Article 4 of Council Directive 85/374/EEC of 25 July 1985 on the approximation of the laws, regulations and administrative provisions of the Member States concerning liability for defective products must be interpreted as not precluding national evidentiary rules such as those at issue in the main proceedings under which, when a court ruling on the merits of an action involving the liability of the producer of a vaccine due to an alleged defect in that vaccine, in the exercise of its exclusive jurisdiction to appraise the facts, may consider that, notwithstanding the finding that medical research neither establishes nor rules out the existence of a link between the administering of the vaccine and the occurrence of the victim’s disease, certain factual evidence relied on by the applicant constitutes serious, specific and consistent evidence enabling it to conclude that there is a defect in the vaccine and that there is a causal link between that defect and that disease. National courts must, however, ensure that their specific application of those evidentiary rules does not result in the burden of proof introduced by Article 4 being disregarded or the effectiveness of the system of liability introduced by that directive being undermined.

Thus, firstly, national courts must first ensure that the evidence adduced is sufficiently serious, specific and consistent to warrant the conclusion that, notwithstanding the evidence produced and the arguments put forward by the producer, a defect in the product appears to be the most plausible explanation for the occurrence of the damage, with the result that the defect and the causal link may reasonably be considered to be established.

Secondly, those same courts must ensure that the principle that it is for the victim to prove, through all means of proof generally allowed under national law and, as in the present case, inter alia through the production of serious, specific and consistent evidence, that there is a defect in the vaccine and a causal link, remains intact. This requires the court to safeguard its own freedom of assessment in determining whether such proof has been made out to the requisite legal standard, until such time as, having examined all the evidence adduced by both parties and the arguments exchanged by them, it considers itself in a position to draw a definitive conclusion on the matter, having regard to all the relevant circumstances of the case before it (see, by analogy, judgment of 9 November 1983, San Giorgio, 199/82, EU:C:1983:318, paragraph 14).

In the present case, evidence such as that relied on in the main proceedings relating to the temporal proximity between the administering of a vaccine and the occurrence of a disease and the lack of personal and familial history of that disease, together with the existence of a significant number of reported cases of the disease occurring following such vaccines being administered, appears on the face of it to constitute evidence which, taken together where applicable, may lead a national court to consider that a victim has discharged his burden of proof under Article 4 of Directive 85/374. That could be the case inter alia where that evidence leads the court to consider, first, that the administering of the vaccine is the most plausible explanation for the occurrence of the disease and, second, that the vaccine therefore does not offer the safety that one is entitled to expect, taking all circumstances into account, as provided for in Article 6 of that directive, because it causes abnormal and particularly serious damage to the patient who, in the light of the nature and function of the product, is entitled to expect a particularly high level of safety (see, to that effect, judgment of 5 March 2015, Boston Scientific Medizintechnik, C‑503/13 and C‑504/13, EU:C:2015:148, paragraph 39).

(see paras 37, 38, 41, 43, operative part 1)