Effects on National Rights
Where an opposition (or any appeal from it) results in an amended patent, then after the end of the proceedings an amended specification is republished by the EPO and the patentee must file a translation into the relevant language at the patent office of each designated state whose national law so requires.
Where the opposition or appeal results in revocation of the patent, then it is revoked in each designated state as if it had never existed; no damages or other remedies can subsequently be obtained for the period prior to revocation (although in many countries, such as the UK, damages awarded in cases finally concluded before the revocation cannot be refunded as such cases are regarded as res judicata). No judicial review before the national courts can be used to resurrect a patent revoked by the EPO.
Where the opposition or appeal results in the patent being maintained (whether unamended or in an amended form), further attacks on the patent may be made before the national courts or patent offices of the designated states. Such attacks are operative only to revoke or limit the patent in the state concerned.
The grounds for attack before the national authorities are mainly identical to the possible grounds of opposition; many national courts are extremely reluctant to overturn EPO Appeal Board decisions on identical facts, and so it is advisable to include a fresh ground of attack over those made in the opposition.
The EPC itself does not prevent even an unsuccessful opponent from subsequently attacking the same patent before the national authorities on the same grounds. Some Contracting States regard an opponent as being estopped from so doing, although others do not.
In principle, the burden of proof of invalidity rests with the opponent, and so where the evidence conflicts the benefit of any doubt should be given to the patentee, particularly in view of the "asymmetrical" nature of opposition proceedings. In practice, the EPO often resists finding "doubt" of this kind.