Evaluability assessment of the antimicrobial resistance (AMR) subscription model

Antimicrobial drugs such as antibiotics and antivirals are used to treat infections and so limit the spread of disease. However, the more they are used, the more likely it is for microbes causing infection to develop resistance to their effects (antimicrobial resistance or AMR). While the best approach to addressing AMR is to reduce the use of antimicrobials, there is also a need for new drugs. However, making new antimicrobials is expensive. To make it more attractive for drug companies to invest in such developments, the NHS in England has begun testing a new payment model for antimicrobials (a ‘subscription model’). Instead of paying drug companies on the basis of how many antimicrobials are sold, the NHS pays them a fixed yearly fee. This guarantees access to important new antibiotics, while reducing pressure to overuse them.

In 2022, the NHS bought two antibiotics through the scheme, and this was expanded further in 2024, with £1.6 billion committed by the government over 16 years. Although the scheme was seen as a success in practice, there has not yet been an independent evaluation to understand whether it is achieving its aims.

We conducted a so-called ‘evaluability assessment’ to better understand what the subscription model is trying to achieve and how success should be measured and to explore how the model could best be evaluated in the future.

We conducted a rapid review of academic, policy and grey literature on antimicrobial subscription models and related pull incentives. Findings from the review were used to develop an initial Theory of Change, setting out how the subscription model is expected to work, the assumptions underpinning its implementation, and the outcomes it aims to achieve.

We then interviewed national and international stakeholders from government, industry, academic and policy organisations to explore perceptions of the model, its intended outcomes, underlying assumptions, and how success might be measured. We also held a workshop with representatives from the Department of Health and Social Care, NHS England and NICE to validate and refine the Theory of Change, identify priorities for future evaluation, and discuss available data sources and evidence gaps.

Drawing on evidence from all stages of the study, we produced a final Theory of Change describing the mechanisms through which the subscription model is expected to influence antimicrobial innovation, market sustainability, the global adoption of pull incentives, antimicrobial stewardship, and health outcomes, alongside the enablers and barriers that may shape whether and how these outcomes are realised. We also identified potential indicators, metrics and data sources that could support a future evaluation of the model. No formal patient and public involvement activities were undertaken, as the study focused on policy design, implementation and evaluation rather than patient experiences.

The study found that many of the subscription model’s intended outcomes, particularly impacts on innovation, antimicrobial resistance (AMR) burden, and broader health outcomes, are likely to emerge only over longer-time horizons. These outcomes are influenced by multiple interacting factors, making attribution to the subscription model difficult and limiting the feasibility of meaningful short-term evaluation.

We also identified several methodological and practical challenges for future evaluation, including limited data availability, small patient populations eligible for subscription-model antibiotics, and difficulties measuring broader societal benefits.

The study identified two areas that appear most amenable to meaningful early evaluation: changes in market behaviour (including developer and investor engagement, tender submissions, and antimicrobial pipeline activity) and the model’s influence on the international adoption of pull incentives. These areas have observable indicators, accessible data sources, and more plausible attribution to the subscription model than many of its longer-term objectives.

Stewardship, health system impacts, AMR outcomes, and value for money remain important areas for future evaluation but are likely to require longer follow-up periods, greater utilisation of subscription-model antibiotics, and further development of data collection and monitoring systems before they can be robustly assessed.