New flu vaccines will be offered in Australia in 2024. Here’s what you need to know about it | Allen Cheng

Influenza is a common respiratory infection. Although most cases are relatively mild, flu can cause more serious illness in young children and the elderly.

Flu pretty much disappeared from Australia during the early years of the Covid-19 pandemic, when public health restrictions reduced contact between people. Since 2022, the seasonal pattern has returned, although the flu season started and peaked a few months earlier than before 2020.

It is difficult to predict the intensity of the flu season at this time of year, but we can sometimes get clues from the Northern Hemisphere. Over there, the season started earlier than normal for the third year in a row (peak in early January instead of late February or March), with a similar number of reported cases and hospitalizations as the year before.

Flu vaccines are recommended annually, but there are now more and more different vaccine types. Here’s what you need to know about this year’s available shots from this month.

What is in a flu vaccine?

Like other vaccines, flu vaccines work by ‘training’ the immune system on a harmless component of the flu virus (known as an antigen) so that it can respond appropriately when the body comes into contact with the real virus.

Influenza strains are constantly changing due to genetic mutation, at the rate of genetic mutations change much higher than for Sars-CoV-2 (the virus that causes Covid). The strains used in the vaccine are reviewed twice a year by the World Health Organization, which selects vaccine strains that match the predicted circulating strains of the following season.

All current flu vaccines in Australia contain four different strains (known as quadrivalent vaccines). One of the tribes appeared to disappear during the Covid pandemic, and the The WHO recently recommended this removing this strain from the vaccine. It is expected that trivalent vaccines (three strains) will become available in the near future.

What’s different about new flu vaccines?

There are eight brands of flu vaccines available in Australia in 2024. 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 production process of flu vaccines remained similar. Since the development of the flu vaccine in the 1940sInfluenza viruses were grown in chicken eggs and then extracted, inactivated, purified and processed to form the egg-based vaccines that are still widely used today.

However, several improvements have been made to flu vaccines in recent years.

The immune system of the elderly generally does not respond as strongly to vaccines. In some flu vaccines, adjuvants (components that stimulate the immune system) are included with the flu antigens. For example, an adjuvant is used in the Fluad Quad vaccine, recommended for people over 65. Studies suggest that adjuvanted flu vaccines are slightly better than standard egg-based vaccines without adjuvant in the elderly.

An alternative approach to improving the immune response is to use higher doses of the vaccine strains. An example is Fluzone High-Dose Quad – another option for older adults – which contains the equivalent of four doses of a standard flu vaccine. Research shows that the high-dose vaccine is better than the standard-dose vaccine (without adjuvant) in preventing hospital admissions and complications in the elderly.

Other manufacturers have updated the production process. Cell-based vaccines, such as Flucelvax Quad, use cells instead of eggs in the manufacturing process. Other vaccines do not yet available also use different technologies. In the past, production problems with egg-based vaccines have reduced their effectiveness. The use of an alternative production method offers some certainty against this in the future.

What should I do this year?

Given indications that flu season may happen earlier than normal this year, it’s probably safest to get your vaccine early. This is especially important for people at highest risk of serious illness, including older adults (65 years and over), people with chronic medical conditions, young children (six months to five years) and Aboriginal and Torres Strait Islander people. Flu vaccines are also recommended during pregnancy to protect both mother and baby during the first months of life.

Flu vaccines are widely available, including from GP clinics and pharmacies, while many workplaces have vocational programs in place. For risk groups four of the vaccines are subsidized by the Australian government through the National Vaccination Program.

There are a number of vaccines available for older people now recommended: Covid and flu, as well one-off courses of pneumococcal therapy And shingles vaccines. Generally, most vaccines can be given during the same visit, but talk to your doctor about which vaccines you need.

Are there any side effects?

All flu vaccines can cause a sore arm and sometimes more general symptoms such as fever and fatigue. These are expected and reflect the immune system responding appropriately to the vaccine, and are usually mild and short-lived. These side effects are slightly more common with adjuvanted vaccines and high-dose vaccines.

As with all medications and vaccines, allergic reactions such as anaphylaxis may occur after the flu vaccine. All vaccine providers are trained to recognize and respond to anaphylaxis. People with an egg allergy should discuss this with their doctor, but in general: studies suggest they can safely receive all flu vaccines (including egg-based ones).

Serious side effects from the flu vaccine, such as Guillain-Barré syndrome, a neurological complication, are very rare (one case per million vaccinated people). They are thought to occur less often after influenza vaccination than after influenza infection.

Allen Cheng is professor of infectious diseases at Monash University. This article was originally published in the conversation

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