BISTLINE, Justice.

In 1979, plaintiff child Kevin Toner, then three months old, received a vaccination of Tri-Immunol, a drug manufactured by defendant Lederle Laboratories and designed to immunize children against diphtheria, pertussis, and tetanus. Thereafter, Kevin suffered a rare condition of the spine known as transverse myelitis. The affliction permanently paralyzed Kevin from the waist down. Plaintiffs brought suit against Lederle in Idaho state court, but the suit was removed to federal district court on the basis of diversity jurisdiction. At trial, the jury found that Lederle's vaccine has caused Kevin's paralysis and found Lederle negligent, although it rejected plaintiffs' strict liability and breach of warranty claims. Lederle appealed the judgment to the United States Court of Appeals for the Ninth Circuit. Rather than render a decision, pursuant to I.A.R. 12.1 (Supp. 1986) the Court of Appeals certified and this Court accepted two controlling questions of Idaho law. These questions center on the role in Idaho strict liability and negligence law of the so-called "unavoidably unsafe" product doctrine, as described in comment k of Restatement (Second) of Torts § 402A (1965) (quoted infra, p. 12).

I. BACKGROUND

Toner found much with which to disagree in the Court of Appeals' summary of the facts. Two of the points of contention Toner raised we will set out in footnotes to our quotation of the Court of Appeals' opinion. As we do not have the trial record before us, we must use the Court of Appeals' summary as background to our decision. However, as we will explain below, the posture of the case, which includes a standing jury verdict that Lederle was negligent but that the vaccine was not in a "defective condition unreasonably dangerous to persons," requires certain factual presumptions regardless of the Court of Appeals' recitation.

The Court of Appeals states the facts as follows:

In 1979, Kevin Toner, then a three-month-old infant, was vaccinated with Tri-Immunol and suffered a rare condition of the spine known as transverse myelitis, the cause of which is unknown. As a result of the affliction, Kevin is permanently paralyzed from the waist down. His parents commenced litigation in Idaho state court, and appellant removed the case to federal court on the basis of diversity of citizenship. 28 U.S.C. § 1441 (1982). The suit was tried to the jury on theories of strict liability, negligence, breach of warranty of merchantability, and failure to warn. Appellees withdrew the failure to warn claim before the case was submitted to the jury. The jury found that the pertussis component of the vaccine had caused Kevin's paralysis; although in a special verdict the jury rejected the strict liability and breach of warranty claims, it found appellant negligent and assessed damages of $1,131,200.

In the early years of this century, pertussis was one of the leading causes of death in children. In recent years, however, the widespread availability of vaccines such as that marketed by defendant has virtually eradicated the disease. An instructive, brief description of common vaccines is found in an opinion by the Second Circuit, Ezagui v. Dow Chemical Corp., 598 F.2d 727, 731 (2d Cir. 1979), and we rely upon that description for the following background explanation.

By introducing an antigenic factor into the body, vaccines stimulate the production of antibodies that protect against disease. Some infectious organisms, such as those causing diphtheria and tetanus, excrete soluble toxins insoluble by medical research. The toxin is inactivated with formaldehyde and transformed into a toxoid. The toxoid is then used in a vaccine, as it can immunize against disease by stimulating the production of antibodies in the recipient, even though it has lost its own poisonous qualities.

This is not the case, however, with vaccines such as Tri-Immunol. Tri-Immunol is a so-called whole cell vaccine because it contains whole killed pertussis organisms. The whole organism is used because the pertussis organism contains fifteen or sixteen different antigens, and medical science has yet to isolate the one that stimulates protection against the disease. See Tinnerholm v. Parke, Davis Co., 411 F.2d 48, 50 (2d Cir. 1969). Courts that have addressed the issue of liability for adverse reactions to the DPT vaccine have commented that "the bacterial organism which causes pertussis is so complex as to make impossible the isolation and deactivation of the toxin or poison." Ezagui, 598 F.2d at 731; accord Tinnerholm, 411 F.2d at 50. Because of this difficulty, at the time of Kevin Toner's vaccination, the whole cell pertussis vaccine was the only pertussis vaccine licensed by the Food and Drug Administration (FDA) for use in the United States. It remains the only licensed vaccine today.

The whole cell pertussis vaccine is neurotoxic and can cause adverse reactions. These reactions are of two types: local and severe. Local reactions include swelling, fever, irritability, and crying spells. Severe reactions include encephalopathy, paralysis, and even death. The expected rate of severe reactions ranges between one in 100,000 and one in 310,000 doses. Prior to this incident, there had been only one case of transverse myelitis reported in connection with a DPT vaccine.

During the 1950's, the Eli Lilly Company developed a fractionated cell pertussis vaccine called Tri-Solgen that was prepared by treating whole killed pertussis cells with salt. Early studies indicated that this method of preparation resulted in a less toxic vaccine, and following its approval by the FDA in 1967, Tri-Solgen occupied a substantial share of the market. Lilly withdrew from the vaccine business in 1975 and stopped producing Tri-Solgen. Lilly sold the right to produce Tri-Solgen to Wyeth Laboratories; however, the FDA has refused to relicense the vaccine.

