How long does it take for prior art to become common general knowledge?

Merck Sharp & Dohme Corp v Teva UK Ltd, [2011] EWCA Civ 382 is a case in the Court of Appeal for England and Wales concerning the validity of a patent for an invention for treating glaucoma. Last Thursday the Chancellor of the High Court, Sir Andrew Morrit, handed down his judgment with which Richards and Patten LJJ agreed. At first instance, Floyd J had held the patent invalid for obviousness and for containing added matter ([2009] EWHC 2952 (Pat)). Only the obviousness question was before the Court of Appeal.


The problem was that the prior art that appeared to make the claimed invention obvious had been published only six days before the priority date. The appellant based its argument on the superficially logical and attractive proposition that this wasn't long enough for the skilled person (in this case a team) to do anything with it. In determining whether there is an inventive step the judge must assume the mantle of the skilled addressee - and if he did so, MS&D argued, he would still have been blundering about in the dark trying to make sense of this latest piece of art when the application was filed. (The fact that the paper in which the prior art was published was written by a team three of whom were connected with MS&D doesn't seem to have made any difference.) The Chancellor rejected this approach, saying at para 36:

There is no additional time requirement… If by reference to the relevant state of the art the invention is obvious then it matters not that it may take time to perform the necessary routine tests. It is a matter of simple comparison between the relevant art and the claimed invention.

The rules governing who can get a patent for an invention are necessarily a little arbitrary. The "first to file" rule involves a bit of tough justice - but no workable alternative would be any better, although some might prefer the uncertainty of "first to invent". The novelty test doesn't look at what the inventor actually knew, or even what he or she (or they) might reasonably have known: what matters is what is in the state of the art.

But when it comes to inventive step, it is a matter of considering the skilled addressee's knowledge. Importing the notion of the skilled addressee necessarily means that not everything in the state of the art is relevant. Perhaps on the facts of this case it made no difference that this piece of prior art would take some time to percolate through to the notional skilled addressee, but it seems to me that in determining what that person might know the time it could take to assimilate some new learning might logically postpone the inclusion of that learning in the individual's knowledge, and to deem that to happen immediately is a bit of rough justice too far.