What is it?

Influenza viruses are single stranded RNA orthomyxoviruses which can cause acute viral infections of the respiratory tract. Infections are often classified according to the type of influenza virus responsible for the infection, typically A, B, or C, with influenza types A and B more commonly responsible for causing severe disease. Influenza A can be further subtyped based on the differences in their surface antigens.

What to look for

The incubation period of influenza disease is 1-4 days with typical symptoms including fever, headache, myalgia (muscle aches), lethargy (tiredness), coryza (runny nose), sore throat and cough. Gastrointestinal symptoms such as nausea, vomiting and diarrhoea can also occur. Children with influenza will often present with symptoms of croup.

Most influenza infections will resolve within 2-7 days, however complications including otitis media (ear infections), secondary bacterial pneumonia (lung infections) and encephalitis (brain inflammation), can prolong the illness and disease outcomes.

How is it transmitted

Influenza is highly contagious. Transmission is via respiratory droplets, aerosol or through direct contact with the respiratory secretions of an infected person.

Epidemiology

Influenza disease can occur as sporadic cases, as an epidemic, or as a pandemic. Whilst outbreaks more commonly occur in the winter months in temperate climates, there is a greater variation seen in the timing of cases in the tropics.

Aged care facilities, health care facilities and child care centres are well recognised as high-risk areas for influenza outbreaks.

Pregnant women, children < 5 years of age, those aged > 65 years, people with underlying medical conditions, and Aboriginal and Torres Strait Islander peoples carry the highest rates of morbidity and mortality within Australia.

Prevention

Influenza vaccination is available and recommended for anyone ≥ 6 months of age who wish to be protected against influenza disease and its complications. Due to the circulating strains of influenza virus changing each year, vaccination is recommended annually to provide the most effective protection against disease.

Influenza vaccines are provided for free on the National Immunisation Program (NIP) for high-risk groups, including:

Those aged 6 months of age and over who do not qualify for funded vaccines can purchase vaccines privately through some councils, GPs and pharmacies.

Vaccine platform

The influenza vaccines available in Australia are inactivated, meaning that they cannot replicate and cause influenza disease. They can be cell-based or egg-based depending on how they are manufactured.

Traditional influenza vaccines are made by cultivating influenza viruses in chicken eggs. Cell-based influenza vaccines are made by growing influenza viruses in animal cells lines (canine kidney). By using a cell-based platform, influenza vaccines have the potential to provide protection against influenza strains that are more closely matched to the circulating influenza strains in the community.

Cell-based influenza vaccines have been used internationally since 2012 and in 2021 a cell-based influenza was registered for use within Australia for the first time. Flucelvax quad® is available for private purchase for immunisation of those aged ≥ 2 years.

In 2023 the influenza virus strains included in the seasonal influenza vaccines are the same for both cell-based and egg-based vaccines:

  • A/Sydney/5/2021 (H1N1) pdm09-like virus
  • A/Darwin/9/2021 (H3N2)-like virus
  • B/Austria/1359417/2019-like (B/Victoria lineage)-like virus
  • B/Phuket/3073/2013-like (B/Yamagata lineage)-like virus

Adjuvanted vaccines

Due to a gradual decline in effectiveness of the immune system of older people (a process known as immunosenescence) immunity following vaccination with standard influenza vaccines can be suboptimal. In addition, those aged ≥ 65 years have the highest rates of influenza disease burden and associated complications including pneumonia and death. It is for this reason that adjuvanted influenza vaccines are the preferred vaccine type for the older population.

There are two adjuvanted influenza vaccines registered for use in Australia:

  • Fluad® Quad- registered for use in adults ≥ 65 years and funded under the NIP
  • Fluzone High-Dose Quad- registered for use in individuals aged ≥ 60 years and privately available on prescription.

Table 1: The 2023 influenza vaccine brand recommendations according to age

* 2 doses, minimum of 4-weeks apart should be given to children < 9 years of age in the first year of receiving the influenza vaccine, a single dose is recommended in subsequent years.
#Adjuvanted quadrivalent influenza vaccines are preferentially recommended for people adults ≥ 65 years.
βFluarix-tetra®/FluQuadri®/Afluria Quad®/Vaxigrip tetra®/Influvac tetra®/ Flucelvax Quad® are registered for use in those aged ≥ 65 years however adjuvanted vaccines are the preferred vaccines for this age group.
^2 doses are recommended in the first year following SOT/HSCT regardless of history of influenza vaccination due to immunosuppression. The exception to this is in individuals receiving an adjuvanted influenza vaccine where only 1 dose is recommended.
shaded boxes indicate vaccines funded under the NIP for eligible individuals.
shaded boxes not registered for use in this age group.
shaded boxes indicate adjuvanted vaccines.