Lederle was aware of the neurotoxicity of Tri-Immunol as early as the 1950's and since that time has received occasional reports of severe adverse reactions to the vaccine. Following FDA approval of Tri-Solgen, Lederle conducted an internal study comparing Tri-Immunol with Tri-Solgen in an effort to determine whether to develop its own fractionated cell product. The study found fewer local reactions associated with Tri-Solgen, but it noted no severe reactions in either cohort due to the restricted number of subjects studied. At trial, Dr. Frank Cano, the Manager of Biologics at Lederle, testified that the differences observed in the study lacked statistical significance. Lederle only experimented with the production of a fractionated cell product until 1975. Since then, Japan has developed a pertussis toxoid vaccine, and Lederle's research efforts to achieve that objective may reach fruition within the next few years.

The principal thrust of appellees' negligence argument at trial concerned Lederle's failure to develop a fractionated cell product. In support of this theory, appellees contend that Tri-Solgen was shown to be a safe yet equally efficacious pertussis vaccine. Appellees' experts testified that the whole cell vaccine was five times more reactive than the fractionated cell product, and that early studies indicated that Tri-Solgen caused fewer local reactions than the whole cell vaccine. The studies did not establish, however, that Tri-Solgen caused fewer severe reactions than the whole cell vaccine. With regard to efficacy, appellees produced four studies that found that fractionated cell products produced an immune response to pertussis. However, in 1972, a review panel within the Bureau of Biologics of the FDA refused to certify Tri-Solgen as "safe and effective" although it did so certify the whole cell vaccines. Because the FDA has refused to relicense Tri-Solgen or any other fractionated cell product, the manufacture and sale of such a vaccine by Lederle, or any other pharmaceutical company, would constitute a criminal offense under the Food, Drug and Cosmetic Act. See 21 U.S.C. §§ 331(d), 333(a), 355(a) (1982). Toner v. Lederle Laboratories, 779 F.2d 1429, 1430-31 (9th Cir. 1986) (footnotes added).

As noted, Toner vigorously disputes this characterization of the facts. Without the trial record (other than the proposed and given jury instructions) before us, we cannot make an independent assessment. However, until it is determined otherwise, we must presume that sufficient evidence supported the jury's verdict that Lederle was negligent. See Glovatorium, v. N.C.R. Corp., 684 F.2d 658, 660 (9th Cir. 1982) ("This court will not disturb a jury verdict unless the evidence is such `that no reasonable [person] would accept it as adequate to establish the existence of each fact essential to the liability.' Kunz v. Utah Power Light Co., 526 F.2d 500, 504 (9th Cir. 1975). . . . ").

By examining the allegations, the jury instructions, and the jury verdicts, we can further narrow that which we must presume. Lederle's standard of care relevant to the allegations of negligence was most specifically addressed in the following jury instruction, requested by Lederle and given by the trial court:

INSTRUCTION NO. 27: A manufacturer of vaccines has the duty to exercise ordinary and reasonable care not to expose the potential consumer to an unreasonable risk of harm from the use of its products. The failure to meet this standard of due care in light of all the attendant circumstances will constitute negligence and subject the manufacturer to liability for the resulting consequences. The fact that the consumer's injuries were proximately caused by the manufacturer's product does not in and of itself constitute a sufficient basis upon which to predicate the manufacturer's liability. When the cause of action sounds in negligence, a manufacturer's duty to additionally test and investigate the propensities of its product is dependent upon the foreseeable risk of harm to potential users in light of then current scientific or medical knowledge and discoveries. R., Vol. II, p. 90, quoted in Toner, supra, 779 F.2d at 1431-32.

Toner specifically alleged "[t]hat Lederle was negligent in manufacturing and/or marketing the vaccine." R., Vol. 2, p. 85 (Jury Instruction No. 18). As we understand it, the thrust of Toner's case was not that the whole cell vaccine itself could have been more safely designed, but that Lederle knew of a safer alternative design — the fractionated cell vaccine — but failed to develop it and seek FDA certification of it. Toner alleged that Lederle could have marketed the safer alternative, but negligently failed to do so.

The jury returned the following verdict:

QUESTION NO. 2: Was defendant Lederle Laboratories negligent in connection with the product Tri-Immunol which was the proximate cause of the plaintiff's injuries? Yes. Toner, supra, 779 F.2d at 1433.

Taking the jury instructions, the allegations, and the jury verdict together, we conclude the jury found that "in light of all the attendant circumstances," Lederle failed "to exercise ordinary and reasonable care not to expose the potential consumer to an unreasonable risk of harm from the use of its products," R., Vol. 2, p. 90 (Jury Instruction No. 27), that "the foreseeable risk of harm to potential users in light of then current scientific or medical knowledge and discoveries" was such that Lederle was negligent in failing to further "test and investigate the propensities of its product" relative to those of the allegedly safer product, id., and that as a result Lederle was negligent for having "manufactur[ed] and/or market[ed] the [whole cell] vaccine" rather than the alternative. R., Vol. 2, p. 85 (Jury Instruction No. 18).

Certain factual presumptions also flow from the instructions, allegations, and verdict on the strict liability claim. The jury was instructed as follows:

INSTRUCTION NO. 21: A product is in a defective condition, unreasonably dangerous to persons if it is more dangerous than would be expected by an ordinary person who may reasonably be expected to use it. The law does not say what would be expected by an ordinary person or who may reasonably be expected to use the product. Both of these issues are for you to decide. R., Vol. 2, p. 87.

