The loss of valuable patent rights due to a formality happened to Alexion Pharmaceuticals, Inc. which prompted them to inquire with the EPO Enlarged Board of Appeal how strictly these formal rules should be applied. In its long-awaited decision on 10 October of this year, the Enlarged Board stated that the right of priority can be transferred with minimal formalities and that the patent applicant claiming priority is, in principle, entitled to it.

The Paris Convention of 1883 provides that a patent applicant or his legal successor retains the right of priority for one year. This provision allowed inventors, in an era of slow postal service, to submit their inventions internationally to local patent offices in a large number of countries. An interim publication of the invention within the priority year does not harm the later patent application, as it retains the original filing date by invoking the priority right.

After hearing from a large group of stakeholders, the Enlarged Board ruled that the EPO itself has the authority to decide whether a European patent applicant can claim the priority right. The basis for this is found in the European Patent Convention (EPC), which acts as an autonomous 'law'. This means that proceedings before the EPO do not require recourse to the national courts of the 39 contracting states. This simplifies the patent grant procedure and increases legal certainty.

In addition, the Enlarged Board found that the formal procedure for claiming priority provides sufficient safeguards to assess whether a person who successfully completes these formalities is entitled to priority. To claim priority, one must submit both a copy of the unpublished patent application and a certified copy from the patent office of first filing. This can only be done with the consent and cooperation of the original applicant who holds the priority right to be transferred.

Finally, the Enlarged Board found that the formalities required for a valid transfer of priority rights cannot be more stringent than the most lenient requirement within the EPC treaty states. Since in Germany an implied agreement (called "konkludente Einigung") is sufficient for a valid transfer, the Enlarged Board held that no written or signed agreement is required. In practice, this makes the priority right an ancillary right closely related to the transfer of the patent application itself.