Australia’s COVID-19 vaccine journey: progress and future perspectives

Introduction

The strict public health measures implemented across Australia during the early phase of the COVID-19 pandemic kept rates of SARS-CoV-2 infection extremely low, until most of the population had received at least two doses of an approved vaccine. Since the relaxation of these measures in late 2021, a combination of waning immunity post-vaccination and the highly infectious and immunoevasive nature of the Omicron variants has driven waves of infection. The initial emergence of Omicron was characterised by the dominance of a single subvariant, BA.1, which was rapidly replaced by BA.2 and then BA.5 by mid-2022¹ (Fig. 1a). Subsequently, infection waves in Australia have consisted of a diverse mix of Omicron subvariants that has been termed the Omicron ‘soup’ (Fig. 1a). Thus, immunity to SARS-CoV-2 across the Australian population is highly variable, depending on both the number of vaccine doses received or breakthrough infections.

Fig. 1.

SARS-CoV-2 variants and vaccination in Australia. (a) Overview of SARS-CoV-2 variants circulating in Australia over time as percentage of total infections. Only representative variants shown for clarity. Data from CoVariants.org. (b) Timing of the vaccine rollout in Australia. The date of provisional approval for each vaccine (by company and variant) is approximated on the timeline. Full details can be found at www.tga.gov.au/products/covid-19/covid-19-vaccines/covid-19-vaccines-regulatory-status.

The COVID-19 vaccine rollout in Australia and its effect on population immunity

Over 95% of adults in Australia had received the initial two doses of an approved COVID-19 vaccine by the end of 2021. Over time, the levels of SARS-CoV-2 neutralising antibodies (NAbs) naturally decline. This, coupled with the emergence of viral variants carrying mutations that diminish antibody recognition, contributes to a reduction in vaccine effectiveness. Australian researchers were the first to establish a correlation between the efficacy of COVID-19 vaccines and the titres of NAbs targeting the SARS-CoV-2 spike protein.^2–4 To counter waning immunity, ‘booster’ vaccine doses are recommended by the Australian Technical Advisory Group on Immunisation (ATAGI); 3rd vaccine doses were initially introduced at the end of 2021 for high-risk groups, before being expanded in 2022 to all adults whose second dose had been received more than 6 months prior. Clinical data from the Australian population have shown that such booster vaccine doses can restore NAb levels after waning, broaden cross-recognition of SARS-CoV-2 variants and improve protection against symptomatic infection and severe disease.⁵ Importantly, Australia served as a distinctive case for evaluating booster efficacy, as prior to Omicron, the Australian population had low rates of previous SARS-CoV-2 infection but high levels of vaccination. In older Australians (65+ years), vaccination is highly effective against COVID-19 mortality, although effectiveness wanes quickly with time since last dose.⁶ Accordingly, ATAGI recommends an additional booster dose for those 75+ years, if their previous vaccination was more than 6 months prior.⁷ However, uptake of booster doses has been slow; as of 6 December 2023, only 22% of those aged 75+ years in Australia have received a COVID-19 booster within the last 6 months, leaving a large number of vulnerable individuals at risk.⁷

Currently, population immunity to SARS-CoV-2 in Australia is being shaped by a mix of responses to both vaccination and infection,⁸ largely with the Omicron subvariants (Fig. 1a). The ability of Omicron subvariants to cause breakthrough and re-infections can be attributed to key mutations within the viral spike protein that render them antigenically distinct from the ancestral spike antigen used in the original COVID-19 vaccines. Therefore, to improve responses against these subvariants updated bivalent (ancestral+BA.1 and ancestral+BA.5) booster vaccines were developed (Fig. 1b). Bivalent booster vaccines were provisionally approved in Australia in August 2022, and were recommended by ATAGI as the booster of choice in early 2023. A study of Australians aged over 65 showed bivalent boosters provide better protection against mortality from the diverse Omicron subvariants XBB and BA.2.75 than ancestral-based vaccines.⁹ Owing to the persistent global dominance of the Omicron subvariants, particularly the recombinant XBB lineage, monovalent XBB.1.5 booster vaccines were developed and approved for use in Australia in October 2023. Currently there are limited studies describing the efficacy of XBB.1.5 monovalent vaccines; however, current data suggest the XBB lineage, which includes EG.5 variants, could be soon replaced by JN.1 variants.¹⁰ Therefore, the development of next-generation COVID-19 vaccines that can provide pan-variant protection, as well as more durable responses, are required to reduce SARS-CoV-2 infection rates.

Australia’s contribution to the next-generation of SARS-CoV-2 vaccines

Australia’s dependence on ‘imported’ COVID-19 vaccines significantly influenced the pace of the initial vaccine rollout, highlighting vulnerabilities in our sovereign vaccine manufacturing capabilities.¹¹ Nevertheless, the pandemic has catalysed increased investment, both domestically and globally, in advancing not only COVID-19 vaccines but also tools to combat diseases with pandemic potential. This investment, coupled with the high quality of Australian science, has given rise to several research programs addressing these issues, as outlined in Table 1 and discussed below.

Conclusions

Australia made many valuable scientific contributions during the COVID-19 pandemic that have strengthened our vaccine development and manufacturing capabilities. Continued research and investment in this field will be critical to ensure we are prepared for future pandemic threats.

Data availability

No new data were generated or analysed during this study.

Conflicts of interest

The authors declare that they have no conflicts of interest.

Declaration of funding

The authors’ COVID-19 vaccine studies are supported by the Coalition for Epidemic Preparedness Innovations and the Medical Research Future Fund.