The jury received no instruction based on comment k of Restatement (Second) of Torts § 402A (1965).

Toner alleged "[t]hat at the time the vaccine was manufactured it was defective, in that it subjected the users to an unnecessary risk of serious harm or death." R., Vol. 2, p. 85 (Jury Instruction No. 18). However, the jury returned the following verdict:

QUESTION NO. 3: Was the product Tri-Immunol manufactured by the defendant Lederle Laboratories in a defective condition unreasonably dangerous to persons which was the proximate cause of the plaintiff's injuries? No. Toner, supra, 779 F.2d at 1433.

Taking the instructions, arguments, and verdict together, we conclude that the jury found the vaccine not to be "in a defective condition unreasonably dangerous to persons. . . ." Id. Nothing in the record before us indicates that either the jury or the trial court made any determination based on comment k.

We undertook the above exercise in order to understand the jury's determinations in relation to the certified questions, and to put our answers to those questions in perspective. As will become clear, the posture of this case dictates the extent of detail of our answers.

II. THE CERTIFIED QUESTIONS

The Court of Appeals posed the two questions which we accepted as follows:

(1) Under Idaho law, do the principles set forth in Restatement (Second) of Torts § 402A comment k apply to strict liability and negligence claims, and in particular to the claims in this suit? . . . .

(4) Were the jury instructions on the issue of negligence in full accordance with Idaho law, given the contentions of the parties in this case? Toner, supra, 779 F.2d at 1433.

However, the Court of Appeals invited us to "reformulate the relevant state law questions as [we] perceive them to be. . . ." Id. Upon consideration, we find such reformulation necessary.

The first certified question in reality is two: do the principles of comment k apply to strict liability claims, and do they apply to negligence claims. We will address the first part of the first question separately.

The second question (numbered (4) above) appears to directly relate to the latter part of the first question, particularly in light of the Court of Appeals' following discussion:

Appellant argues that the instruction [No. 27, quoted supra] is insufficient because it does not recognize that certain drugs have unavoidable risks but must, nevertheless, be used to protect the public health. To support its argument, appellant cites Restatement (Second) of Torts § 402A comment k (1965), which recognizes that the marketing of some drugs is fully justified to prevent disease despite risks inherent in their use. As appellant recognizes, the Restatement section and its comment pertain to strict liability; but, appellant argues, the controlling principles are also applicable to the question of liability for negligence.

Though appellees contend that the issue in this case is not the applicability of comment k but, rather, the appellant's alleged negligence in failing to develop a fractionated cell vaccine, we see the questions as related. The concept of an unavoidably unsafe product seems necessarily to depend on whether research was properly pursued. If this is true, the trial court may have omitted a material element of negligence in failing to instruct the jury to decide whether Tri-Immunol was an unavoidably unsafe product. Id. at 1432.

The negligence instructions would seem to present no difficulties to the Court of Appeals, except in relation to Lederle's argument concerning comment k. The Court of Appeals apparently wishes this Court to determine both (1) whether the principles of comment k apply to negligence claims, (as stated in the latter part of the first question), and if they do apply, (2) whether the above quoted negligence instruction (or any other of the given negligence instructions) sufficiently incorporates those principles.

Accordingly, we reformulate the certified questions as follows:

(1) Under Idaho law, do the principles set forth in Restatement (Second) of Torts § 402A comment k (1965) apply to strict liability claims, and in particular to the claim in this suit?

(2)(a) Under Idaho law, do the principles set forth in Restatement (Second) of Torts § 402A comment k (1965) apply to negligence claims, and in particular to the claim in this suit?

(b) If the above question no. (2)(a) is answered affirmatively, did the trial court's instructions on negligence sufficiently incorporate those principles?

III. QUESTION 1

We turn first to the question of whether the principles set forth in Restatement (Second) of Torts § 402A comment k apply to strict liability claims, and in particular to the claim in this suit. Our treatment of the question, however, will be general only. As best we can determine, the Court of Appeals poses the question for contextual purposes only. Nevertheless, we will examine comment k closely before venturing to adopt it or reject it.

Our belief that the Court of Appeals poses the question for contextual purposes only is based on our understanding that the issue the question involves is not before the court on appeal. Comment k provides an exception to strict liability for products deemed "unavoidably unsafe." Essentially, then, comment k is a defense to strict liability claims against products. In the instant case, the jury found the vaccine was not "in a defective condition unreasonably dangerous to persons which was the proximate cause of the plaintiff's injuries." Toner, supra, 779 F.2d at 1433 (quoting from the jury verdict). In other words, as the Court of Appeals noted, "the jury rejected the strict liability . . . claim. . . . Id. at 1430. The Toners do not appeal from that verdict. The viability of a defense to a claim, where the claim failed, and where the plaintiffs do not appeal, would not seem to be an issue on appeal.

The crux of Lederle's appeal involves whether the principles of comment k apply to a negligence claim — the claim upon which the jury found for the Toners. Comment k is a provision of Restatement (Second) of Torts § 402A (1965). Section 402A concerns claims based on the strict liability of sellers of products, and not claims based on negligence. The Court of Appeals may have thought it unlikely that this Court would apply the principles of comment k to a negligence claim without first determining that they apply to the strict liability claims for which the comment was designed. We will proceed with that understanding.

