Influenza vaccine

Influenza vaccine

A flu shot being given to a US Navy crew member
Vaccine description
Target	Influenza virus
Vaccine type	inactivated, attenuated, recombinant
Clinical data
Trade names	Afluria, Fluarix, Fluzone, others
AHFS/Drugs.com	Inactivated: Monograph Intranasal: Monograph Recombinant: Monograph
Pregnancy category	AU: B1or B2 (depending on vaccine brand)[1][2][3]
Routes of administration	Intramuscular, intranasal, intradermal
ATC code	J07BB01 (WHO) J07BB02 (WHO), J07BB03 (WHO), J07BB04 (WHO)
Legal status
Legal status	AU: S4 (Prescription only)[1][2][4][5][6] CA: ℞-only / Schedule D[7][8][9][10][11] UK: POM (Prescription only) US: ℞-only[12][13][14][15][16][17][18][19][20][21][22][23] EU: Rx-only[24][25][26][27] In general: ℞ (Prescription only)
Identifiers
CAS Number	1704512-59-3
ChemSpider	none
KEGG	D04536

Influenza vaccines, colloquially known as flu shots^[28] or the flu jab,^[29] are vaccines that protect against infection by influenza viruses.^[30][31] New versions of the vaccines are developed twice a year, as the influenza virus rapidly changes.^[30] While their effectiveness varies from year to year, most provide modest to high protection against influenza.^[30][32] Vaccination against influenza began in the 1930s, with large-scale availability in the United States beginning in 1945.^[33][34]

Both the World Health Organization and the US Centers for Disease Control and Prevention (CDC) recommend yearly vaccination for nearly all people over the age of six months, especially those at high risk,^{[30][35][36][37]} and the influenza vaccine is on the World Health Organization's List of Essential Medicines.^[38] The European Centre for Disease Prevention and Control (ECDC) also recommends yearly vaccination of high-risk groups,^[39] particularly pregnant women, the elderly, children between six months and five years, and those with certain health problems.^[30][37]

The vaccines are generally safe, including for people who have severe egg allergies.^[40] A common side effect is soreness near the site of injection. Fever occurs in five to ten percent of children vaccinated, and temporary muscle pains or feelings of tiredness may occur. In certain years, the vaccine was linked to an increase in Guillain–Barré syndrome among older people at a rate of about one case per million doses.^[30] Influenza vaccines are not recommended in those who have had a severe allergy to previous versions of the vaccine itself.^[30][40] The vaccine comes in inactive and weakened viral forms. The live, weakened vaccine is generally not recommended in pregnant women, children less than two years old, adults older than 50, or people with a weakened immune system.^[30] Depending on the type it can be injected into a muscle (intramuscular), sprayed into the nose (intranasal), or injected into the middle layer of the skin (intradermal).^[30] The intradermal vaccine was not available during the 2018–2019 and 2019–2020 influenza seasons.^[41][42][43]