Here at the DDL Blog, we love phrases denoting that two things are acting together or in close succession to produce a result. We have written more than once on the “one-two punch” of causation and implied preemption, and who doesn’t appreciate a good “double whammy” in whatever context? Cases with different outcomes are often the “yin” and the “yang” of the law, and we like it when defendants have the plaintiffs caught “between a rock and a hard place.” And don’t forget the narrow gap between express and implied preemption.
Yes, noteworthy things often come in pairs. But what do you call it when a patient gets two vaccines on the same day and only one is entitled to statutory immunity, but no one knows which vaccine came first or whether one or the other caused the patient’s alleged injury? You might call it a double fault, or strike two, or any other clever phrase you can come up with.
The Fourth Circuit called it “summary judgment.” In Watts v. Maryland CVS Pharmacy, LLC, No. 23-2025, 2025 WL 1802385 (4th Cir. July 1, 2025) (to be published in F.4th), the plaintiff received two vaccines during the same visit in the same spot on her arm, but only one vaccine was subject to immunity under the National Childhood Vaccine Act. Lo and behold, when the plaintiff sued for alleged injuries, she sought to hold the provider liable only for the non-immune vaccine. She didn’t even mention the other vaccine in her complaint.
That was a big mistake. The plaintiffs’ expert reports made no mention of the other vaccine, and her causation expert attributed her injuries only to the one mentioned in the complaint. It got awkward when both experts had to admit in their depositions that they had not known about the other vaccine when they wrote their reports and that although one vaccine or the other caused the plaintiff’s injuries, they could not say which one. Id. at *2-*3.
It got even more awkward when the causation expert served a “Notice of Errata” a month after his deposition purporting to add a sentence to his report stating that both vaccines caused the injury. Id. at *3.
That was out of bounds. The rules allow an errata to correct misstatements or clarify existing answers, not to “materially change the answers or fully supplant them.” This expert’s errata crossed the line. He previously stated in report that he had “considered other potential causes” and that the one vaccine had caused the harm, but he now was attributing the plaintiff’s injuries to both vaccines. The light is red, not green. (For more on errata abuse see our post on the topic here.)
On the merits, the parties debated “substantial factor” causation and “alternate liability” under Maryland law (remember the two hunters in Summers v. Tice from law school?). But this case was governed by federal law—the Vaccine Act, under which the defendant was immune unless the plaintiff could prove that her injuries were caused by the non-immune vaccine and not the other. That was a problem for the plaintiff because both her experts said that one vaccine caused her injuries, but neither could say which one. Without evidence on which vaccine (if any) caused the harm, “a jury could do no more than ‘guess’ as to that crucial element.” Id. at *4.
Still further, even if the causation expert had been permitted to opine that both vaccines caused the harm, the defendant would still be entitled to summary judgment. That is because the plaintiff would then be relying for liability upon the immunized vaccine “as a second, separate negligent act,” which the Vaccine Act bars. This plaintiff alleged one set of indivisible injuries, and it was not possible to apportion the harm to one vaccine or the other. The plaintiff certainly presented no evidence that would allow any jury to make that call.
Plaintiff could have pursued claims under the National Vaccine Injury Compensation Program, but she chose not to, and now she is stuck. Perhaps she was trying to kill two birds with one stone, or maybe dance a two-step through the litigation lottery. For our two cents worth, this is the correct outcome.