Some physicians are predicting a rough flu season this year. With infections hitting their peak between December and February, public health officials recommend getting a flu shot as soon as possible. It can take up to two weeks for the vaccine from a flu shot to build immunity to the flu. According to the Centers for Disease Control and Prevention, because the effectiveness of different flu shots vary, discussing options with a personal doctor is a good idea. The CDC also recommends yearly flu shots for everyone over the age of six months. Last year, between 37 million and 43 million people got the flu. Deaths from the virus likely ranged between 36,400 and 61,200.