This Court adopted Restatement (Second) of Torts § 402A (1965) concerning the strict liability of sellers of products, of which comment k is a part, in Shields v. Morton Chemical Co., 95 Idaho 674, 676-77, 518 P.2d 857, 859-60 (1974). Subsequently, this Court has consistently adhered to § 402A and often to its accompanying comments. See, e.g., Rojas v. Lindsay Manufacturing Co., 108 Idaho 590, 592, 701 P.2d 210, 212 (1985) (applying comments i and l); Fish Breeders of Idaho, Inc. v. Rangen, Inc., 108 Idaho 379, 391 n. 3, 700 P.2d 1, 13 n. 3 (1985) (applying comments g, h, and j); Lasselle v. Special Products Co., 106 Idaho 170, 172, 677 P.2d 483, 485 (1984) (applying comment n); Farmer v. International Harvester Co., 97 Idaho 742, 747, 749, 553 P.2d 1306, 1311, 1313 (1976) (applying comment i); Mico Mobile Sales Leasing, Inc. v. Skyline Corp., 97 Idaho 408, 414, 546 P.2d 54, 60 (1975) (applying comment h); Rindlisbaker v. Wilson, 95 Idaho 752, 759-60, 519 P.2d 421, 428-29 (1974) (applying comments h and n). To date, a case implicating comment k has not presented itself.

In its entirety, comment k reads:

k. Unavoidably unsafe products. There are some products which, in the present state of human knowledge, are quite incapable of being made safe for their intended and ordinary use. These are especially common in the field of drugs. An outstanding example is the vaccine for the Pasteur treatment of rabies, which not uncommonly leads to very serious and damaging consequences when it is injected. Since the disease itself invariably leads to a dreadful death, both the marketing and the use of the vaccine are fully justified, notwithstanding the unavoidable high degree of risk which they involve. Such a product, properly prepared, and accompanied by proper directions and warning, is not defective, nor is it unreasonably dangerous. The same is true of many other drugs, vaccines, and the like, many of which for this very reason cannot legally be sold except to physicians, or under the prescription of a physician. It is also true in particular of many new or experimental drugs as to which, because of lack of time and opportunity for sufficient medical experience, there can be no assurance of safety, or perhaps even of purity of ingredients, but such experience as there is justifies the marketing and use of the drug notwithstanding a medically recognizable risk. The seller of such products, again with the qualification that they are properly prepared and marketed, and proper warning is given, where the situation calls for it, is not to be held to strict liability for unfortunate consequences attending their use, merely because he has undertaken to supply the public with an apparently useful and desirable product, attended with a known but apparently reasonable risk. (Emphasis original.)

Comment k establishes an exception to the test for strict product liability. That test as set out in § 402A imposes liability on "[o]ne who sells any product in a defective condition unreasonably dangerous to the user or consumer or to his [or her] property . . .," § 402A(1), whether or not "the seller has exercised all possible care in the preparation and sale of his product. . . ." § 402A(2)(a). Comment g defines "defective condition" as "a condition not contemplated by the ultimate consumer which will be unreasonably dangerous to him [or her]." Comment k, however, defines a category of "unavoidably unsafe" products which, "when properly prepared, and accompanied by proper directions and warning, [are] not defective, nor . . . unreasonably dangerous." (Emphasis original.) To leave no doubt, comment k restates the proposition: "The seller of such products, again with the qualification that they are properly prepared and marketed, and proper warning is given, where the situation calls for it, is not to be held to strict liability for unfortunate consequences attending their use. . . ." (Emphasis added.) Thus, if a product qualifies as "unavoidably unsafe," the seller is held not to the strict liability standard, but only to the standard of negligence.

As precondition to its application, comment k requires that the product be "properly prepared, and accompanied by proper directions and warning. . . ." Generally speaking, there are three varieties of product defects: manufacturing flaws, design defects, and inadequate warnings. Feldman v. Lederle Laboratories, 97 N.J. 429, 479 A.2d 374, 385 (1984). By its terms, comment k excepts unavoidably unsafe products from strict liability only where the plaintiff alleges a design defect, and not where the plaintiff alleges a manufacturing flaw or an inadequate warning. Comment k intends to shield from strict liability products which cannot be designed more safely; however, if such products are mismanufactured or unaccompanied by adequate warnings, then the seller may be liable even if the plaintiff cannot establish the seller's negligence. Courts and commentators universally agree to this limitation on comment k's grant of immunity from strict liability. See Brochu v. Ortho Pharmaceutical Corp., 642 F.2d 652, 657 (1st Cir. 1981); Reyes v. Wyeth Laboratories, 498 F.2d 1264, 1276 (5th Cir.), cert. denied, 419 U.S. 1096, 95 S.Ct. 1096, 42 L.Ed.2d 688 (1974); Davis v. Wyeth Laboratories, Inc., 399 F.2d 121, 128-29 (9th Cir. 1968); Yarrow v. Sterling Drug, Inc., 263 F. Supp. 159, 163 (Dist.S.D. 1967), aff'd, 408 F.2d 978 (8th Cir. 1969); Kearl v. Lederle Laboratories, 172 Cal.App.3d 812, 218 Cal.Rptr. 453, 465 ([Div. 4] 1985); Feldman, supra, 479 A.2d at 384; V. Schwartz, Unavoidably Unsafe Products: Clarifying the Meaning and Policy Behind Comment K, 42 Wn. Lee L.Rev. 1139, 1141 (1985); S. Willig, The Comment k Character: A Conceptual Barrier to Strict Liability, 29 Mercer L.Rev. 545, 546, 575 (1978).

