The goal of the Australian COVID-19 vaccination program remains the prevention of severe illness from COVID-19. ATAGI has evaluated this risk in the context of high population levels of hybrid immunity (i.e., combined immunity from past infection and past vaccination), the evidence regarding COVID-19 vaccine effectiveness, including for new bivalent vaccines, and the changing epidemiology of COVID-19 related to newly emerged subvariants of Omicron.
These recommendations replace previous ATAGI COVID-19 vaccine booster advice.
- ATAGI recommends a 2023 COVID-19 vaccine booster dose for adults in the following groups, if their last COVID-19 vaccine dose or confirmed infection (whichever is the most recent) was 6 months ago or longer, and regardless of the number of prior doses received:
- All adults aged 65 years and over
- Adults aged 18-64 years who have medical comorbidities that increase their risk of severe COVID-19, or disability with significant or complex health needs.
- ATAGI advises the following groups should consider a 2023 booster dose if their last COVID-19 vaccine dose or confirmed infection (whichever is the most recent) was 6 months ago or longer, and regardless of the number of prior doses received, based on an individual risk benefit assessment with their immunisation provider.
- All Adults aged 18-64 years without risk factors for severe COVID-19
- Children and adolescents aged 5-17 years who have medical comorbidities that increase their risk of severe COVID-19, or disability with significant or complex health needs.
- ATAGI advises that a booster dose is not recommended at this time for children and adolescents aged under the age of 18 who do not have any risk factors for severe COVID-19.
- Regarding vaccine choice, all currently available COVID-19 vaccines are anticipated to provide benefit as a booster dose, however bivalent mRNA booster vaccines are preferred over other vaccines. These include: Pfizer Original/Omicron BA.4/5, as well as Pfizer Original/Omicron BA.1 or Moderna Original/Omicron BA.1. Moderna Original/Omicron BA.4/5 is currently under evaluation by the Therapeutic Goods Administration.
- COVID-19 vaccine can be co-administered with influenza and other vaccines.
- Administration of a 2023 COVID-19 booster dose should aim to occur prior to June 2023 and at a time of 6 months or greater following the most recent COVID-19 vaccine dose or confirmed infection.
- Ongoing surveillance of COVID-19 infection rates and clinical outcomes, new variants, and vaccine effectiveness will inform future recommendations for additional booster doses.
No risk factors
≥ 65 years
Epidemiology of SARS-CoV-2 as of February 2023
Multiple new Omicron subvariants have emerged since the BA.4/5 wave in Australia during July and August 2022, displaying increased immune-escape properties (e.g. BQ.1 and XBB)1,2. These have co-circulated without any specific subvariant establishing clear dominance. Numerous immunological studies report reduced neutralisation of new Omicron subvariants by both vaccine-induced and naturally derived antibodies3,4. COVID-19 vaccines may have a reduced and/or shorter duration of protection against infection from these subvariants compared with older variants, however vaccines (together with hybrid immunity from natural infection) continue to provide strong protection against severe COVID-19. Of note, early evidence suggests that the newer Omicron subvariants do not cause more severe disease compared with the original Omicron subvariant (BA.1)5.
Anticipated benefits of a 2023 COVID-19 vaccine booster dose
An additional COVID-19 booster dose is anticipated to address waning of protection against severe COVID-19 prior to winter. This will provide an increase in protection against severe illness and protect the healthcare system during a time of high demand.
It is recommended to defer vaccination for 6 months following a confirmed SARS-CoV-2 infection, as this, together with prior vaccine doses received, will boost protection against COVID-19. ATAGI notes that testing rates have decreased and there are likely to have been many people with undetected SARS-CoV-2 infection within recent months. There are no safety concerns for individuals receiving a COVID-19 vaccine who may have had undetected SARS-CoV-2 infection within the past 6 months.
The increase in protection against severe illness from COVID-19 following a booster dose is most beneficial for people at higher risk of severe illness, i.e., older adults and those with relevant medical risk factors6,7. Studies conducted throughout the pandemic, including during Omicron epidemic waves have identified a higher risk of hospitalisation among older adults and adults with immunosuppression or other chronic medical conditions, compared with younger or healthy adults8,9.
ATAGI considers a booster dose beneficial for all adults aged 65 years and older. The risk of severe disease increases with each decade of age. With similar levels of hybrid immunity to the Australian population, UK modelling during the Omicron era found that 800 people aged 70 years and above would need to be given a booster to prevent one hospitalisation from COVID-19, compared with 8000 people aged 50 to 59 years and 92,500 people aged 40-49 years10. However, a booster dose may still be beneficial for people aged 5-64 years based on individual circumstances such as underlying conditions that increase their risk of severe disease.
