Influenza vaccines-the flu shot or flu jab-protect against infection by influenza viruses. New versions of the vaccines are developed twice a year, as the influenza virus mutates rapidly. While the vaccines effectiveness varies from year to year, most provide modest to high protection against influenza. Vaccine effectiveness in those under two years old and those over 65 years old remains but it is believed that vaccinating children may protect those around them. 

The World Health Organization (WHO) recommends annual vaccination for nearly all people over the age of six months, especially those at high risk. These groups include pregnant women, the elderly, children between six months and five years of age, those with certain health problems, and those who work in healthcare.

• 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.

Australia uses inactivated vaccines.

The Australian Government recommends seasonal flu vaccination for everyone over the age of six months. The flu vaccine is free for the following people:

• children aged six months to five years
  people aged 65 years and over
• Aboriginal and Torres Strait Islander people aged six months and over
• pregnant women
• anyone over six months of age with medical conditions such as severe asthma, lung disease or heart disease, low immunity or diabetes that can lead to complications from influenza.