21 September 2023

Approaches to plausibility at the EPO and in the UK

Over the past few months, recent decisions concerning the notion of plausibility and the ability to rely on evidence not provided at the time of filing have been released both at the European Patent Office (EPO) and in the UK. This article will explore the rulings from both jurisdictions and determine the extent to which the two are aligned.

Brief background

The concept of plausibility does not appear in either the Patents Act or the European Patent Convention. Nonetheless, in recent years it has become a major talking point, forming the basis of several decisions across both jurisdictions. Plausibility generally concerns the idea that something (e.g., a technical effect) must have been plausible to the skilled person at the time of filing, and largely relates to what was disclosed in the application as originally filed.

Europe – G2/21

The decision stemmed from European patent 2484209, which relates to an insecticide made up of a particular combination of compounds. Specifically, claim 1 of the granted patent relates to a composition comprising two insecticidal compounds – thiamethoxam and ‘a compound of formula 1a.’ A template for formula 1a is shown below.

The claim itself defines R1-R5 and X as particular chemical groups, and also excludes three particular compounds from falling under the scope of formula 1a. Although the cited prior art had disclosed thiamethoxam and compounds of the aforementioned formula 1a individually, no combination of the two had been recited. With regard to inventive step, the applicant argued that the technical effect of this specific combination was a synergistic effect of the compounds against two particular species of moth and provided data to support this.

The granted patent was opposed, during which the opponent filed new data which appeared to contradict the proprietor’s arguments by suggesting that a combination of thiamethoxam and chlorantraniliprole (a compound that falls within the scope of formula 1a) did not have a synergistic effect against one of the two moth species. This would mean that the technical effect was not achieved across the whole scope of the claims.

In response to this, the proprietor provided post-published evidence in the form of data allegedly showing that the synergistic effect was achieved against a third species of moth. The Opposition Division was satisfied that the technical effect could therefore be reformulated as providing a synergistic effect against the third moth species. While the Opponent did not dispute this, they did argue that this synergistic effect against the third species of moth was not plausible from the application as originally filed and so requested that the post-published evidence be dismissed.

The subsequent decision to reject the Opposition was appealed, with the case eventually making its way up to the Enlarged Board of Appeal (EBA) in a bid to ascertain the extent to which the post-published evidence could be relied on.

Ahead of the ruling, it was anticipated that the EBA would align their decision with one of the three so-called standards of plausibility, which are described below.

Standards of plausibility

  • No plausibility – this is the lowest bar for plausibility; in fact, it rejects the concept all together. If this standard were to be applied, it would mean that post-published evidence could be considered regardless of detail and regardless of whether a technical effect would have been plausible. Such an approach is inconsistent with the EPO’s problem-solution approach, and so it was never envisaged that this standard would be applied.
  • Ab initio implausibility – this is an intermediate bar, which states that post-published evidence can only be disregarded if there is a legitimate doubt that the technical effect on the filing date of the application. As long as the technical effect would have been plausible, the evidence can be admitted. In such an instance, the burden of proof would rest on an Opponent to show that the technical effect was not plausible.
  • Ab initio plausibility – this is the highest bar for plausibility, which states that post-published evidence can only be taken into account if there is legitimate reason to believe that the technical effect had been achieved at the filing date. The default assumption is that the effect is implausible, and the onus would be on the applicant to show that the effect was in fact plausible at the time of filing.

The below table helps to summarise what types of evidence can be admitted according to the three different standards.

The Board of Appeal provided the following questions to the EBA.

  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 the post-published evidence?
  • If the answer is yes, can the 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?

In other words, should the ‘ab initio plausibility’ standard be applied?

  • If the answer to the first question is yes, can the 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?

In other words, should the ‘ab initio implausibility’ standard be applied?

In response to question 1, the EBA concluded that the principle of free evaluation of evidence could not be used to disregard evidence per se, since doing so could deprive a party of the basic legal procedural right to be heard and to provide evidence. As such, evidence submitted to prove a technical effect relied upon for inventive step may not be disregarded solely on the ground that such evidence was post-published.

Turning to questions 2 and 3, the EBA (perhaps wisely) steered away from the concept of plausibility. Noting that the term itself “does not amount to a distinctive legal concept or a specific patent law requirement under the EPC”, the EBA deemed plausibility to be nothing more than a ‘generic catchword’ and instead focused the issue at hand towards precisely what the skilled person would have understood from the application at the time of filing, rather than what they might have considered credible.

With this in mind, the EBA came to the conclusion that a technical effect may be relied upon for inventive step if the skilled person, having the common general knowledge in mind and based on the application as originally filed, would consider the technical effect as being encompassed by the technical teaching and embodied by the same originally disclosed invention. On this basis, the patentee was able to rely on their post-published evidence concerning the third moth species and so the claims were found to be inventive. The appeal was therefore dismissed.

