Based on the provided sources, it is difficult to determine the exact duration of the Yervoy discount. However, the information suggests that the availability of the discount may be influenced by various factors.

The first source, Drug Patent Watch, provides information on the patent status of Yervoy, which is an immunotherapy drug used in the treatment of melanoma. As of the time of the report, the patent for Yervoy was set to expire in October 2028 [1]. This information indicates that the drug may still be under patent protection, which could affect the availability and pricing of the medication.

The second source, an article from PMLive, discusses how discounts played a role in persuading the National Institute for Health and Care Excellence (NICE) to recommend Yervoy for the treatment of skin cancer. The article mentions that the manufacturer of Yervoy offered a confidential discount to the National Health Service (NHS) in the UK, which led to the recommendation by NICE [2]. While the article does not specify the duration of the discount, it suggests that the availability of the discount may be subject to negotiations between the manufacturer and healthcare authorities.

The third source, a research article published in the National Center for Biotechnology Information (NCBI) database, discusses the cost-effectiveness of Yervoy and other immunotherapies for the treatment of melanoma. The study highlights the high cost of these treatments and the challenges they pose for healthcare systems [3]. While the article does not provide specific information about the duration of the discount, it suggests that the pricing and availability of Yervoy may be influenced by factors such as cost-effectiveness evaluations and reimbursement decisions made by healthcare authorities.

In conclusion, the available sources do not provide a clear answer regarding the duration of the Yervoy discount. The information suggests that the availability and pricing of Yervoy may be influenced by factors such as patent status, negotiations between the manufacturer and healthcare authorities, and cost-effectiveness evaluations. It is recommended to consult with healthcare providers or the manufacturer for the most up-to-date information on the availability and pricing of Yervoy.

Sources:
[1] Drug Patent Watch: https://www.drugpatentwatch.com/p/biologics/tradename/YERVOY
[2] PMLive: http://www.pmlive.com/pharma_news/discounts_persuade_nice_to_recommend_skin_cancer_drugs_yervoy_and_zelboraf_445335
[3] NCBI: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3538397/