Background
In 2007, the priority review voucher (PRV) was implemented in the US to incentivize research and development (R&D) for tropical diseases. The PRV is issued by the US FDA and grants a quicker review to manufacturers upon successful development of a product for a disease eligible for the program.

Objective
The objective of this analysis was to assess whether the PRV has incentivized R&D (measured as clinical trial activity) for the intended tropical diseases.

Method
We used a difference-in-difference-in-differences (DDD) strategy by exploiting variation in its implementation across diseases and registries around the world. Clinical trials were retrieved from the World Health Organization International Clinical Trials Registry Platform for the years 2005–2019.

Results
We found a positive, but not statistically significant, effect of the PRV on stimulating R&D activity. Delayed effects of the policy could not be found.

Conclusion
Our findings, which were robust across a series of robustness tests, suggest that the PRV program is not associated with a trigger in innovation for neglected diseases and therefore should not be considered as a stand-alone solution. It should be supplemented with other government measures to incentivize R&D activity. To increase the value of the program, we recommend that the PRV only be awarded to novel products and not to products that have already been licensed outside the US. Doing so would restrict the number of vouchers awarded and slow down their ongoing market depreciation. Finally, we propose that product sponsors be required to submit an access plan for PRV-awarded products.