COVID-19 vaccine booster doses

As new strains of the COVID-19 virus emerge, booster doses can protect you from severe illness and hospitalisation. Find out more about booster doses for COVID-19 vaccines.

What is a booster dose?

A booster dose is an extra dose of a vaccine after the primary course of two doses has been given.1

Booster doses are common for some vaccines given as part of the National Immunisation Program (NIP) Schedule, such as diphtheria, tetanus and pertussis (whooping cough).2

Table 1: Primary COVID-19 vaccine course definitions in Australiaa,1

General population

Two doses of the following approved COVID-19 vaccines available in Australia:

  • COMIRNATY (tozinameran) – Pfizer Australia
  • SPIKEVAX (elasomeran) – Moderna Australia
  • VAXZEVRIA – AstraZeneca
  • NUVAXOVID (NVX-CoV2373) – Biocelect on behalf of Novavax

OR

One dose of the following COVID-19 vaccine, which is registered but not available in Australia:

  • COVID-19 Vaccine Janssen – Janssen-Cilag

People who are severely immunocompromised

Three doses of an approved COVID-19 vaccine, as recommended by the Australian Technical Advisory Group on Immunisation (ATAGI)

aThe definition of an acceptable primary course includes mixed schedules of these vaccines, as well as TGA-recognised vaccines

Find out more about vaccines and COVID-19.

In Australia, there are three vaccines with provisional approval for use as a booster dose:3

  • COMIRNATY (tozinameran) – Pfizer Australia (for people aged 12 years and older)
  • SPIKEVAX (elasomeran) – Moderna Australia (for people aged 18 years and older)
  • VAXZEVRIA – AstraZeneca (for people aged 18 years and older)

The Australian Technical Advisory Group on Immunisation (ATAGI) recommends booster doses for all Australians aged 16 years or older. This will help keep immunity to the virus at high levels1 and help keep people protected as new strains of the COVID-19 virus emerge.

ATAGI has reviewed evidence on the benefits and risks of a booster dose of Pfizer COVID-19 vaccine in adolescents in Australia aged 12-15 years. Current data suggest that COVID-related serious illness is very rare in adolescents aged 12-15, particularly after completion of a primary series of COVID-19 vaccination.4

At this time, ATAGI does not recommend that adolescents aged 12-15 years need to receive a booster dose of Pfizer COVID-19 vaccine and will continue to review international evidence on efficacy of a booster in this age group.4

The messenger RNA (mRNA) vaccines (Pfizer or Moderna) are the ATAGI preferred vaccines for booster doses, noting the Pfizer COVID-19 vaccine is the only registered vaccine for use in people aged 16 to 17 years. It doesn't matter which vaccine you got for your primary course.1,5 The mRNA vaccines appear to work better as a booster dose compared with other COVID-19 vaccines. A study has shown they give the highest boost in antibodies compared with AstraZeneca, when given as a booster dose.1,6

VAXZEVRIA (AstraZeneca) can be given as a booster dose if someone is unable to receive one of the mRNA vaccines. The only scenario in which ATAGI actively recommends a booster dose using AstraZeneca is for people who can’t receive an mRNA vaccine, for example people with allergic reactions or myocarditis.1 Myocarditis is a disease that causes the heart muscle to become inflamed.7 Myocarditis and pericarditis are known reactions in a small number of people who receive mRNA COVID-19 vaccines.1

Information about the safety and immune response of NUVAXOVID (Novavax) as a booster dose is limited. Although not registered for this use, it can be given as a booster dose for people aged 18 years and older if no other COVID-19 vaccine is suitable.1

Find out more about booster doses for COVID-19 vaccines from the Australian Government Department of Health.

Staying up to date

It is important to stay up to date with your COVID-19 vaccination. Booster doses are not mandatory but are highly recommended to ensure you have the highest protection you can get. Your digital vaccination certificate is updated when you receive each dose of vaccine. This includes your booster dose.8

If you are 16 years of age or older, an up to date COVID-19 vaccination status requires:9

  • completing a primary course, and
  • getting a booster dose at least 3 months after the primary course, and before 6 months.