A key point to note from this is that there is no requirement for such a technical effect to be directly supported by data in the original application – an effect that is only supported by post-published evidence may still be sufficient to be considered as encompassed by the technical teachings within.

The outcome is largely positive news for applicants, since it has avoided some of the difficulties that may have arisen from a verdict falling directly within the constraints of the ab initio plausibility standard. The fact that post-published evidence can be relied on will be particularly welcome news to applicants for whom early filings are a necessity. Nonetheless, the ruling does swing the burden of proof back to the applicant, and it will therefore be crucial for applicants to strike a balance between getting applications on file promptly and ensuring that there is sufficient data to support any technical assertions made later on during prosecution.

UK – Sandoz v BMS ([2023] EWCA Civ 472)

Prior to this decision, the benchmark for plausibility in the UK was Warner-Lambert v Actavis, in which it was ruled that that a patent specification must render plausible, at the filing date of the application, that the technical effect embodied in the claimed invention can be achieved. The ruling laid the ground for the UK Courts to treat plausibility as a valid legal concept (despite the fact that it does not appear in the Patents Act) and has ensured that it remains part of the common vernacular among UK attorneys.

However, as described above, the EPO decision G 2/21 seemingly renounced plausibility as a legal concept. This left the UK Courts in an awkward position whereby the Supreme Court deemed plausibility to be a legal concept and requirement for grant, yet the EPO deemed the opposite. It was therefore hoped that the present ruling might be able to reconcile these two decisions.

The case stemmed from European patent EP(UK) 1427415. Claim 1 was directed towards apixaban, an anticoagulant medical compound. This compound is a factor Xa inhibitor, and the alleged technical effect of the claim was the compound’s use against thromboembolic disorders (e.g., blood clots).

The specification itself had no specific data to directly support apixaban’s usefulness against such disorders. Indeed, the closest the description came to this was a section in which it recites that “a number of compounds of the present invention were found to exhibit a Ki of <10 µM, thereby confirming the utility of the compounds of the present invention as effective Xa inhibitors.” While this generic statement suggests that a large number of compounds (including apixaban) could be used as inhibitors of factor Xa, there was no data specifically showing apixaban’s capabilities in this regard.  Nonetheless, the application proceeded to grant, after which a revocation action was brought by Sandoz and Teva on the grounds of sufficiency and inventive step, due to the supposed lack of plausibility.

The High Court deemed that apixaban’s use as a factor Xa inhibitor would not have been plausible to the skilled person at the time of filing, and therefore found the patent to lack sufficiency and inventive step. BMS appealed, arguing that “in the case of a claim to a single chemical compound, there is no requirement that the specification makes it plausible that the compound is useful.” BMS further argued that “it is sufficient that the specification discloses the structure of the compound and a method of synthesis and contains an assertion of potential utility for the compound, provided that that assertion is not manifestly speculative or wrong.”

Rather than aligning with the EPO on the matter of plausibility, the Court of Appeal conceded that, at least in this instance, it was bound by the Supreme Court decision in Warner-Lambert v Actavis. The recent EBA decision in Europe did not merit a departure from the precedent set in the UK Courts. Arnold LJ deemed that the earlier Supreme Court majority decision in Warner-Lambert was equivalent to an ab initio plausibility test (with the minority decision relating to an ab initio implausibility test), and despite considering several of the points raised in G 2/21, held that the plausibility standard set out in Warner-Lambert should remain the same. With reference to G 2/21, he commented that the EBA decision should be treated as an endorsement of the ab initio plausibility standard that formed the basis of the majority decision in Warner-Lambert, using this as justification not to deviate from the earlier Supreme Court ruling.

Arnold LJ subsequently upheld the decision of the High Court and ruled that post-published data could not be used as a substitute for sufficient disclosure in the specification. In his remarks, he stated that the description “gives the skilled team no reason for thinking that there is a reasonable prospect that the assertion will prove to be true”, adding that “it is therefore speculative.

Whether or not BMS attempt to elevate the matter to the Supreme Court remains to be seen, but in any case, the idea of plausibility in UK patents will remain a hot topic. The Supreme Court is due to hear the appeal of Fibrogen v Akabia in March 2024, which will no doubt build upon the decisions made in Sandoz vs BMS.

For the time being, it appears that rather than aligning, the plausibility approaches in the UK and in Europe are diverging further. In particular, the UK approach appears to be less favourable to applicants than its European counterpart, and applicants are advised to ensure that they have sufficient data in their specifications to back up any technical assertions that may be made during prosecution.