SARS-CoV-2

• Although most cases are relatively mild, flu can cause more severe illness in young children and older people.
• Influenza virtually disappeared from Australia during the first years of the COVID-19 pandemic when public health restrictions reduced contact between people.
• Since 2022, it has returned to a seasonal pattern, although the flu season has started and peaked a few months earlier than before 2020.

What goes into a flu vaccine?

• Influenza strains are constantly changing due to genetic mutation, with the pace of genetic change much higher than for SARS-CoV-2 (the virus that causes COVID).
• Read more:
  Flu vaccine won't definitely stop you from getting the flu, but it's more important than you think

  All current influenza vaccines in Australia contain four different strains (known as quadrivalent vaccines).

What’s different about new flu vaccines?

• These include egg-based vaccines (Vaxigrip Tetra, Fluarix Tetra, Afluria Quad, FluQuadri and Influvac Tetra), cell-based vaccines (Flucelvax Quad), adjuvanted vaccines (Fluad Quad) and high-dose vaccines (Fluzone High-Dose Quad).
• Until recently, the process of manufacturing flu vaccines has remained similar.

• In some flu vaccines, adjuvants (components that stimulate the immune system) are included with the influenza antigens.
• For example, an adjuvant is used in the Fluad Quad vaccine, recommended for over 65s.
• Studies suggest adjuvanted influenza vaccines are slightly better than standard egg-based vaccines without adjuvant in older people.
• Read more:
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What should I do this year?

• Influenza vaccines are also recommended in pregnancy to protect both the mother and the baby for the first months of life.
• Influenza vaccines are widely available, including at GP clinics and pharmacies, while many workplaces have occupational programs.

In older people, a number of vaccines are now recommended: COVID and influenza, as well as one-off courses of pneumococcal and shingles vaccines. In general, most vaccines can be given in the same visit, but talk to your doctor about which ones you need.

Are there side effects?

• These are expected and reflect the immune system reacting appropriately to the vaccine, and are mostly mild and short-term.
• People with egg allergies should discuss this with their doctor, but in general, studies suggest they can safely receive any (including egg-based) influenza vaccines.
• Serious side effects from the influenza vaccine, such as Guillain-Barré syndrome, a neurological complication, are very rare (one case per million people vaccinated).

Allen Cheng receives funding from the National Health and Medical Research Council and the Australian Department of Health and Aged Care. He is a member of the Australian Technical Advisory Group on Immunisation.