Avoiding pitfalls in priority applications

Filing a priority application is often the first formal step in protecting an invention. It gives rise to so-called “priority rights”, which allow the applicant (or their successor in title) to file further applications in other countries and have them treated as if they were filed on the same date as the priority application (known as the “priority date”) for the assessment of patentability.

To benefit from the priority date, the later filings must be made within 12 months of filing the priority application. They can take the form of national applications filed directly in each country of interest, or more commonly, a single international (PCT) application that is later converted into national applications.

Whether an applicant can benefit from the priority date depends on the validity of their right to claim priority. An invalid priority claim becomes problematic when there is a public disclosure relevant to the invention that occurs after the priority date but before the filing date of the subsequent application. In such cases, an invalid priority claim can be fatal if the later filing lacks novelty or inventiveness over the disclosure.

A weak priority filing can cost you your patent if the invention is disclosed before your main filing.

It may be tempting to file a priority application based on preliminary data, an early idea or at minimal cost, with the assumption that you have additional time to further develop the invention or evaluate its commercial potential before incurring costs for drafting a more complete application. This can be an attractive approach for those with constrained budgets, such as university technology transfer departments, where delaying costs until a project’s commercial viability becomes clearer is often necessary.

However, while this approach may seem pragmatic, failing to adequately describe your invention in a carefully drafted priority application can have serious consequences. An incomplete or poorly drafted priority application can fail to provide the support needed for a valid priority claim.

What the law requires
A core requirement for a valid priority claim is that the invention claimed in the subsequent application must be the “same” as that in the priority application. However, interpretations of what constitutes the same invention vary significantly between jurisdictions.

At the European Patent Office (EPO), for the priority application and subsequent European application to be considered to disclose the same invention, the invention claimed in the subsequent European application must be “directly and unambiguously” disclosed in the priority application.

The EPO is notoriously strict in this assessment. Even small differences between the wording in the priority application and the subsequent application can result in the EPO concluding that the applications do not disclose the same invention and that the priority claim is invalid.

The EPO takes a strict approach – the invention claimed in the subsequent European application must be “directly and unambiguously” disclosed in the priority application.

For an invention to be directly and unambiguously disclosed, the application must also provide an enabling disclosure of the invention (i.e., it must include enough technical detail for a skilled person to carry out the invention). A priority application lacking key technical details required to work the invention may not be considered to disclose the invention at all.

The United States Patent and Trademark Office (USPTO) is usually more flexible than the EPO in assessing whether the priority application and subsequent US application are directed to the same invention. In China, Japan, and South Korea, patent offices take a similar, but slightly more lenient approach, to the EPO.

Due to the differences in approach, if you intend to seek patent protection in multiple countries, it is important that your priority and subsequent applications are drafted to withstand scrutiny regardless of whether a strict or flexible approach is taken in assessing the validity of the priority claim.

Tips for getting your priority application right
A carefully prepared priority application can help reduce the risk of unnecessary delays and costs later in the patent process. The tips below explain what you should aim to include in your priority application and how to help ensure it stands up to scrutiny later on:

• Include a full disclosure of the invention: describe the key features of the invention in detail and explain how someone can put the invention into practice. For example, if possible, include details of worked examples of your invention such as a prototype or characterisation data for new chemical compounds. For chemical inventions, it is also important to include detail of synthetic routes for any new compounds. Chemical structures alone may not be considered an enabling disclosure.

• Include details of variants and broader definitions of the invention (e.g. a general formula for a family of compounds): if the invention is described narrowly and only in the context of specific experiments or a prototype in your priority application, a broader definition introduced in your subsequent application may not be entitled to the priority date. For example, if your priority application discloses only a specific compound but your subsequent application claims a broader class of compounds, the broader claim will very likely not be considered “directly and unambiguously” disclosed in the priority application. The priority claim for the broader class of compounds is then very likely to be considered invalid.

• Include fallback positions around commercially relevant embodiments of the invention: by including fallback positions in both your priority and subsequent applications, you ensure that any narrower embodiments of your invention are directly and unambiguously disclosed in both applications and therefore entitled to the priority date. Without fallback positions entitled to the priority date, you may be forced to abandon commercially useful claims if the broader scope is found unallowable and the fallback positions lack novelty or inventiveness over an intervening disclosure.

• If available, include experimental data demonstrating any advantages associated with the invention: including experimental data is particularly important for chemical or biological inventions, where it is often essential to show that the invention works and that a particular technical effect is achieved. Without experimental data, it is possible that your priority application may be found to not provide an enabling disclosure of your invention.

• If the invention is developed further after filing the priority application, file a second priority application providing details of the developments or modifications: a subsequent application can claim priority from multiple priority applications, provided it is filed within 12 months of the earliest priority application. Filing a further priority application as soon as possible including details of any developments or modifications ensures that the earliest date possible is established for assessing patentability.

• Work with a patent attorney who is experienced in drafting patent applications in your technical field: a well-drafted priority application should support a valid priority claim and place your subsequent applications in the strongest possible position. Filing an incomplete application, or simply an invention disclosure form or draft journal article, is unlikely to provide adequate support for a valid priority date for claims that offer broad and commercially useful protection for your invention.

Final points
If you cut corners and omit information in your first priority filing, do not assume that shortcomings can be fixed later or that missing details can be added. If you intend to seek patent protection in multiple countries or regions, it is important that your priority application meets the standards of the strictest ones, such as Europe and China. By investing time and effort upfront and working with an experienced patent attorney, you can greatly improve your chances of securing commercially valuable patent protection.

This article does not constitute legal advice. Specialist legal advice should be sought in relation to specific circumstances. For advice, please get in touch with your usual contact at Abel + Imray or bd@abelimray.com.