If the U.S. Supreme Court sides with the petitioners in Bruesewitz v. Wyeth, the ruling could undermine the National Childhood Vaccine Injury Act of 1986 and drag the field back decades to a time when litigation stifled vaccine R&D. Central to the case is an ambiguous clause in the Act that prevents patients from taking vaccine manufacturers to state civil courts for injuries allegedly caused by a vaccine's defective design.

Because the clause isn't crystal clear, the justices likely will need to consider documents from the time of the Vaccine Act's enactment to determine whether Congress intended the law to give vaccine manufacturers immunity to all design-defect claims, or only some of them. Unfortunately, the congressional record is also murky.