What is the difference between a pandemic and a seasonal outbreak of the flu?
A pandemic is caused by a new influenza virus that most people have not been exposed to, so there is little or no pre-existing immunity. Seasonal flu is a contagious respiratory illness caused by influenza viruses that are similar to previous years. Some people may have built up immunity and there also is a vaccine for each year’s flu season. It can cause mild to severe illness and is responsible for about 36,000 deaths each year in the United States, including about 1,800 deaths in Illinois.
