Cost-Effectiveness of Vaccination Strategies to Control Future Mpox Outbreaks in England
Authors: Zhang Xu-Sheng , Niyomsri Siwaporn , Mandal Sema , Mohammed Hamish , Mindlin Miranda , Dugbazah Bennet , Adjei Solomon , Charlett Andre , Edney Jessica , Sugars Elliot , Kliner Merav , Mannes Trish , Jewitt Ellie , Gilbert Lorna , Moazam Samihah , Dewsnap Claire , Phillips David , Amirthalingam Gayatri , Ramsay Mary E. , Vickerman Peter , Walker Josephine 
Published: August 2024

Background

In 2022, a global outbreak of mpox occurred among gay and bisexual men who have sex with men (GBMSM). In England, the outbreak was controlled through reductions in sexual risk behaviour and vaccination of high-risk GBMSM. However, mpox continues to circulate and so future outbreaks could occur. We evaluated the most cost-effective vaccination strategy to minimise future mpox outbreaks among GBMSM in England.

Methods

A mathematical model of mpox transmission among GBMSM was developed to estimate the costs per quality-adjusted-life-year (QALY) gained for different vaccination strategies starting in 2024 (20-year time-horizon; 3.5% discount rate; willingness-to-pay threshold £20,000/QALY). The model was calibrated using English surveillance data from the 2022 outbreak and two community surveys. Reactive vaccination (only during outbreaks) and pre-emptive vaccination (continuous routine) strategies targeting high-risk GBMSM were compared to no vaccination. Baseline projections assumed vaccine effectiveness of 78%/89% for 5/10 years with 1/2 doses at £160/dose. Costs were estimated for case management, vaccination and public health responses (PHR) during an outbreak.

Findings

All vaccination strategies reduced costs and gained QALYs compared to no vaccination. Continuous pre-emptive vaccination (daily rate 41 doses) was most cost-effective, saving £39.56 million and gaining 547.6 QALYs over 20-years. Threshold analyses suggested vaccination of high-risk GBMSM is cost-effective if the vaccine costs <£701/dose. Pre-emptive vaccination remains the optimal strategy across numerous sensitivity analyses, but the optimal vaccination rate can vary. Reactive vaccination only becomes more cost-effective when PHR costs are not included.

Interpretation

Pre-emptive vaccination of high-risk GBMSM is a cost-saving strategy to prevent future mpox outbreaks.

Funding

NIHR

Extended funding statement

This study was funded by the NIHR Health Protection Research Unit in Behavioural Science and Evaluation at University of Bristol NIHR200877, in partnership with UK Health Security Agency (UKHSA). The views expressed are those of the author and not necessarily those of the NIHR, the Department of Health and Social Care, or UKHSA.

Research in context

Evidence before this study

The global outbreak of mpox in 2022 predominantly affected gay, bisexual, and other men who have sex with men (GBMSM). After a steep rise in cases over May to June 2022, the rate of cases of mpox decreased dramatically after July 2022, thought to be due to the roll-out of vaccination programmes in many countries and reductions in sexual risk behaviour among GBMSM. Despite this decline in cases, new infections of mpox have occurred among GBMSM in many countries in 2023, raising concerns that new outbreaks could occur especially if levels of vaccine-induced protection reduce over time. We searched PubMed, bioRxiv and medRxiv for articles published from beginning May 2022 to 28 June 2024 with the following keywords: ((“monkeypox” OR “mpox” OR “mpx”) AND (“model” OR “modelling” OR “modeling”) AND (“vaccine” OR “vaccination” OR “cost-effectiveness” OR “cost-effective”)). Although this search identified many articles involving transmission modelling that assessed the impact of various interventions on mpox transmission, only eight provided insights on what is needed to prevent future outbreaks, just one considered the cost implications of vaccinating for mpox, and none evaluated the cost-effectiveness of vaccination. Existing model analyses have evaluated what interventions are needed to control outbreaks showing that future outbreaks could be controlled by vaccinating close contacts of cases and individuals in large sexual networks, as well as pre-emptively vaccinating high-risk individuals prior to outbreaks occurring. None of these analyses used detailed data to calibrate their models to actual settings, reducing their real-world relevance. Conversely, other model analyses undertook detailed modelling for specific settings (Canada, Netherlands and England), and showed that existing levels of vaccine roll-out may have reduced the magnitude of future outbreaks. However, these analyses did not model possible future vaccination strategies. The only economic analysis for mpox compared the costs of vaccination to not vaccinating the general population in Jeddah, Saudi Arabia, suggesting that vaccination costs more than not vaccinating, although vaccinating the general population is an unrealistic strategy. Unfortunately, this economic analysis used implausible data (respiratory infection contact rates) to simulate the transmission of mpox, did not use recent data to estimate transmissibility, did not focus on GBMSM, and used very little data on the health-related costs of mpox disease.

Added value of this study

This economic analysis extends our understanding of what is needed to control future outbreaks of mpox among GBMSM in England and other settings. Combining a previously validated model of mpox infection in England with real data on the costs of care for mpox, vaccination and public health responses, we undertook an economic analysis to evaluate the most cost-effective future vaccination strategy to prevent future mpox outbreaks. We model either reactive (only vaccinate during outbreaks) or pre-emptive (routine vaccination irrespective of outbreaks) vaccination strategies targeting high-risk GBMSM. Our analyses show that all modelled vaccination strategies are likely to be cost-saving and improve quality of life compared to not vaccinating, with continuous pre-emptive vaccination at a low rate (daily rate 41 doses) being the most cost-effective strategy. This finding is robust over most sensitivity analyses with mpox vaccination remaining cost-effective if the vaccine price is less than £701 per dose.

Implications of all the available evidence

Ongoing importation of new sexually transmitted mpox cases in many non-endemic countries means that these countries need to be prepared for future mpox outbreaks if immunity levels fall or if the pool of unvaccinated people increases to a large extent. Our analyses give robust evidence that mpox vaccination is a cost-saving strategy for minimizing the likelihood of future mpox outbreaks in England and other comparable countries. These findings have been used as evidence by the UK Joint Committee on Vaccination and Immunisation to recommend a pre-emptive (routine) vaccination programme of high-risk GBMSM through sexual health services in the UK. Other countries should seriously consider similar strategies to prevent future outbreaks.