Expected side effects

Common side effects following vaccination include pain, redness and swelling at the injection site as well as fever, malaise and myalgia. Symptoms usually occur within the first 24-48 hours following immunisation.

Cell-based influenza vaccines have a similar side-effect profile to traditional egg-based influenza vaccines. Side effects may occur slightly more commonly following immunisation with adjuvanted quadrivalent formulations than with standard influenza vaccine formulations.

Commonly asked questions

  • When is the ideal time to be immunised against the flu?

    Annual vaccination before the onset of influenza season is recommended for all individuals ≥ 6 months of age. The peak period of circulating influenza disease in Australia is typically June to September, however out of season cases can and do occur. Optimal protection against influenza occurs within the first 3-4 months following vaccination. It is never too late in the season to vaccinate.

    Pregnant women can safely receive the influenza vaccine during any stage of pregnancy. Where a pregnancy crosses over seasons, some pregnant women may be recommended to receive 2 influenza vaccines, one from each year.

  • Do healthy people need to be immunised against influenza?

    Influenza can be a very serious disease resulting in hospitalisation and death. Even in cases where disease and its complications are not severe, it can cause a great inconvenience for the individual, including the cost of GP visits and medications, as well as time off work for themselves or to care for their sick child.

    In some cases, a person may not get severe disease however infection can be spread to other people. This can be significant when it is spread to those who are too young to be immunised or are at higher risk of complications of disease.

  • If an individual has had confirmed influenza disease this year, are they still recommended to receive an influenza vaccine and when should they receive it?

    The influenza vaccine would still be recommended for someone with a history of confirmed influenza infection as the vaccine protects against multiple strains of influenza disease. The influenza vaccine can be administered as soon as the patient has recovered from their illness.

  • Can the influenza vaccine be given at the same time as other vaccines?

    Generally speaking, yes, influenza vaccines may be co-administered with most other vaccines on the same day. This includes live-attenuated vaccines (eg. measles and varicella) and the pertussis vaccine in pregnancy.

    COVID-19 vaccines can safely be co-administered with influenza vaccines however in children aged 6 months – 5 years of age an interval of 7-14 days is preferred to minimise adverse events such as fever.

    Whilst co-administration of Fluad®Quad and Shingrix is acceptable, there is limited safety data on this and therefore it is preferred to separate their administration by several days.

  • If a patient received a 2022 influenza vaccine at the end of the season in early 2023, do they still need a 2023 influenza vaccine?

    Yes. A 2023 influenza vaccine is still recommended in order to provide protection against this year’s circulating strains. A minimum interval of 4 weeks is recommended.

  • In children < 9 years of age who received the influenza vaccine for the first time last year but only received 1 dose, how many doses are required this year?

    Only 1 dose is required in this instance. 2 doses of the influenza vaccine are recommended for children < 9 years of age in the first year of receiving the vaccine, however if the second dose was inadvertently missed, it does not require catch up and only 1 dose is required in future years.

  • Are influenza vaccines safe for people with allergies?

    Based on prospective and retrospective studies of influenza vaccination in those with and without egg allergy (including egg anaphylaxis), the presence of egg allergy does not increase the risk of allergic reactions to the influenza vaccine. Egg-based influenza vaccines can be administered in community vaccination clinics (which may or may not have direct medical practitioner supervision), General Practitioner surgeries or immunisation clinics, as a single dose followed by the recommended 15 minute observation period. It is not necessary to preferentially administer cell-based influenza vaccines in this patient group.

    All influenza vaccines available under the NIP in 2023 are latex free meaning that people with a latex allergy can safely be vaccinated.

For further queries on influenza vaccination, please contact us via our immunisation support.

Resources

Authors: A/Prof Nigel Crawford (Director SAEFVIC, Murdoch Children’s Research Institute), Rachael McGuire (Research Nurse SAEFVIC, Murdoch Children’s Research Institute), Georgina Lewis (Clinical Manager SAEFVIC, Murdoch Children’s Research Institute) and Mel Addison (Research Nurse SAEFVIC, Murdoch Children’s Research Institute).

Reviewed by: Rachael McGuire (MVEC Education Nurse Coordinator).

Date: March 21, 2023

Materials in this section are updated as new information becomes available. The Melbourne Vaccine Education Centre (MVEC) staff regularly review materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family’s personal health. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult a healthcare professional.