicators that the number of flu cases may have peaked in some parts of the country, federal health officials said.
Five fewer states reported high flu activity levels in the first week of January than the 29 that reported high activity levels in the last week of December, according to the Centers for Disease Control and Prevention's weekly flu report. This week, 24 states reported high illness levels, 16 reported moderate levels, five reported low levels and one reported minimal levels, suggesting that the flu season peaked in the last week of December.
Click here to see how this flu season stacks up against other years.
Despite the glimmer of good news, CDC officials said the virus could still make a comeback in the final weeks of the season and urged Americans to make sure they get flu shots.
"It's not surprising. Influenza ebbs and flows during the flu season," Dr. Thomas Frieden, director of the CDC, said in a Friday morning teleconference. "The only thing predictable about the flu is that it is unpredictable."
An early CDC study found this year's vaccine had an efficacy of 62 percent, making the preventive shot only moderately effective.
Although 130 million dosages of the vaccine were distributed, there have been reports of spot shortages across the country.
A Rite Aid store in Brooklyn, N.Y., told ABC News Radio it may not have enough dosages to last through the heightened weekend demand.
With a few phone calls or some online research, officials said people seeking the vaccine should be able to find a provider within a relatively close distance of their homes.
One helpful tool is the HealthMap Vaccine Finder, which includes 40,000 locations across the United States and allows users to enter their ZIP codes to find a nearby provider of the flu vaccine.
Click here to read about how flu has little to do with cold weather.
"We don't know when this is going to end. This could be the worst flu in a decade," said Dr. Richard Besser, ABC News' chief health and medical editor.
When deciding whether to stay home from work or seek medical attention, Besser said there is a key difference between the common cold and influenza.
"If you think about a cold, it usually affects you from the neck up -- congestion, sinus fullness, sore throat," Besser said. "But the flu is going to affect your whole body. You're going to feel achy all over."