A decision of the Court of Appeal of England and Wales has confirmed the strict line that UK courts are (like the European Patent Office) taking in relation to the assessment of patent priority claims.
It is of course common practice for a patent applicant to file an initial application in its home jurisdiction and then to follow up within one year with an updated application filed internationally. The later application “claims priority” from the earlier one, and to the extent that the invention claimed in the later application was disclosed in the earlier one, its effective date (the “priority date”) is the date of filing of the earlier application. So long as the claim to priority is, and remains, valid, any public disclosures of the invention made between the first filing and the second do not form part of the state of the art and are therefore of no relevance to the patentability of the invention.
So far, so simple. But what happens if the definition of the invention in the later application does not match what was disclosed in the earlier one? Or if the definition of the invention is modified during the course of examination, for instance in order to differentiate from the prior art, and the modified definition has no counterpart in the application from which priority was claimed? In these circumstances, the patent claim may not be entitled to the claimed priority date. Instead, the effective date of the claim is the date on which the later application was filed, and any disclosures made earlier than that (intervening publications) could be damaging prior art.
In Novartis v Hospira  EWCA Civ 1663, the Court of Appeal has rejected an appeal against a judgement of Arnold J. in the Patents Court from March 2013, in which he held that the claim in suit was not entitled to priority and that, as a consequence of a publication made after the filing of the application from which priority had been claimed, the claim lacked novelty.
The patent concerned the use of a particular medicament (zoledronate) for the treatment of a particular condition (osteoporosis) at a particular dosage (about 2 to 10mg) and a particular dosing interval (about once a year). All of these features were disclosed in the priority application, but crucially neither the Patents Court nor the Court of Appeal accepted that they were disclosed in combination. Since it is the particular combination of features that constitutes the invention in respect of which priority was claimed, and since the priority application did not disclose that combination “directly and unambiguously” (language taken from the leading authority at the EPO, namely Decision G2/98 of the Enlarged Board of Appeal), the claim was not entitled to priority. In this case, all parties were agreed that if the claim was not entitled to priority, then it would lack novelty, and that is what the Court held.
So what lessons can be learned from this case? There are several, though setting them out in this fashion may be easier than implementing them in the real world:
a) The disclosure of an initial application intended to establish a priority date should be as complete as possible. The days in which it was possible to establish an effective date for an invention by the filing of a sketchy provisional application are gone. The practice prevalent in many Universities of filing patent applications that are little more than draft academic papers is particularly risky.
b) Even after an initial application has been filed, disclosures of the invention should be avoided until after the final application has been lodged. Changes to the definition of an invention may be unavoidable (as well as being unforeseeable), and no matter how fulsome the disclosure of the initial application may be, it cannot be guaranteed that a claim granted after several years of examination will be entitled to priority. Where there has been no intervening publication, a claim that is not entitled to priority may at least still be novel and inventive.
c) Where additions are made to the specification of the later application, relative to the content of the earlier application from which priority is to be claimed, the claims of the later application should be drafted so far as possible in such a way that they are entitled to priority.
d) Similarly, where amendments to the claims are made later, the entitlement of the amended claims should be a factor taken into account when formulating those amendments.
It is all too easy to assume that a claim to priority is valid, and the filing of the initial application may give applicants a false sense of security. The Courts (and the EPO) are taking a strict view, with potentially serious consequences, and this issue is therefore one to which all applicants should attach high priority!