( CNN ) -- Flu vaccine myths can confuse people trying to decide whether to get a shot . Here are five common myths and , based on information from the Centers for Disease Control and Prevention , the truth . 1 . The shot can give you flu . Not so , says the CDC . The viruses in flu shots are killed during the production of the vaccine , which means they can not cause infection . The vaccine batches are then tested , with a group of people randomly assigned to get either the vaccine or salt water . `` The only differences in symptoms was increased soreness in the arm and redness at the injection site among people who got the flu shot , '' the CDC found . `` There were no differences in terms of body aches , fever , cough , runny nose or sore throat . '' Still , some people feel bad after a flu shot . Soreness at the injection site is one reason , but it usually dissipates within two days . It 's caused by the immune system making antibodies to the killed viruses in the vaccine that help a person fight off the flu . The Advisory Committee on Immunization Practices says symptoms , in rare instances , include fever , muscle pain , and discomfort or weakness , which also typically go away after a day or two . And , though a flu shot wo n't give you the flu , its protection does n't kick in for two weeks from the time of injection . During that time , you are vulnerable . In addition , it 's easy to confuse seasonal flu for an illness caused by a number of other pathogens , including rhinovirus . Or you may be exposed to a flu virus that is not included in the vaccine . Finally , the flu shot does not always work -- particularly among the elderly and people with weak immune systems . But even among these high-risk groups , the vaccine can prevent complications . 2 . It is better to get the vaccine later in the season to limit the risk that its efficacy will wane . No . The shot lasts an entire flu season , except for some children who may need two doses . The CDC recommends that all people older than 6 months get a flu vaccine . 3 . The flu shot might adversely affect my pregnancy . No . The flu vaccine is `` an essential element of prenatal care '' and is recommended for all pregnant women , according to the American College of Obstetricians and Gynecologists . Pregnant women are among the groups at increased risk for flu complications like pneumonia , infections and dehydration . Though babies can not be vaccinated until they have reached 6 months of age , antibodies they received in utero from their mothers may help protect them . But note that the group recommends against the nasal spray -- the live , attenuated version -- for pregnant women . The CDC says seasonal flu vaccine shots have not been shown to cause harm to pregnant women or their babies . 4 . I 've had the flu before and it was no big deal , so bring it on . No . Seasonal flu exacts a bigger toll in some years than in others : Between 1976 and 2007 , the flu was linked to a low of 3,000 to as many as 49,000 fatalities in the United States , with more than 200,000 hospitalizations . There are two main reasons : The viruses that circulate in one year may differ from those that circulate in another . And , of course , people change from year to year , meaning that your response to a viral infection one year may not be the same as your response in another . 5 . The flu shot does n't work . It does n't work all the time , but it does confer some level of protection . For example , the CDC says preliminary data for the 2010-2011 season show that it was about 60 % effective for all age groups combined , and studies for earlier years found protection rates of up to 90 % .
The flu vaccine can not give you the flu , according to the CDC . The shot lasts for an entire season , except for some kids who may need two . The vaccine is essential for pregnant women to protect their infants .