Symptoms of seasonal influenza include:

• sudden fever of 38.0°C (100.4°F) or higher
• dry cough
• aching body, especially head, lower back and legs
• extreme weakness and tiredness

Other symptoms can include:

• chills
• aching behind the eyes
• loss of appetite
• sore throat
• runny or stuffy nose

For people older than 75 with seasonal influenza, the temperature may be lower, for example 37.2°C (99.0°F). They may also experience vomiting, diarrhea or stomach pain.

Fever usually goes down and the person starts to feel better in 3 to 5 days. Tiredness and cough can continue for several weeks.

Seasonal influenza symptoms are different from those of a cold or gastroenteritis ("stomach flu").

Because the seasonal influenza virus is always changing, a new vaccine is created each year containing the three virus strains most likely to circulate. It takes 2 weeks for the vaccine to become effective. Even after seasonal influenza arrives in the community, it is not too late to get immunized.

The vaccine cannot cause seasonal influenza because the virus in the vaccine is killed. The vaccine is 70 - 90% effective in young, healthy people and protection lasts about 6 months. The vaccine is less effective for people with weakened immune systems, but if they are immunized, the illness will be less severe if they do become infected.

Since vaccine strains are selected 6 to 9 months before the start of seasonal influenza season, there is a slight chance the circulating strain may change before the season actually starts. The vaccine will NOT protect against other respiratory illnesses.