Flu is a respiratory infection that infects the respiratory tract, including nose, throat, and sometimes lungs. Flu is a highly contagious disease and can spread easily from person to person. Flu usually occurs during the cold months of the year. In the United States, flu season generally occurs between October and May, although it can occur at anytime of the year. Influenza, also known as the flu, occurs easily and spreads easily from person to person. People who are considered high risk for the flu are as follows: children under age six months, also children under age five years, or adults over 65, residents of long-term facility or nursing homes, people who have or suffer from chronic illnesses, or immune compromise, pregnant women, Native Americans, also highest risk of the influenza are people who have unhealthy immune system or lowered immune system.