Unravelling the Riddles of Secret Prior Art in India and elsewhere

Patents are granted for inventions that are novel and involve an inventive step. Any information or material that is publicly available or published before the filing of a patent application is known as “prior art” and this forms the basis on which novelty and inventive step is determined. For a prior patent application to be considered prior art for a subsequent patent application, the prior patent application should have been published before the filing of the subsequent patent application. A prior patent application that was filed before the filing of a subsequent patent application but published only after the filing of the subsequent patent application, is not prior art in many jurisdictions. The jurisdictions that do consider such patent applications as prior art often refer to them as ‘secret prior art’.

Secret prior art poses a peculiar dilemma for applicants and administrators alike. On the one hand, if secret prior art were considered valid, then the applicant of the subsequent application would be unfairly disadvantaged. Being unaware of the prior patent application, the applicant would have no opportunity to distinguish their invention from the prior invention in the application to avoid any potential subject-matter overlap. The threat of secret prior art derailing a patent application could dampen inventive activity.

On the other hand, if secret prior art were not considered, it would result in double-patenting i.e. granting a patent twice for the same invention. This has many implications, including the possibility of multiple infringement proceedings and that one of those inventions may never be worked at all. Another troubling consequence is that since the later applicant for the same invention would also obtain patent rights, this would result in an unfair extension of time of protection available for the same invention to that applicant.

‘Whole contents’ approach

Broadly, there are two approaches to treating secret prior art. The first is ‘the whole contents approach’, which takes into consideration the entire disclosure, i.e., the description and the claims of the first application. This is followed in Europe (EP), Japan (JP), and the United States (US), among others. However, divergences exist even here. EP and JP only consider secret prior art for assessing the novelty of the subsequent application. For instance, Article 54(3) of the European Patent Convention (EPC) clarifies that:

earlier applications (secret prior art) are part of the state of the art only when considering novelty and not when considering inventive step and by the “content” of a European application is meant the whole disclosure, i.e. the description, drawings and claims’.

This requires there to be a direct overlap between the subject matter of the secret prior art and subsequent applications, and therefore, minor modifications to the invention in the subsequent application would be overlooked.

The US, however, adopts a more stringent approach. Under 35 U.S.C. §103(a), and U.S.C §102, the prior art effect of secret prior art applications is considered for the determination of both novelty and non-obviousness.

‘Prior claim’ approach

The second approach to treating secret prior art is the ‘prior claim’ approach, where only the claims of the subsequent application are taken into consideration. India follows this approach where only the claims of a prior filed application are considered. Section 13(b) of the Indian Patents Act 1970 (‘the Act’) states:

The examiner … shall make investigation for the purpose of ascertaining whether the invention so far as claimed in any claim of the complete specificationis claimed in any claim of any other complete specification published on or after the date of filing of the applicant’s complete specification, being a specification filed in pursuance of an application for a patent made in India and dated before or claiming the priority date earlier than that date’.

Prior claiming can also be a ground for opposing a patent application pre-grant under Section 25(1)(c) of the Act, and a ground for revocation of a patent in a post-grant opposition (Section 25(2)(c) or Section 64(a) of the Act).

The prior claiming approach has been elaborated in Pfizer Products Inc. v. The Controller of Patents & Designs (OA/2/2016/PT/MUM). here, the Intellectual Property Appellate Board (IPAB) clarified that:

In order to have valid objection about anticipation by prior claiming, the following has to be established (section 13(1)(b)):

  1. that there is an invention for which an application for patent has been made in India (hereinafter referred to as ‘the first application’)
  2. the second invention for which a patent has been granted is “claimed in any claim” of the complete specification of the first application.
  3. The first application is published after the priority date of the claim of the patentee.
  4. The claim of the first application has a priority date that is earlier than the claim of the patentee.

The IPAB further clarified that ‘for the purpose of prior claiming, “the claims” of the Indian Prior art have to be mapped with the claims of the Indian applications/patents’.

