In a recent study posted to the medRxiv* pre-print server, researchers evaluated the cost-effectiveness of Australia’s coronavirus disease 2019 (COVID-19) booster vaccination strategy.
Despite implementing a strict COVID-zero policy, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) new variant of concern (VOC) Omicron alone surged COVID-19 cases in Australia to as high as six million in six months since November 2021. The country had already vaccinated around 90% of its population with two doses by this time. Although the mortality rate was much lower than before, Omicron still claimed 5,000 lives in Australia.
About the study
In the present study, researchers used a decision-analytic Markov model to evaluate Australia's COVID-19 booster vaccination strategy during the Omicron wave. Assessing the economic impact of the booster strategy at the population level helped the researchers derive insights into the country's overall COVID-19 prevention and mitigation strategy.
The team conducted an economic evaluation survey around three months after mass-level administration of the second dose of a messenger ribonucleic acid (mRNA)-based COVID-19 vaccine from a healthcare perspective.
The study model simulated COVID-19 progression among all the individuals over 16 years for approximately 180 days, focusing primarily on Omicron transmission. The team defined the vaccine efficacy (VE) as short-term and long-term because studies have indicated that VE of BNT162b2, mRNA1273, and Covishield COVID-19 vaccines wanes in about three months.
The model comprised 11 health states, and the researchers estimated transition probabilities between them using the formula p = 1 − e - r. Note, that r here denotes the daily transition rate. The model explored three case scenarios for its simulations. The first was a counterfactual scenario where no one received any booster shots. In the second, booster coverage was 69.4% by 5 May 2022, and in the third scenario, all the eligible individuals received booster shots on time.
The international vaccine access center provided VE data for Omicron infections. Additionally, the team referred to the 'Our World in Data’ website for daily reported COVID-19 cases in Australia. They integrated this data with the COVID-19 vaccination information in Australia to compute variations in the population incidence of COVID-19.
The team pooled the short-term and long-term VE estimates of the primary and booster vaccination using 11 eligible studies. Based on the VE variations, the team developed a mathematical model that estimated the distributions of clinical COVID-19 stages in both vaccinated and unvaccinated individuals. The team computed the direct medical cost of each COVID-19 case by multiplying the unit cost of the medical services by the duration of each disease stage. They also derived the summation of medical costs of all the COVID-19 cases with varying severity.
The medical services comprised general practitioner (GP) consultation, hospitalization, and intensive care unit (ICU) admission. The vaccine and its administration cost were A$53 and A$20 per dose, respectively. Likewise, the cost of reverse transcription-polymerase chain reaction (RT-PCR) and rapid antigen tests (RAT) for COVID-19 was A$85 and A$13 per person, respectively. Additionally, the team considered the estimates of pricing models for COVID-19 treatments published by the Institute for Clinical and Economic Review.
The assumed discount rate for both cost and quality-adjusted life-years (QALYs) was 3% per year. The researchers compared the incremental costs and incremental QALYs for the booster vaccination strategy. They computed the incremental cost-effectiveness ratio (ICER), keeping a willingness-to-pay (WTP) threshold of ICER below A$50,000. The team also estimated the net monetary benefit, benefit-cost ratio, and cost per death saved.
Lastly, the team performed probabilistic sensitivity analyses (PSA) based on 100,000 simulations to estimate the probability of the booster strategy being cost-effective across several cost-effectiveness thresholds. They varied the evaluation period from 90 to 180 days to report the corresponding benefit-cost ratio and ICER.
In a counterfactual scenario with no booster vaccinations, the authors noted a direct medical cost of A$5.31 billion. The current booster strategy reduced the direct medical cost by A$1.28 billion while incurring an additional vaccination cost of A$0.88 billion. Since this strategy fetched a net monetary benefit of A$0.43 billion, it appeared cost-effective and even gained 670 QALYs over 180 days.
The authors also noted that while the current booster strategy prevented one COVID-19 death at the cost of A$655,077, implementing a universal booster strategy would reduce this cost further to A$476,123 to prevent one COVID-19 death.
The PSA also showed the cost-effectiveness of the current booster strategy, including a cost-saving probability of 71.2%. Varying evaluation periods from 90 to 180 days in this cost-effectiveness analysis indicated the need for greater than 140 days evaluation period for the current booster strategy to be cost-effective. Moreover, the benefit-cost ratio of a booster strategy was 0.55 in a 90-day evaluation period. It implied that a dollar worth of investment on the booster saved A$0.55 in treating fewer hospitalized COVID-19 patients, and this ratio increased from 0.55 to 1.45 upon extending the evaluation period to 180 days.
The study had several important findings. One of the key findings was that the current booster vaccination strategy was highly cost-effective, and the universal vaccination strategy further saved cost.
The current booster strategy saved 1.32 million new SARS-CoV-2 infections, 65,170 hospitalizations, 6,927 ICU admissions, and 1,348 deaths in 180 days, with a cost-benefit ratio of 1.45 and a net monetary benefit of A$0.43 billion. A lower benefit-cost ratio of 1.45 in Australia was primarily attributable to the higher cost of mRNA-based COVID-19 vaccines in Australia compared to the United States.
Further, the universal vaccination strategy, i.e., administering a booster as soon as an individual met the eligibility criteria, saved an additional 1.42 million additional new cases, 73,753 hospitalizations, 8,081 ICU admissions, and 1,706 deaths, with a cost-benefit ratio of 1.95 and a net monetary benefit of A$1.46 billion.
Because the short-term VE against Omicron infections of a booster shot was 62% and reduced to 46% after 90 days; therefore, a rapid scale-up to a universal booster vaccination strategy was highly cost-effective and successfully combated the Omicron epidemic in Australia. However, for the booster strategy to be as cost-effective as predicted, the epidemic needed to persist for 140 days.
The study findings also pointed out that when low-cost antiviral drugs would be accessible to the general public in the future, the cost-effectiveness of the booster strategy declines further.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Rui Li, Hanting Liu, Christopher K Fairley, Jason J Ong, Yuming Guo, Zhuoru Zou, Li Xie, Guihua Zhuang, Yan Li, Mingwang Shen, Lei Zhang. (2022). mRNA-based COVID-19 booster vaccination is highly effective and cost-effective in Australia. medRxiv. doi: https://doi.org/10.1101/2022.05.08.22274797 https://www.medrxiv.org/content/10.1101/2022.05.08.22274797v1