The EPO Enlarged Board of Appeal has finally published its long-awaited “plausibility” decision (G2/21). On the face of it, it seems that the concept of “plausibility” is here to stay, but the good news for applicants and patentees is that the Enlarged Board have confirmed that late-filed data must be considered when assessing inventive step.

The concept of “plausibility” is not a formal ground for refusing an application or revoking a granted patent at the EPO. Instead, it has been developed through case law, in the assessment of sufficiency or inventive step, to assess whether a purported effect - such as treatment of a particular disease - is credible to the skilled person based on the disclosure of the application as filed and the common general knowledge in the art.

Historically, the Technical Boards of Appeal have taken two separate and distinct approaches to assessing plausibility. The stricter approach, applying an ab initio plausibility standard, requires some positive indication in the application as filed that the invention achieves the effect it purports to achieve. The more lenient approach has been characterized as ab initio implausibility. This approach generally allows post-published evidence to be considered unless there is a reason to doubt that the effect would have been achieved. In other words, post-published evidence should be accepted to support an alleged effect unless the alleged effect is actively implausible from the application as filed.

When the Technical Boards diverge in this way, the Enlarged Board is asked to intervene and decide on the correct approach. In this case, the Enlarged Board was asked to consider the following questions:

1. Should an exception to the principle of free evaluation of evidence be accepted in that post-published evidence must be disregarded on the ground that the proof of the effect rests exclusively on post-published evidence?

2. If the answer is yes, can post-published evidence be taken into consideration if, based on the information in the patent application in suit or the common general knowledge, the skilled person at the filing date of the patent application in suit would have considered the effect plausible (ab initio plausibility)?

3. If the answer to the first question is yes, can post-published evidence be taken into consideration if, based on the information in the patent application in suit or the common general knowledge, the skilled person at the filing date of the patent application in suit would have seen no reason to consider the effect implausible (ab initio implausibility)?

The Preliminary Opinion of the Enlarged Board suggested that the answer to the first question should be “no”, indicating that no evidence “must” be disregarded and that the principle of the “free evaluation of evidence” should apply (i.e., confirming that parties have a right to be heard in accordance with Article 113(1) EPC). With regard to questions 2 and 3, the Preliminary Opinion favored the more lenient ab initio implausibility standard.

The wait for the final decision from the Enlarged Board has been several months, leading to some concern that the Enlarged Board was intending to back-track on their Preliminary Opinion. Luckily, however, this has not been the case, and the Enlarged Board last week confirmed the lower, ab initio implausibility standard.

The key legal judgements are as follows:

1. Evidence submitted by a patent applicant or proprietor to prove a technical effect relied upon for acknowledgement of inventive step of the claimed subject matter may not be disregarded solely on the ground that such evidence, on which the effect rests, had not been public before the filing date of the patent-in-suit and was filed after that date.

2. A patent applicant or proprietor may rely upon a technical effect for inventive step if the skilled person, having the common general knowledge in mind, and based on the application as originally filed, would derive said effect as being encompassed by the technical teaching and embodied by the same originally disclosed invention.

This is good news for applicants, particularly in the pharmaceutical space where applications need to be filed early, and often before comprehensive data is available. Nevertheless, the question of plausibility remains. Applicants and proprietors will therefore need to convince the EPO that the technical effect of the invention was plausible to the skilled person at the priority date.

Interestingly, the judgement limits the discussion of plausibility to inventive step and the question of whether the invention in hand would have been obvious to the skilled person at the effective date of the patent or patent application. Sufficiency is the requirement for a patent or patent application to “disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art”. Sufficiency and inventive step can often become intertwined since both concepts rely on the knowledge of the skilled person, and we have seen the Technical Boards of Appeal linking sufficiency with the concept of plausibility. For example, in T 609/02, the key claim at issue was a Swiss- type medical use claim for the treatment of arthritis and other disorders. The Board of Appeal found that there was no evidence, indicating that the application as filed only contained a “vague indication of a possible medical use”. Since it was not plausible from the application as filed that the intended medical treatment could be achieved, the claim was held to be insufficient. One fundamental difference between inventive step and sufficiency at the EPO is that a lack of sufficiency cannot generally be remedied with late- filed data. We will therefore have to wait and see if there will be a second referral to the Enlarged Board to clarify the EPO’s position on plausibility in the context of sufficiency.

Since late-filed data cannot be used to rectify a lack of sufficiency, it is questionable how much the EPO’s plausibility decision will impact filing strategy. Anyone drafting an application will still need to weigh up the need to file early and balance that against whether the available data is adequate to meet the sufficiency requirements in Europe. More evidence may be necessary where the claims are broader, the technical field is younger and the technology in question is unpredictable.

For applications that have already been filed, it is undoubtedly good news that late-filed data will be considered by the EPO within the context of inventive step. Nevertheless, applicants and proprietors can still be in a precarious position. Proving the state of the art and common general knowledge at the priority date is far from trivial. It is worth remembering that the EPO is unlikely to accept an affidavit as proof of the state of the art. Thus, applicants and proprietors need to lean on textbooks, technical standards and review articles as proof of the common general knowledge. As many find out the hard way, finding a document that says just enough - but not so much as to be detrimental - can be tricky.

Furthermore, decisions of the Enlarged Board are only binding during EPO proceedings. EPC member states often look to the Enlarged Board for guidance on issues but are not bound by its rulings. The concept of plausibility was considered in detail by the UK Supreme Court in the Warner-Lambert decision, which set the bar for plausibility in the UK relatively high (i.e., an ab initio plausibility approach). Given the complex relationship between the UK and Europe post-Brexit, it seems highly unlikely that the UK courts will now switch to the EPO’s more lenient ab initio implausibility standard. It is worth noting, however, that the Warner-Lambert decision centered on a question of sufficiency of a second medical use claim. Since the UKIPO assessment of inventive step does not use the EPO’s so-called “problem and solution” approach, it remains to be seen if plausibility will become a factor in future UK court decisions relating to inventive step, and if a different standard might be applied there.

Beyond Europe, China does not have a directly analogous concept of “plausibility”. However, recent changes to Chinese patent law in light of a trade deal with the US means that the Chinese Patent Office (SIPO) now allows supplemental data to establish patentability for pharmaceutical inventions. Post-filed data can be used to show unexpected effects in support of inventive step, but only if such effects are disclosed in the application as filed.

In the US, whether or not late-filed data is permitted depends on the nature of the objection from the USPTO. In recent years, there has been a shift towards more strict examination of the written description and enablement requirements. In general, such defects can only be cured with late-filed data when there is a “hook” in the application - to use the language of the EPO, when there is a reason for the skilled person to believe that such data is merely showing a technical effect derivable from the application.

It therefore remains wise to aim for a higher standard, particularly if patent protection in the UK and US is sought. Applicants will still need to carefully consider the level of evidence required for their claimed effect to be considered plausible, dependent on the specific facts of the case.

Originally printed in IAM on April 21, 2023.