If you didn’t get a COVID-19 vaccine booster dose before 6 months, it is still safe and effective to get it at any time after 6 months. This will make you up to date.9 You should get the booster dose in the advised timeframe for your age or health status. If not, your status is overdue.8

What is the difference between a third dose and a booster dose?

ATAGI recommends a third dose of the COVID-19 vaccine as part of the primary course if you are aged 5 years or older and severely immunocompromised. This will help boost your immune response.10

A booster dose is an extra dose of a vaccine. You receive it after the primary course, as protection against infection decreases over time.1

You can still receive a booster dose after getting your third dose. If you are 16 years of age or older with severe immunocompromise, you should get the booster dose 3 months after the third primary dose. This is in line with the timing for the general population.1

 

Who can get a COVID-19 vaccine booster dose?

You can get a booster dose if you:1

  • are 16 years of age or older, and
  • have finished your primary vaccine course at least 3 months ago.

If you are severely immunocompromised, you can get a booster dose 3 months after you finish your 3-dose primary course.1

If you are pregnant, you can get a booster dose 3 months after you finish your primary course.1

Children aged under 16 years are not recommended to get a booster dose. Severe COVID-19 is not common in this age group. The primary course generates a strong immune response. Current evidence suggests the benefits from booster doses in children are likely to be small.11

You can get either the Pfizer or Moderna vaccine as a booster dose. It doesn’t matter which vaccine you received for your primary course.1,5 Studies have shown that mixing COVID-19 vaccines for the primary course is safe. It triggers a similar, or improved, immune response.12,13

 

Who can get a winter booster dose of COVID-19 vaccine?

ATAGI recommends an additional booster dose (winter booster dose) to increase vaccine protection before winter for people who are at the greatest risk of severe illness from COVID-19.14

You can get an winter booster dose if you have received your primary course and first booster and if you are:14

  • aged 65 years or older
  • a resident of an aged care or disability care facility
  • aged 16 years and older with severe immunocompromise, or
  • Aboriginal and/or Torres Strait Islander aged 50 years or older.

The additional booster dose can be given from 4 months or longer after you have received your first booster dose. If you have a confirmed COVID-19 infection after getting your first booster, you should get your additional booster dose from 4 months after the confirmed infection, as infection can boost immunity.14

 

Can I get a COVID-19 vaccine booster dose if I have COVID-19?

If you test positive for COVID-19, defer your booster dose until you have recovered from acute illness. 5,11 For most people, this is around 4–6 weeks after infection.15 You should not defer your booster dose by more than 4 months.5,11

You should get your winter booster dose (if eligible) from 4 months after a confirmed COVID-19 infection if the infection occurred after your first booster dose.14

 

What are the benefits of a booster dose?

People who receive a booster have lower rates of COVID-19 infection, as well as lower chances of hospitalisation, severe disease and death from a COVID-19 infection, compared with those in people who do not receive a booster dose.16-19

Booster doses also trigger improved immune responses20-22 and boosted immunity.6

Boosters are an important prevention option for most people over the age of 16 years and are especially helpful for:1,23

  • people at a greater risk of severe COVID-19 infection, including those:
    • aged ≥ 50 years
    • with underlying medical conditions
    • living in aged care facilities
    • Aboriginal and Torres Strait Islanders
  • people at high job-related risk of COVID-19, and
  • people living in areas where there is active spread.

The expected benefits of getting a booster dose at 3 months are:1

  • a low chance of illness with symptoms from COVID-19 caused by current strains
  • a low chance of severe illness from COVID-19 caused by current strains
  • a low chance of death from COVID-19 caused by current strains, and
  • lowered impacts on the healthcare system, combined with improved public health and social measures.
 

How long does protection against COVID-19 last after a booster dose?

Although COVID-19 vaccines work well,24 protection against COVID-19 wanes over time.25 A booster dose will help you strengthen your immunity against COVID-19. It will make sure the protection you get from the primary course is even stronger and longer lasting. It will also help prevent spread of the virus.5

The duration of protection from a booster dose is currently unclear. Studies have shown booster doses lower the risk of infection and the risk of decreasing immunity in the short term.26,27 Effectiveness against severe illness and hospitalisation decreases 4 months after a booster dose.28

 

Are booster doses safe?

Booster doses of mRNA vaccines are safe and well tolerated.20,21 Some people have unwanted effects after taking a medicine or vaccine. These are also called side effects or adverse events.