Having met these preconditions, a seller next must establish that the product's risk is in fact "unavoidable." Comment k states: "There are some products which, in the present state of human knowledge, are quite incapable of being made safe for their intended and ordinary use." (Emphasis added.); see also, e.g., Belle Bonfils Memorial Blood Bank v. Hansen, 665 P.2d 118, 122 (Colo. 1983) ("[T]he risk must be unavoidable under the present state of knowledge."). Obviously, for this to be true, the design must be as safe as the best available testing and research permits. Schwartz, supra, 42 Wn. Lee L.Rev. at 1141.

As an additional element of an "unavoidable risk," there must be, at the time of the subject product's distribution, no feasible alternative design which on balance accomplishes the subject product's purpose with a lesser risk. See Kearl, supra, 218 Cal.Rptr. at 464; Belle Bonfils, supra, 665 P.2d at 123; Prosser and Keeton, The Law of Torts § 99, p. 700 (5th ed. 1984). If there were, then the risk would not be "unavoidable" or "apparently reasonable." Nor would the "marketing and use of the [product] be fully justified" if there were such an alternative design. Consequently, comment k by definition would not apply. The evaluation of a purported alternative design and the subject product's design should consider the magnitude of the subject product's risk that the alternative avoids, the financial costs of the compared designs, the benefits of the compared designs, and the relative safety of the compared designs, including any new risk that the alternative would pose. See Kearl, supra, 218 Cal.Rptr. at 464, Belle Bonfils, supra, 665 P.2d at 123; Prosser and Keeton, supra, § 99, p. 700.

Where their risks are unavoidable, comment k shields from strict liability those sellers who "supply the public with an apparently useful and desirable product, attended with a known but apparently reasonable risk." As examples of such products the comment cites (1) the Pasteur treatment of rabies, which averts "a dreadful death" while "not uncommonly lead[ing] to very serious and damaging consequences when it is injected," and (2) "new or experimental drugs as to which, because of lack of time and opportunity for sufficient medical experience, there can be no assurance of safety, or perhaps even of purity of ingredients, but such experience as there is justifies the marketing and use of the drug notwithstanding a medically recognizable risk." Clearly, the comment contemplates a weighing of the benefit of the product against its risk. Obviously, for comment k to apply, the benefit must outweigh the risk. This weighing process should consider the value of the benefit, the seriousness of the risk, and the likelihood of both. Belle Bonfils, supra, 665 P.2d at 122; Kearle, supra, 718 Cal.Rptr. at 464. We agree with Professor Sidney Willig that "[i]t does not serve society that an unavoidably unsafe product, which has occasional or fractious benefit, should enjoy insulation from strict liability in tort when the product's predominant effects are detrimental to individual and public safety." Willig, supra, 29 Mercer L.Rev. at 545. Consequently, the scales must clearly tip in favor of the benefits for comment k to apply. Cf. Brochu, supra, 642 F.2d at 657 ("If, as Comment k explains, the danger is unavoidable and the utility is great, liability may be avoided with proper warning." (Footnote omitted.)); Belle Bonfils, supra, 665 P.2d at 122 ("The product's utility must greatly outweigh the risk created by its use. . . ."); Kearl, supra, 218 Cal.Rptr. at 464 ("If the court concludes after taking such evidence that (1) the product was intended to provide an exceptionally important benefit that made its availability highly desirable, (2) the risk posed by the product was substantial and unavoidable when distributed, and (3) the interest in availability, measured as of the time of distribution, outweighs the interest in promoting enhanced accountability, the product will be deemed unavoidably dangerous and exempted from strict products liability design defect analysis.")

The weighing must be done as of the time the product is distributed to the plaintiff. Belle Bonfils, supra, 665 P.2d at 122-23; Kearl, supra, 218 Cal.Rptr. at 464; Cochran v. Brooke, 243 Or. 89, 409 P.2d 904, 906 (1966). Comment k does not require sellers to be clairvoyant. When, a product is " apparently useful and desirable," (emphasis added), considering its benefits and risks, then it ought to be immune from strict liability. Such products can include new or experimental drugs for which "there can be no assurance of safety." Comment k only requires that the balance " apparently" tip toward the benefit of a product at the time of distribution. Accord, Schwartz, supra, 42 Wn. Lee L.Rev. at 1144. No strict liability attaches if, contrary to the best available information, the risk later proves greater. in this manner, comment k removes a disincentive to "the development of new drugs that have the potential for conquering disease." Id. (emphasis original).

