Potential side effects after receiving the flu vaccine include local reactions such as soreness, redness or swelling at the injection site, or systemic reactions including low grade fevers, stiffness and muscle aches, according to the Centers for Disease Control and Prevention. Side effects are mild and short-lived in comparison to the symptoms of the actual influenza virus.
The traditional flu vaccine is developed every year to protect against what research indicates are three of the most common influenza strains for the upcoming season, explains the CDC. Flu vaccines work by stimulating the body to produce antibodies against the injected strains approximately two weeks after receiving the vaccine. These antibodies then provide continued protection against those strains for the remainder of the season.
Flu vaccines are manufactured with either viruses that have been inactivated or without any viruses, states the CDC. Therefore, it isn’t possible to contract the flu virus from the vaccine, and any side effects or illnesses experienced following administration of the flu vaccine are coincidental. The flu vaccine is also available as a nasal spray, approved for anyone between the ages of 2 and 49. This form of vaccine is manufactured using an attenuated form of the flu virus. Side effects from the nasal spray include runny nose and a headache in children and adults, plus vomiting and wheezing in children and a cough in adults.