For children and adolescents aged 5-17 years with risk factors for severe illness, a booster dose may be beneficial; decision-making around booster vaccination should be based on an individual risk-benefit assessment with their immunisation provider. The risk of severe disease with current high population levels of hybrid immunity in children and adolescents aged 5-17 years without risk factors is now considered to be lower than when previous ATAGI booster advice was issued. At present, most at-risk children aged 6 months to <5 years who have received a primary course have done so within recent months and a booster dose is not recommended at present.
ATAGI continues to recommend a primary course of vaccination against COVID-19, followed by a booster dose for those eligible, even in individuals who have had past infection. Adults who have already been infected with an Omicron subvariant and vaccinated with 3 doses of COVID-19 vaccine are at lower risk of reinfection and hospitalisation compared to those who have been infected but not vaccinated11.
Potential risks of a COVID-19 booster dose
For people aged under 65 years, the decision to have a 2023 COVID-19 booster dose in the coming months should take into account an individual’s age, risk factors for severe COVID-19, number and timing of previous doses or previous infection, and risk factors (predominantly age) for myocarditis and pericarditis following vaccination.
Adolescents and younger adults have a lower age-related risk of severe COVID-19, and a comparatively higher risk of myocarditis following vaccination. The risk of myocarditis is highest in people aged 16-30 years (peak 16-18 years), and is higher in males than females12–14. The risk of myocarditis appears to be lower after COVID-19 booster doses in comparison with dose 2 of the primary course and is lower following Pfizer COVID-19 vaccine as compared with Moderna COVID-19 vaccine in some contexts14,15. See COVID-19 vaccination – Guidance on myocarditis and pericarditis after COVID-19 vaccines for more information.
Any age-appropriate COVID-19 vaccine, including original (ancestral virus-based) vaccines, are expected to boost neutralising antibodies and thereby provide additional protection against any infection and longer lasting protection against severe disease.
However, most immunogenicity studies have shown a trend towards BA.4/5-based vaccines inducing higher neutralising activity against Omicron subvariants (including BQ.1 and XBB) than original vaccines or BA.1-containing vaccines4,16–18, although a few studies reported similar neutralising antibody titres when comparing the responses to different vaccines19. Early published and preprint data on whether these increases in neutralisation activity translate into measurable differences in clinical protection suggest a small advantage in vaccine effectiveness with bivalent vaccines over original vaccines in preventing hospitalisation and death20,21. However, further confirmatory studies are awaited. Early data suggest that the vaccine effectiveness of BA.1-based bivalent booster vaccines is similar to ancestral-based booster doses, but potentially with slower waning of protection6,22.
For more information on which vaccines are available for each age group refer to the COVID-19 vaccine doses and administration webpage. Bivalent Original/Omicron BA.1 vaccines are only registered for use in people aged 18 years and over. The Pfizer bivalent Original/Omicron BA.4/5 vaccine is registered for use from 12 years of age.
There are currently insufficient data to determine the timing of any additional future COVID-19 booster doses. However it is likely, as with influenza vaccine, that regular doses of COVID-19 vaccine will be needed to maintain immunity against SARS-CoV-2 over years to come, particularly for those at highest risk of severe disease. ATAGI will continue to monitor data on the duration of protection from booster doses, as well as on new circulating virus variants or subvariants, and will provide updated vaccine advice as required.
1. World Health Organization. Tracking SARS-CoV-2 variants. https://www.who.int/activities/tracking-SARS-CoV-2-variants
2. New South Wales Ministry of Health. NSW Respiratory Surveillance Report - week ending 07 January 2023. https://www.health.nsw.gov.au/Infectious/covid-19/Documents/weekly-covi…
3. Jiang XL, Zhu KL, Wang XJ, et al. Omicron BQ.1 and BQ.1.1 escape neutralisation by omicron subvariant breakthrough infection. Lancet Infect Dis. 2023;23(1):28-30. doi:10.1016/S1473-3099(22)00805-2
4. Kurhade C, Zou J, Xia H, et al. Low neutralization of SARS-CoV-2 Omicron BA. 2.75. 2, BQ. 1.1, and XBB. 1 by parental mRNA vaccine or a BA. 5-bivalent booster. Nature Medicine. Published online 2022:1-1.
