Each year in the U.S. between 5 to 20 percent of the population contracts the seasonal flu. Most people recover in a few days but in extreme cases, the flu can lead to pneumonia or death. About 36,000 Americans die and 200,000 are hospitalized from the flu each year.

As far as H1N1, the CDC estimates that as many as 84 million infections occurred in the United States between April 2009 and Jan. 16, 2010. During that period, up to 378,000 people were hospitalized due to complications from H1N1 and 17,160 deaths occurred.

As always, the best protection against the flu is immunization, Koller said. Fortunately, this year's vaccine has been a good match to the viral strain circulating in the U.S. So getting a vaccine this late in the season can still offer protection.

"Now is a good time to get vaccinated because it takes about two weeks to develop an antibody response after the flu shot," Koller said.

Also, it's a good idea to continue to practice good personal hygiene such as covering your mouth when you cough and covering your nose when you sneeze and it's really important to wash your hands, Koller said.

"Flu is primarily spread by respiratory droplets," Koller said. "When somebody with influenza coughs or sneezes, out shoots this spray of flu virus that can infect anyone nearby."

SOURCE Loyola University Chicago Stritch School of Medicine