Recent decisions at the Delhi High Court have also discussed the prior-claiming approach in detail. In Astrazeneca AB & Anr. v. Intas Pharmaceuticals Ltd. [FAO (OS) (Comm) 9/2020, decision dated 11 November 2020], the Court clarified that for claim construction and to ascertain whether claims of the prior and subsequent application are overlapping in scope, one can rely upon the specification to understand the scope of the claims in light of the disclosure under Sections 10(4) and 10(5) of the Act. This was echoed in the 20 July 2021 decision of the Delhi High Court in Astrazeneca AB & Anr. v. Intas Pharmaceuticals Ltd. [FAO(OS) (COMM) 139/2020], to determine whether the compound Dapagliflozin was disclosed in Indian Patent No. 205147, with a priority date of 12 October 1999, versus Indian Patent No. 235625, which had a priority date of 20 May 2002, which specifically claimed the compound.


In certain cases, the. the secret prior art and the subsequent application may be filed by the same applicants. This scenario is treated differently by different jurisdictions.

Under the EPC, no special provisions exist for secret prior art by the same applicants. Prior art can be cited against the novelty of the subsequent application even if the applicants are the same.

The US takes a slightly different position. 35 U.S.C. §103(c) provides that if a secret prior art is cited under Section 102(e), (f), or (g) against a subsequent application, but is owned by or assigned to the same person, then prior art would not be considered for the determination of non-obviousness (inventive step). However, the prior art could be cited for non-statutory type of double patenting, for which a terminal disclaimer would overcome such an objection. This arrangement also addresses the issue of time-period extension for the same invention.

A similar route is adopted in Japan, where under Article 29.2 of the Patent Act, a secret prior art can be cited against the novelty of a subsequent patent application, provided that the applicants of both the applications are not the same, i.e., in case of self-collision, the secret prior art cannot be cited against the subsequent application.

In India, recent judgements point to a trend where the threshold for the determination of non-obviousness, prior-claiming, and use before the date of filing of patent application is higher when the applications in question are filed by the same inventors and/or applicants. The Delhi High Court in Astrazeneca AB & Anr. v. Intas Pharmaceuticals Ltd. [FAO(OS) (COMM) 139/2020, decision dated 20 July 2021] reasoned that when the inventor is the same, the tests for “obvious to a person skilled in the art” and “anticipation by publication” and “use before the date of filing of patent application with complete specification” should be considered in the context of the ‘person in the know’ as, in such a scenario, it could be assumed that the inventor might be aware of the second invention while applying for a patent for the prior application. The Court also said that if a case for infringement was made for both the earlier and the latter filed application by the same patentee, then it could imply that both applications disclose the same subject matter. The Court said that the patentee cannot claim infringement for both applications, and subsequently argue that the applications do not relate to overlapping subject matter, purely with the intention of extending the exclusive rights for the same compound.

This decision was relied upon by the same Court in Sulphur Mills Limited vs Dharmaj Crop Guard Limited & Anr. [CS(COMM) 1225/2018 & CC(COMM) 9/2019, decision dated 2 August 2021] where the Court held that if the applicant of a first application is shown to have been ‘in the know’ of the invention of a subsequent application, then this could be relied on for the determination of obviousness.

This clearly stringent approach in cases of self-collision, where the threshold to demonstrate inventive step is set higher, appears to be directed at rewarding truly inventive inventions, and prevent frivolous and repetitive patenting of inventions overlapping in scope, or where trivial changes are made to seek longer patent terms. The true test of these decisions, however, will lie in how the Indian Patent Office tackles future patent applications in the context of secret prior art.


The treatment of secret prior art in various jurisdictions falls at different points on a spectrum. These become especially relevant when filing multi-jurisdiction applications, as the same application may be prosecuted differently depending on where it is filed. Divergences exist where the new application is filed by the same applicant of the secret prior art too. As for India, it stands out from other jurisdictions in following the ‘prior claiming’ approach for prosecuting applications with respect to secret prior art (and not the ‘whole contents’ approach followed in EP, JP and US). Additionally, in cases of self-collision, India appears inclined to impose a higher threshold for the determination of obviousness, which could require additional planning.