5. Karyakarte R, Das R, Dudhate S, et al. Clinical Characteristics and Outcomes of Laboratory-Confirmed SARS-CoV-2 Cases Infected with Omicron subvariants and XBB recombinant variant. medRxiv. Published online 2023:2023-01.
6. UK Health Security Agency. COVID-19 vaccine surveillance report. Week 2: 12 January 2023. https://assets.publishing.service.gov.uk/government/uploads/system/uplo…
7. Arbel R, Peretz A, Sergienko R, et al. Effectiveness of the bivalent mRNA vaccine in preventing severe COVID-19 outcomes: An observational cohort study. Available at SSRN 4314067. Published online 2023.
8. Nafilyan V, Ward IL, Robertson C, Sheikh A, National Core Studies—Immunology Breakthrough Consortium. Evaluation of Risk Factors for Postbooster Omicron COVID-19 Deaths in England. JAMA Network Open. 2022;5(9):e2233446. doi:10.1001/jamanetworkopen.2022.33446
9. Vo AD, La J, Wu JTY, et al. Factors Associated With Severe COVID-19 Among Vaccinated Adults Treated in US Veterans Affairs Hospitals. JAMA Network Open. 2022;5(10):e2240037. doi:10.1001/jamanetworkopen.2022.40037
10. United Kingdom Government, Department of Health and Social Care. JCVI statement on the COVID-19 vaccination programme for 2023: 8 November 2022. Published January 27, 2023. https://www.gov.uk/government/publications/covid-19-vaccination-program…
11. Hansen CH, Friis NU, Bager P, et al. Risk of reinfection, vaccine protection, and severity of infection with the BA. 5 omicron subvariant: a nation-wide population-based study in Denmark. The Lancet Infectious diseases. Published online 2022.
12. Yasuhara J, Masuda K, Aikawa T, et al. Myopericarditis After COVID-19 mRNA Vaccination Among Adolescents and Young Adults: A Systematic Review and Meta-analysis. JAMA Pediatrics. 2023;177(1):42-52. doi:10.1001/jamapediatrics.2022.4768
13. Ling RR, Ramanathan K, Tan FL, et al. Myopericarditis following COVID-19 vaccination and non-COVID-19 vaccination: a systematic review and meta-analysis. Lancet Respir Med. 2022;10(7):679-688. doi:10.1016/S2213-2600(22)00059-5
14. Pillay J, Gaudet L, Wingert A, et al. Incidence, risk factors, natural history, and hypothesised mechanisms of myocarditis and pericarditis following covid-19 vaccination: living evidence syntheses and review. BMJ. 2022;378:e069445. doi:10.1136/bmj-2021-069445
15. Yechezkel M, Mofaz M, Painsky A, et al. Safety of the fourth COVID-19 BNT162b2 mRNA (second booster) vaccine: a prospective and retrospective cohort study. The Lancet Respiratory Medicine. Published online 2022.
16. Davis-Gardner ME, Lai L, Wali B, et al. Neutralization against BA. 2.75. 2, BQ. 1.1, and XBB from mRNA Bivalent Booster. New England Journal of Medicine. 2023;388(2):183-185.
17. Zou J, Kurhade C, Patel S, et al. Improved Neutralization of omicron BA. 4/5, BA. 4.6, BA. 2.75. 2, BQ. 1.1, and XBB. 1 with bivalent BA. 4/5 vaccine. BioRxiv. Published online 2022:2022-11.
18. Collier A ris Y, Miller J, Hachmann NP, et al. Immunogenicity of BA. 5 Bivalent mRNA Vaccine Boosters. New England Journal of Medicine. Published online 2023.
19. Wang Q, Bowen A, Valdez R, et al. Antibody Response to Omicron BA. 4–BA. 5 Bivalent Booster. New England Journal of Medicine. Published online 2023.
20. Andersson NW, Thiesson EM, Baum U, et al. Comparative effectiveness of the bivalent BA. 4-5 and BA. 1 mRNA-booster vaccines in the Nordic countries. medRxiv. Published online 2023:2023-01.
21. Lin DY, Xu Y, Gu Y, et al. Effectiveness of bivalent boosters against severe omicron infection. New England Journal of Medicine. Published online 2023.
22. UK Health Security Agency. COVID-19 vaccine surveillance report. Week 48: 1 December 2022. https://assets.publishing.service.gov.uk/government/uploads/system/uplo…