What are the differences between the H1N1 flu and seasonal flu?

Both of these illnesses are caused by a strain of the influenza virus. While the strains that make up the season flu vary from year to year, the H1N1 virus represents a new strain that has never before circulated among humans. One big way the viruses differ is that the seasonal flu is primarily only a respiratory virus, meaning that it only affects breathing and your lungs, while the H1N1 affects the respiratory system and may also cause vomiting and nausea.
Both types of the flu are passed from person to person through droplets spread by coughing or sneezing or touching contaminated surfaces. The H1N1 flu can be spread in both warm weather and cold weather, unlike the seasonal flu which peaks during late December through early March and is most easily spread in cold weather.
The H1N1 virus is no more contagious than the season flu, but it does appear to be spreading faster among young people than among older people, according to the World Health Organization. While the majority of hospitalizations from the seasonal flu occur in seniors, most of the hospitalizations and deaths from H1N1 occur in people between the ages of 5 and 64 years, according to the Centers for Disease Control and Prevention (CDC).

There are several differences between the H1N1 flu and seasonal flu. H1N1, or swine flu, is most likely to afflict people under age 25, while seasonal flu occurs most often in people 65 and older. Both types of flu cause similar symptoms, including fever, coughing, sore throat, runny or stuffy nose, headaches, body aches, chills and fatigue. In addition, the H1N1 virus may cause vomiting and diarrhea.