It follows that when the balance appears at the time of distribution to tip toward the benefit of a product, strict liability will not attach when an unexpected and unknown risk injures a user. Id. (see cases cited therein); see also Singer v. Sterling Drug, Inc., 461 F.2d 288, 290 (7th Cir.), cert. denied, 409 U.S. 878, 93 S.Ct. 131, 34 L.Ed.2d 132 (1972); 3 L. Frumer and M. Friedman, Products Liability § 33.02[4] (1983). Taken out of context, comment k's reference to a "known but apparently reasonable risk" can be read to extend its coverage to only known risks. See Belle Bonfils, supra, 665 P.2d at 123. However, by specifically including new and experimental drugs for which "there can be no assurance of safety," and other products whose benefits appear to outweigh their risks at the time of distribution, comment k clearly intends to guard against strict liability resulting from unknown risks as well as known risks. When comment k then refers to "a known but apparently reasonable risk," it refers not to specific side-effects or other hazards known at the time of distribution, but rather to what is known to be the over-all risk of the product, perhaps including the possibility of unknown side-effects or other hazards in addition to those already known. Accord, Schwartz, supra, 42 Wn. Lee L.Rev. at 1144-45 (see cases cited therein); 3 Frumer and Friedman, supra, § 33.02[4]. Commentator Schwartz aptly observed:

[A]s a practical matter, there is little difference in the terms of actual harm between a risk that was "apparently reasonable" and turned out not to be (for example, risk of slight impairment of vision was known but blindness resulted) and a totally unknowable risk. To differentiate between the known risk that turns out to be more serious and a totally new risk, which may indeed be a minor risk, does not square with the policy underlying comment k or for that matter with common sense. The only reasonable conclusion is that comment k includes products which contain risks that were not knowable at the time of manufacture. Schwartz, supra, 42 Wn. Lee L.Rev. at 1145 (emphasis original).

While sellers need not be clairvoyant, they are held to the knowledge and experience of experts in their fields. Feldman, supra, 479 A.2d at 386-87; Belle Bonfils, supra, 665 P.2d at 126. Knowledge of the product's risks based on reliable and obtainable information is imputed to the seller. Id. Thus, the balancing between benefits and risks is based on the best available information at the time of distribution, not merely the information known to the seller.

Where the balancing results in the application of comment k's immunity from strict liability, the immunity is not perpetual. If new information later tips the balance toward the risk of a product, or if new developments make possible a safer design, at that point further distributions of the product are not protected by comment k. Says Schwartz: "The public policy of encouraging the production of new and hopefully efficacious drugs is not compromised by imposing a reasonable standard on manufacturers to be responsible for new developments and risks in drugs they have marketed." Schwartz, supra, 42 Wn. Lee L.Rev. at 1147.

Finally, the seller has the burden to establish the application of comment k. Belle Bonfils, supra, 665 P.2d at 122-23. Thus, comment k is an affirmative defense to a claim based on strict liability.

To summarize, comment k immunizes certain products from strict liability claims based on an alleged defective design, though not from strict liability claims based on alleged defective manufacture or inadequate warning. The products comment k shields cannot be designed to be more safe at the time of distribution, but bestow benefits which clearly appear at the time of distribution to outweigh their concomitant risks. This seems to us to be a sensible system. It also serves important policy considerations, particularly in the area of ethical drug manufacture. Commentator Schwartz puts it simply: "Society wishes to encourage the manufacture of ethical drugs, and the research and development of new drugs. The imposition of strict liability would stifle these goals." Schwartz, supra, 42 Wn. Lee L.Rev. at 1141. As the citations within our discussion above evince, comment k has been widely adopted. See also Restatement (Second) of Torts § 402A comment k Appendices; but see Collins v. Eli Lilly Co., 116 Wis.2d 166, 342 N.W.2d 37, 52 (1984) (Rejects comment k as "too restrictive and, therefore, not commensurate with strict products liability law in Wisconsin."). We hold that comment k applies to strict liability claims based on an alleged defective design of a product, where that product qualifies under the comment k test as set out above.

We do not believe comment k was intended to provide nor should it provide all ethical drugs with blanket immunity from strict liability design defect claims. The comment refers to "some" products which are unavoidably unsafe; the comment states such products are "especially common in the field of drugs;" the comment cites certain examples from that field deserving of its protection and notes that "[t]he same is true of many other drugs, vaccines, and the like . . . [and] of many new or experimental drugs. . . ." (Emphasis added.) Obviously, the comment does not apply to all drugs. Rather, the comment applies "when the situation calls for it," which is when the product is unavoidably unsafe, but is "an apparently useful and desirable product, attended with a known but apparently reasonable risk," or with an unknown risk which was not yet reasonably discoverable at the time of marketing. It is equally obvious that not all drugs are so perfectly designed that they cannot be made more pure or more safe, or that there are not safer, suitable alternatives; nor do the benefits of all drugs necessarily outweigh their risks. Brochu, supra, 642 F.2d at 655; Singer, supra, 461 F.2d at 290-91; Flood v. Wyeth Laboratories, Inc., 183 Cal.App.3d 1272, 228 Cal.Rptr. 700, 702-03 ([Div. 5] 1986); Kearl, supra, 218 Cal.Rptr. 463-64; Feldman, supra, 479 A.2d at 380, 383; Schwartz, supra, Wash. Lee L.Rev. at 1141.

