According to the CDC, the 2007 - 2008 flu season was the worst in 4 years. The last time we saw a flu season this bad was in 2003 - 2004. The data was based on adult and pediatric deaths from the flu and secondary infections, such as pneumonia. Although more deaths occurred in the 03 - 04 flu season, the number of weeks that we were above the epidemic level for flu has been longer this season. We recorded 13 weeks above the epidemic level this flu season, compared to 9 weeks in the 03 - 04 season.

• Learn More About the 07 - 08 Flu Season

The main reason this flu season was so bad was the ineffectiveness of the vaccine against the circulating strands of flu. The two main strands of flu that were causing illnesses this season were not including in the vaccine. However, the vaccine was still about 58 percent effective against the most common strain. So even though many people who got the flu shot still got the flu, they may have had some protection and likely did not get as sick as they would have otherwise.

• What You Need to Know About Flu Shots

Deciding which strains of flu to include in the vaccine each year is difficult and has to be an educated guess. Most of the time researchers get it right and the vaccine is between 70 and 90 percent effective. But other times the flu strains mutate in ways the researchers did not predict and we have a flu season like this one. While it is frustrating to get the flu, especially if got a flu shot, this is not a reason to believethat flu shots will not work in the future. They are still your best protection against the flu and usually do a very good job preventing the flu. This year was just an unfortunate exception.

• Did You Get the Flu After a Flu Shot?