Mild cases of influenza may resemble the common cold. Colds on the other hand never exhibit the severe symptoms and signs that may accompany influenza. The incubation of influenza is between 1 to 2 days. A person is infectious for about six days, including the day before onset of symptoms. Why winter is the predominant influenza season is not clear, but may be related to ease of transmission with people congregating indoors more during the winter.
Influenza vaccine is made from inactivated influenza virus particles.
The vaccine protects against certain strains of influenza. Since the strains of influenza which circulate change every year, it is necessary to make a new influenza vaccine for each season. This is why a yearly flu shot is recommended. May. Vaccination is still useful later in the season as it can help minimize the severity and protect against other influenza strains. It is possible to become infected after vaccination, particularly, for older adults whose immune systems may be less effective in responding to the vaccine.