In this case, as previously explained, we need not determine whether or not the vaccine at issue qualifies for comment k protection. In any event, it is not for a court sitting on appeal to make such a determination. The determination would require a full evidentiary hearing such as only a trial court can provide. Flood, supra, 228 Cal.Rptr. at 703 (involved DPT vaccine); Kearle, supra, 218 Cal.Rptr. at 463; Feldman, supra, 479 A.2d at 383-84. Like the Kearl court,

we are uncomfortable with the rather routine and mechanical fashion by which many appellate courts have concluded that certain products, particularly drugs, are entitled to such special treatment. Indeed, "[t]he statement that drugs are unavoidably [dangerous], and therefore within the protection of Comment k, has become almost tautological." (Comment, supra, 31 DePaul L.Rev. at 254.) 218 Cal.Rptr. at 463.

Courts must decide the applicability of comment k case-by-case, and only after taking evidence related to the various factors discussed above. Id. at 463-64; Feldman, supra, 479 A.2d at 383. Courts on appeal may review the finding below; "it is not [their] proper role, however, to assume or take judicial notice of facts sufficient to support such a finding." Kearl, supra, 218 Cal.Rptr. at 464.

IV. QUESTION NO. 2(a)

Question 2(a) asks: Under Idaho law, do the principles set forth in Restatement (Second) of Torts § 402A comment k (1965) apply to negligence claims, and in particular to the claim in this suit?

In a literal sense, comment k, when applicable, quite clearly does not act as a bar to negligence claims. By its own terms, the comment only bars claims that the product's design was "defective" and " unreasonably dangerous" (emphasis original) — in other words, strict liability claims. The comment expressly states that the seller of "unavoidably unsafe" products "is not to be held to strict liability for unfortunate consequences attending their use. . . ." The authorities universally agree that where a product is deemed unavoidably unsafe, the plaintiff is deprived of the advantage of a strict liability cause of action, but may proceed under a negligence cause of action. E.g., Johnson v. American Cyanamid Co., 239 Kan. 279, 718 P.2d 1318, 1319 (1986); Kearl, supra, 218 Cal.Rptr. at 465; Feldman, supra, 479 A.2d at 381; Stone v. Smith, Kline French Laboratories, 447 So.2d 1301, 1303 (Ala. 1984); Schwartz, supra, 42 Wn. Lee L.Rev. at 1139-41; 3 Frumer and Friedman, supra, § 33.02[4], p. 328; Prosser, supra, § 99, p. 661.

By denying plaintiffs recovery based on the dangerousness of the product and requiring plaintiffs to prove negligent conduct on the part of the defendants, comment k furthers the policy of encouraging the production and marketing of useful products. Schwartz, supra, 42 Wn. Lee L.Rev. at 1144. However, to immunize sellers of products deemed unavoidably unsafe pursuant to comment k from negligence claims would remove needed incentive for safe design. Id. at 1141; 3 Frumer and Friedman, supra, § 33.02[4], p. 328.2. In the process of arguing that comment k covers unknown as well as known risks, Schwartz illustrates the balance comment k achieves between encouraging development and promoting safety — a balance which would topple were there no action in negligence:

Applying comment k to drugs that contain risks that were unknown at the time of manufacture simply keeps these drugs within the ambit of negligence law. Under negligence law, the pharmaceutical company is held to the very highest of standards. The pharmaceutical company must act as a reasonable person would have acted in the same or similar circumstances. The circumstances in which pharmaceutical manufacturers must deal directly involve severe risks to human life. Thus, their standard of care is not the "reasonableness" of a person who repairs a television set or drives a car — it is the most serious and intense obligation that one can find in the entire body of negligence law. To go beyond this, and require manufacturers to be responsible for the unknown (that is, to impose absolute or strict liability), flies in the face of Sce overall policy underlying the section. Schwartz, supra, 42 Wn. Lee L.Rev. at 1144-45 (emphasis original) (footnotes omitted).

Professor Willig aptly concludes:

If plaintiff cannot adduce evidence to prove that the product was defective, improperly prepared or unaccompanied by proper direction and warning, § 402A should not be available; but unlikely as it might sound, plaintiff should not be precluded in essaying a cause of action in negligence. Willig, supra, 29 Mercer L.Rev. at 546 (footnote omitted).

Thus, when comment k applies, the plaintiff still may allege negligence. Further, even if the application of comment k is a question for the judge ( see supra, n. 7), the determination of negligence remains for the jury.