Side effects from booster vaccines are generally mild or moderate.29 The most common ones are feeling tired, headache, joint stiffness and muscle pain.20

A UK study has reviewed the safety of the AstraZeneca, Moderna and Pfizer vaccines as booster doses. When given at least 70 to 84 days after a primary course, there were no safety concerns for any of the vaccines.6

If someone experienced side effects, these were usually reported the day after the booster dose. The types of side effects were similar to those reported after the second dose of the primary course.30

There are limited data on serious side effects such as myocarditis and pericarditis following a booster dose of the Pfizer or Moderna vaccine. Myocarditis and pericarditis following vaccination with Pfizer are not more common after the booster dose, compared with the second dose. There is not enough data available yet to show the rates of myocarditis and pericarditis following a booster dose of Moderna.5

You can get your booster dose at the same time as other non-COVID-19 vaccines. This includes the flu vaccine.1,11

 

Can I still spread COVID-19?

You can still contract and spread COVID-19 even after a booster dose, but breakthrough (recurrent) infections are far less likely to be serious. It may make you less likely to spread breakthrough infections. This is due to lower amounts of the virus in your body (viral load) following a booster dose.27

Studies have shown the chance of you getting COVID-19 after completing a primary course is much lower than for unvaccinated people.31 Breakthrough infections in vaccinated people have lower viral loads than those in people who are unvaccinated. This effect starts to decline after 2 months. It vanishes 6 months or longer after vaccination. A booster dose restores this effect on reducing breakthrough infection viral loads.27

You should still get tested as soon as you can if you have cold or flu-like symptoms, even if they are mild.

Find out more about COVID-19 symptoms and how to get tested.

 

Will booster doses protect me from current and future strains of the COVID-19 virus?

We know from studies that booster doses are very good at protecting us against severe disease from current strains.20,22 This includes the Beta, Gamma and Delta strains.20 However, there is not enough evidence to determine their efficacy against future strains.

A booster dose of an mRNA vaccine following a primary course of two doses triggers a stronger immune response against the COVID-19 virus compared with two doses, including the Delta and Omicron strains.32,33

A booster dose with an mRNA vaccine is 80–95% effective against hospitalisation due to the Omicron strain for the first 3 months. It is 75–85% effective at 4–6 months. It is 85–99% effective against death due to the Omicron strain for the first 3 months.34

 

Will I need another COVID-19 vaccination after my booster dose?

An additional booster dose is recommended before winter for those who are at the greatest risk of severe illness from COVID-19.14 The additional winter booster dose can be given from 4 months or longer after an individual has received their first booster dose, or from 4 months after a confirmed COVID-19 infection if infection occurred since the individual’s first COVID-19 booster dose.14

As a result of emerging evidence, ATAGI may update its recommendations as required. It is not possible to pre-empt whether changes to the advice on winter doses will be made, nor broader recommendations for the COVID-19 Vaccination Program.

Not all vaccines give lifelong immunity. The influenza vaccine, for example, is usually given every year. Other vaccines, such as the polio vaccine, may also need booster doses to help keep you protected from infection.35

 
 

