Other
Several studies have identified an increased incidence of narcolepsy among recipients of the pandemic H1N1 influenza AS03-adjuvanted vaccine; efforts to identify a mechanism for this suggest that narcolepsy is autoimmune, and that the AS03-adjuvanted H1N1 vaccine may mimic hypocretin, serving as a trigger.Some injection-based flu vaccines intended for adults in the United States contain thiomersal (also known as thimerosal), a mercury-based preservative. Despite some controversy in the media, the World Health Organizations Global Advisory Committee on Vaccine Safety has concluded that there is no evidence of toxicity from thiomersal in vaccines and no reason on grounds of safety to change to more-expensive single-dose administration. Types
Flu vaccines are available either as:
a trivalent or quadrivalent intramuscular injection (IIV3, IIV4, or RIV4, that is, TIV or QIV), which contains the inactivated form of the virus
a nasal spray of live attenuated influenza vaccine (LAIV, Q/LAIV), which contains the live but attenuated (weakened) form of the virus.TIV or QIV induce protection after injection (typically intramuscular, though subcutaneous and intradermal routes can also be protective) based on an immune response to the antigens present on the inactivated virus, while cold-adapted LAIV works by establishing infection in the nasal passages.
Flu vaccines are contraindicated for people who have experienced a severe allergic reaction in response to a flu vaccine or to any component of the vaccine. LAIVs are not given to children or adolescents with severe immunodeficiency or to those who are using salicylate treatments because of the risk of developing Reye syndrome. LAIVs are also not recommended for children under the age of 2, pregnant women, and adults with immunosuppression. Inactivated flu vaccines cannot cause influenza and are regarded as safe during pregnancy.While side effects of the flu vaccine may occur, they are usually minor, including soreness, redness, and swelling around the point of injection, headache, fever, nausea or fatigue. Side effects of a nasal spray vaccine may include runny nose, wheezing, sore throat, cough, or vomiting.In some people, a flu vaccine may cause serious side effects, including an allergic reaction, but this is rare. Furthermore, the common side effects and risks are mild and temporary when compared to the risks and severe health effects of the annual influenza epidemic. Guillain–Barré syndrome
Although Guillain–Barré syndrome had been feared as a complication of vaccination, the CDC states that most studies on modern influenza vaccines have seen no link with Guillain–Barré.