In a general sense, however, the comment k concerns and its required balancing between risks and benefits are similar to those involved in a negligence claim. As the Restatement notes, for an act to be unreasonable and thus a breach of duty under negligence analysis, the risk must be "of such magnitude as to outweigh what the law regards as the utility of the act or of the particular manner in which it is done." Restatement (Second) or Torts § 291 (1965); see also Brizendine v. Nampa-Meridian Irrigation Dist., 97 Idaho 580, 586, 548 P.2d 80, 86 (1976) ("`[I]n negligence cases, the duty is always the same, to conform to the legal standard of reasonable conduct in the light of the apparent risk.'" Quoting Prosser, supra, § 53, p. 324); United States v. Carroll Towing Co., 159 F.2d 169, 173 (2d Cir. 1947). Comment k requires a similar weighing. Under negligence analysis, the utility of the act depends upon the value of the interest advanced, the extent to which it is advanced, and the opportunity for a less dangerous course of conduct, Restatement (Second) of Torts § 292 (1965), just as comment k's application depends on the value of the product's benefit, the extent to which the benefit accrues, and the availability of a feasible alternative design. The risks too are similarly considered by comment k and negligence law. See Restatement (Second) of Torts § 293 (1965). Such a weighing is implicit in the duty to use due care to avoid injuries while rendering services. Stephens v. Stearns, 106 Idaho 249, 257, 678 P.2d 41, 49 (1984). In sum, the determination under comment k that the design of a product is unavoidably unsafe and yet affords benefits outweighing its risks varies little from the determination under negligence law that the designing and marketing of the product was reasonably done. Cf. Feldman, supra, 479 A.2d at 385-86 ("`Since proper design is a matter of reasonable fitness, the strict liability adds little or nothing to negligence on the part of the manufacturer * * *.' W. Prosser, Law of Torts 659 n. 72 (4th ed. 1971)."); Willig, supra, 29 Mercer L.Rev. at 545 ("In terms of negligence liability, an unavoidably unsafe product with high benefit potential certainly may overcome an argument that its sponsor is derelict in duty, provided that its design or formulation, its instructions as to use, and its warnings as to dangers are reflective of the present state of human skill, knowledge and maker expertise."); Wade, supra, 44 Miss.L.J. at 841 ("There is little difference here [in cases of improper design] between the negligence action and the action for strict liability." (Footnote omitted.)).

We conclude that the principles of comment k do not literally apply to negligence claims. More specifically, comment k does not shield sellers of products from negligence claims. On the other hand, in a general sense, the principles of comment k relate to the negligence concepts as expressed in Restatement §§ 291-93. However, the question of negligence remains for the jury to decide.

V. QUESTION 2(b)

In answer to question 2(b), we hold that the jury instructions on negligence, particularly Jury Instruction No. 27, quoted supra, p. 6, adequately incorporated many though not all the principles common to comment k and negligence law as discussed above. Like comment k, Instruction No. 27 imposed on Lederle not the requirement of clairvoyance, but only the duty to act reasonably given "the foreseeable risk of harm to potential users in light of then current scientific or medical knowledge and discoveries." While the instruction did not explicitly establish a balancing between utility and risk, as we noted earlier, such a balancing is implicit in the instruction's requirement that the manufacturer "exercise ordinary and reasonable care not to expose the potential consumer to an unreasonable risk of harm from the use of its products." See Stephens, supra, 106 Idaho at 257, 678 P.2d at 49. Certainly the following admonition invited the jury to consider the benefits of the vaccine as well as its risks: "The failure to meet this standard of due care [not to expose the potential consumer to an unreasonable risk of harm] in the light of all the attendant circumstances will constitute negligence. . . ." R., Vol. II, p. 90 (Jury Instruction No. 27) (emphasis added). Further, the instruction clearly indicated that the fact the vaccine caused Kevin's injury by itself did not justify a finding of negligence: "The fact that the consumer's injuries were proximately caused by the manufacturer's product does not in and of itself constitute a sufficient basis upon which to predicate the manufacturer's liability." Id. Thus instructed, the jury undoubtedly considered the state of scientific knowledge and the utility of the vaccine before assigning negligence. Apparently, the jury was convinced that Lederle was negligent for having manufactured and marketed the whole cell vaccine instead of a safer alternative. However, the negligence principles common to comment k and Restatement (Second) of Torts §§ 291-93 (1965) could have been stated more explicitly. Had Lederle requested an instruction based on Restatement (Second) of Torts §§ 291-93, such an instruction would have accurately reflected Idaho law.

VI. CONCLUSION

We have answered the certified questions in accordance with Idaho law and with well established precepts of strict liability and negligence law. Our answers in part may disappoint Lederle and amicus Pharmaceutical Manufacturers Association. Both sought total immunity from both strict liability and negligence claims for sellers of drugs so long as those drugs satisfied the requirements of the FDA and comment k. Their arguments were based less on legal authority than on policy considerations. Even without the record before us, we are aware of society's critical need for the DPT vaccine. No doubt liability flowing from the occasional injuries inflicted by the vaccine acts as a disincentive to its manufacture. However, this Court is not equipped to decide as a matter of public health policy that the relative efficacy and safety of the whole cell vaccine is so well established and the plight of Lederle so dire that injured persons such as Kevin Toner should be denied any recourse. Faced with similar supplications, the California Court of Appeals, Second District, Division 5, observed:

Wyeth is not alone in predicting that a DPT vaccine shortage will be caused by the suits brought against the manufacturers, because production will become unprofitable. (See Horn, Vaccine Crisis Spurs Bills in Congress (Summer 1985) 10 Litigation News 5.) If this should occur, we would expect the Legislature to intervene to prevent the resulting health crisis. This is a legislative function. Flood, supra, 228 Cal.Rptr. at 703.

The Flood court's expectation was not unrealistic. At the time of this writing, the United States Congress has passed and the President has signed a bill "that would establish a federal `no fault' compensation program for children injured as a result of routine, required vaccinations. . . ." The Idaho Statesman, October 15, 1986. This approach radically revises tort law in order to simultaneously protect the interests of society, the drug industry, and innocent victims of the rare but catastrophic severe reactions. It is an approach quite within the capacity of the legislative branch of government, but quite beyond the capacity of the judicial branch.

Remanded to the Court of Appeals.

DONALDSON and HUNTLEY, JJ., concur.