References

  1. Department of Health. ATAGI recommendations on the use of a booster dose of COVID-19 vaccine. Canberra: Australian Government Department of Health, 2022 (accessed 9 March 2022).
  2. Department of Health. National Immunisation Program Schedule. Canberra: Australian Government Department of Health, 2022 (accessed 23 March 2022).
  3. Therapeutic Goods Administration. COVID-19 vaccine: Provisional registrations. Canberra: Australian Government Department of Health, 2022 (accessed 9 March 2022).
  4. Department of Health. ATAGI statement on use of booster doses in adolescents aged 12-15 years. Canberra: Australian Government Department of Health, 2022 (accessed 27 April 2022).
  5. Department of Health. COVID-19 booster vaccine advice. Canberra: Australian Government Department of Health, 2022 (accessed 9 March 2022).
  6. Munro APS, Janani L, Cornelius V, et al. Safety and immunogenicity of seven COVID-19 vaccines as a third dose (booster) following two doses of ChAdOx1 nCov-19 or BNT162b2 in the UK (COV-BOOST): a blinded, multicentre, randomised, controlled, phase 2 trial. Lancet 2021;398:2258-76.
  7. Department of Health. Comirnaty (Pfizer), Spikevax (Moderna) and cardiac inflammation. Canberra: Australian Government Department of Health, 2022 (accessed 27 April 2022).
  8. Department of Health. Stay up to date with your COVID-19 vaccines. Canberra: Australian Government Department of Health, 2022 (accessed 9 March 2022).
  9. Department of Health. ATAGI statement on defining 'up-to-date' status for COVID-19 vaccination. Canberra: Australian Government Department of Health, 2022 (accessed 9 March 2022).
  10. Department of Health. Recommendations on the use of a 3rd primary dose of COVID-19 vaccine in individuals who are severely immunocompromised. Canberra: Australian Government Department of Health, 2022 (accessed 9 March 2022).
  11. Department of Health. Clinical recommendations for COVID-19 vaccines. Canberra: Australian Government Department of Health, 2022 (accessed 9 March 2022).
  12. Hillus D, Schwarz T, Tober-Lau P, et al. Safety, reactogenicity, and immunogenicity of homologous and heterologous prime-boost immunisation with ChAdOx1 nCoV-19 and BNT162b2: a prospective cohort study. Lancet Respir Med 2021;9:1255-65.
  13. Liu X, Shaw RH, Stuart ASV, et al. Safety and immunogenicity of heterologous versus homologous prime-boost schedules with an adenoviral vectored and mRNA COVID-19 vaccine (Com-COV): a single-blind, randomised, non-inferiority trial. Lancet 2021;398:856-69.
  14. Department of Health. ATAGI statement on recommendations on a winter booster dose of COVID-19 vaccine. Canberra: Australian Government Department of Health, 2022 (accessed 28 March 2022).
  15. NSW Health. Booster vaccination - frequently asked questions. St Leonards, NSW: NSW Government NSW Health, 2022 (accessed 27 April 2022).
  16. Barda N, Dagan N, Cohen C, et al. Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational study. Lancet 2021;398:2093-100.
  17. Arbel R, Hammerman A, Sergienko R, et al. BNT162b2 vaccine booster and mortality due to Covid-19. N Engl J Med 2021.
  18. Bar-On YM, Goldberg Y, Mandel M, et al. Protection against Covid-19 by BNT162b2 booster across age groups. N Engl J Med 2021.
  19. Bar-On YM, Goldberg Y, Mandel M, et al. Protection of BNT162b2 vaccine booster against Covid-19 in Israel. N Engl J Med 2021;385:1393-400.
  20. Choi A, Koch M, Wu K, et al. Safety and immunogenicity of SARS-CoV-2 variant mRNA vaccine boosters in healthy adults: an interim analysis. Nat Med 2021;27:2025-31.
  21. Flaxman A, Marchevsky NG, Jenkin D, et al. Reactogenicity and immunogenicity after a late second dose or a third dose of ChAdOx1 nCoV-19 in the UK: a substudy of two randomised controlled trials (COV001 and COV002). Lancet 2021;398:981-90.
  22. Eliakim-Raz N, Leibovici-Weisman Y, Stemmer A, et al. Antibody titers before and after a third dose of the SARS-CoV-2 BNT162b2 vaccine in adults aged >/=60 years. Jama 2021;326:2203-4.
  23. Department of Health. Clinical features of COVID-19 disease. Canberra: Australian Government Department of Health, 2022 (accessed 17 March 2022).
  24. Lopez Bernal J, Andrews N, Gower C, et al. Effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines on covid-19 related symptoms, hospital admissions, and mortality in older adults in England: test negative case-control study. BMJ 2021;373:n1088.
  25. Levin EG, Lustig Y, Cohen C, et al. Waning Immune Humoral Response to BNT162b2 Covid-19 Vaccine over 6 Months. N Engl J Med 2021.
  26. Patalon T, Gazit S, Pitzer VE, et al. Odds of testing positive for SARS-CoV-2 following receipt of 3 vs 2 doses of the BNT162b2 mRNA vaccine. JAMA Intern Med 2021.
  27. Levine-Tiefenbrun M, Yelin I, Alapi H, et al. Viral loads of Delta-variant SA