Each year, it is predicted which strains of influenza will cause the most illness and these viruses are included in the vaccine. However, since viruses are continually changing due to mutations in viral genes, new strains not covered by the vaccine may be circulated . When the circulating virus is different than the vaccine strain, vaccination is still likely to reduce the severity of illness and the likelihood of complicatons. Compromised immune system. Again however, vaccination is still likely to reduce the severity of illness and the likelihood of complicatons.
Many people believe that the shot can actually cause the flu.
This is impossible because the viruses included in the vaccine are attenuated , or 'killed' viruses. They have been genetically altered so they are unable to cause the disease. The body still uses the attenuated virus as a kind of a blueprint to make antibodies, which can fight the live virus if ever confronted. The flu shot has a lot of side effects. While the vaccine, like any other medicine or vaccine, is capable of causing serious problems, the risk of it causing serious harm is extremely small.