By interlocutory decision T 116/18 of October 11, 2021, Technical Board of Appeal 3.3.02 referred questions to the Enlarged Board of Appeal (hereinafter the Enlarged Board) to determine whether evidence, such as experimental data, not having been public before the filing date of the patent in suit and having been filed after that date (post-published evidence), may be considered for the acknowledgement of inventive step when the proof of the technical effect rests exclusively on the post-published evidence.

Indeed, in the field of chemistry and life sciences, it is common to provide experimental data illustrating the existence of a technical effect associated with the feature that distinguishes the claimed invention from the closest related prior art. However, the subsequent demonstration of the existence of a technical effect raises concerns about its plausibility at the time the patent application was filed.

The referring Enlarged Board identified three main lines of case law regarding the evaluation of evidence that becomes available to the public after the filing of a patent application:

1) Ab initio plausibility: post-published evidence could be taken into consideration only if, given the information in the patent application as filed and the common general knowledge at the filing date, the skilled person would have had reason to assume the purported technical effect to be achieved. In this line of case law, experimental data or a scientific explanation in the application as filed commonly serve as reasons which justify this assumption (T1329/04, T609/02, T488/16)
2) Ab initio implausibility: post-published evidence can only be disregarded if the skilled person would have had legitimate reasons to doubt that the purported technical effect can in fact not be achieved (T919/15, T578/06, T2015/20)
3) No plausibility: this third line rejects the so-called plausibility concept on the ground that ignoring post-published evidence would be incompatible with the problem-solution approach, which sometimes requires the technical problem to be reformulated in light of documents not cited in the patent (T2371/13).

Therefore, the Enlarged Board was tasked with determining whether evidence published after filing may be disregarded on the ground that the effect rests exclusively on such evidence, thereby contravening the principle of free evaluation of evidence. If so, the Enlarged Board must determine whether the concept of ab initio plausibility or ab initio implausibility should be applied.

In its decision, the Enlarged Board of Appeal qualifies the principle of free evaluation of evidence as a universally applicable principle in assessing any means of evidence by a board of appeal under the European Patent Convention (hereinafter EPC).

It follows that evidence submitted by a patent applicant or proprietor to prove a technical effect relied upon for acknowledgement of inventive step may not be disregarded solely on the ground that such evidence had not been public before the filing date of the patent and was filed after that date.

The Enlarged Board also held that the plausibility concept is not a specific concept or requirement according to the EPC. It is merely a formulation developed in case law.

The relevant standard for the reliance on a purported technical effect when assessing whether the claimed subject-matter involves an inventive step concerns the question of what the skilled person, with the common general knowledge in mind, would understand at the filing date from the patent application as originally filed as the technical teaching of the claimed invention. The technical effect relied upon, even at a later stage, needs to be encompassed by that technical teaching and to embody the same invention, because such an effect does not change the nature of the claimed invention.

Finally, although it was not seized of this question, the Enlarged Board addressed the issue of sufficiency of disclosure of second medical use claims. The Enlarged Board held that the plausibility concept could be used in this case. Indeed, as the therapeutic effect is a technical feature of the claim, sufficiency of disclosure is required to prove it.

The Enlarged Board concluded that the scope of reliance on post published evidence is much narrower under sufficiency of disclosure compared to the situation under inventive step. In order to meet the requirement that the disclosure of the invention be sufficiently clear and complete for it to be carried out by the person skilled in the art, the proof of a claimed therapeutic effect has to be provided in the application as filed, in particular if, in the absence of experimental data in the application as filed, it would not be credible to the skilled person that the therapeutic effect is achieved. A lack in this respect cannot be remedied by post-published evidence.