“Exclusive-Causation” under the Vaccine Act: A Commentary on Amanda Watts v. Maryland CVS Pharmacy, LLC

1. Introduction

In Amanda Watts v. Maryland CVS Pharmacy, LLC, the United States Court of Appeals for the Fourth Circuit confronted a factual scenario that pits state tort doctrines against the broad immunity conferred by the federal National Childhood Vaccine Injury Act of 1986 (“Vaccine Act”). Ms. Watts alleged negligent injection of two vaccines—Boostrix (a Vaccine-Act–covered vaccine) and Pneumovax 23 (not covered)—administered sequentially and in the same location on her arm. After developing Complex Regional Pain Syndrome (“CRPS”), she sued CVS, but purposely limited her complaint to Pneumovax, hoping to bypass CVS’s statutory immunity for Boostrix.

The central issue: Can a plaintiff recover on a state-law negligence claim when her experts cannot isolate the injury to the non-covered vaccine and the covered vaccine is shielded by federal immunity? The Fourth Circuit answered “No,” effectively creating what this commentary calls the “exclusive-causation” requirement: when Vaccine Act immunity applies to one of multiple potential causes, a plaintiff must produce evidence that the actionable (non-covered) vaccine independently caused the alleged injury.

2. Summary of the Judgment

The district court struck a post-deposition errata sheet by plaintiff’s causation expert (Dr. Chhatre) that attempted to shift from an “either/or” to a “both contributed” theory.
Without that errata—and even assuming it remained—the court granted summary judgment because Watts offered no expert testimony isolating Pneumovax as the cause of her CRPS.
The Fourth Circuit affirmed, holding that:
1. CVS’s Vaccine Act immunity for Boostrix barred any claim premised in whole or in part on Boostrix.
2. Maryland doctrines such as substantial factor or alternative liability cannot override federal immunity.
3. Absent evidence that Pneumovax alone caused the injury, a jury would be left to “guess,” defeating the causation element of negligence.

3. Analysis

3.1 Precedents Cited

The panel referenced three main groups of authority:

Federal Vaccine Act & VIC Program (42 U.S.C. § 300aa-10 et seq.) – establishes exclusive remedy and immunity for covered vaccines (here, Boostrix).
Maryland State Tort Doctrines – Mayer v. North Arundel Hospital Ass’n, 802 A.2d 483 (Md. Ct. Spec. App. 2002) (substantial factor/indivisible injury) and Thodos v. Bland, 542 A.2d 1307 (Md. Ct. Spec. App. 1988) (alternative liability).
Federal Civil Procedure – Rule 30(e) (scope of post-deposition changes).

Although the Maryland decisions normally enable plaintiffs to recover the full extent of an indivisible injury from any negligent defendant, the Fourth Circuit emphasized that federal immunity displaced those doctrines where a covered vaccine was involved.

3.2 Legal Reasoning

Statutory Immunity Supremacy
The Vaccine Act’s exhaustion requirement bars litigation “for damages arising from a vaccine-related injury” unless the claimant first proceeds through the VIC Program when the vaccine is covered. Boostrix is covered; Pneumovax is not. The statutory structure immunizes CVS from any lawsuit “for damages arising from” Boostrix. Therefore, any state-law causation theory that even partly depends on Boostrix collides with federal law and fails.
Causation Burden Restated
Because CVS’s potential liability could arise only from Pneumovax, Watts must prove by a preponderance of the evidence that Pneumovax caused her CRPS. Expert evidence equivocal on causation is insufficient; the court characterized it as asking a jury to “guess.”
Rule 30(e) and Expert Errata
The district court (adopted implicitly by the Fourth Circuit) followed the majority view that Rule 30(e) permits corrections or clarifications, not wholesale substantive reversals. Dr. Chhatre’s add-on sentence converted an “either/or” to “both” theory—too material to be a mere correction, and therefore struck. Even if considered, it would still run aground on immunity.
Inapplicability of Maryland Joint-Tortfeasor Doctrines
The court distinguished Mayer and Thodos. Both allow recovery when multiple tortfeasors jointly cause an indivisible injury or where it is unclear which one caused it. But applying either would necessarily impose liability on CVS for injury partly produced by Boostrix—expressly prohibited by the Vaccine Act.

3.3 Impact of the Decision

The ruling cements an “exclusive-causation” threshold for any suit involving a covered and a non-covered vaccine administered together:

Plaintiffs must segregate causation evidence to the non-covered vaccine; otherwise, claims will be dismissed at summary judgment.
Traditional state-law doctrines of indivisible injury and alternative liability are pre-empted to the extent they would impose liability arising from a covered vaccine.
Healthcare providers gain increased predictability: if they administer a mix of covered and non-covered vaccines, immunity for the covered one cannot be circumvented through broad pleading.
Practically, claimants may be forced to use the VIC Program—even for injuries they believe stem partly from a non-covered vaccine—because proof may not be disentangled.
Future litigation will likely focus on:
- Expert methodologies capable of pinpointing which injection caused the injury (e.g., imaging, spatial pain mapping, distinct markers).
- The boundaries of Rule 30(e) modifications in expert testimony within the Fourth Circuit (an issue still formally unresolved).

4. Complex Concepts Simplified

4.1 Vaccine Act Immunity

The Vaccine Act creates a “no-fault” compensation system—the VIC Program—so vaccine manufacturers and administrators are insulated from most lawsuits. If a vaccine appears on the “Table” (Boostrix does), a person injured must first submit a petition to the Court of Federal Claims. If they skip this step, all civil claims over that vaccine are barred.

4.2 Indivisible Injury & Substantial Factor

When multiple negligent acts combine to produce harm that cannot be apportioned, many states let the plaintiff sue any one defendant for the entire loss (indivisible injury), provided that defendant’s conduct was a “substantial factor” in causing the harm. The Fourth Circuit here says federal immunity blocks that state-law shortcut when one of the factors (Boostrix administration) is un-suable.

4.3 Alternative Liability

Sometimes two negligent actors both could have caused the injury, and it is impossible to determine which one did. Under alternative liability, the burden shifts to defendants to absolve themselves. The doctrine again fails where federal law immunizes one potential actor.

4.4 Rule 30(e) “Errata” Sheets

Federal Rule of Civil Procedure 30(e) lets a deponent review and correct deposition transcripts within 30 days. Courts widely distinguish:

Clarifications/Corrections – permissible (e.g., fixing a date, a misstatement).
Material Contradictions – usually impermissible if they attempt to “create” an issue of fact that did not exist.

The Fourth Circuit has not yet published a definitive standard, but Watts follows district precedent that bars substantive reversals.

5. Conclusion

Amanda Watts v. Maryland CVS Pharmacy, LLC establishes that when a covered and a non-covered vaccine are injected contemporaneously, a plaintiff must prove—through exclusive-causation evidence—that the actionable, non-covered vaccine caused her injuries. The decision reinforces federal supremacy where statutory immunity collides with state-law theories of joint or alternative liability. It also signals to plaintiffs and experts alike: causation cannot be blended when the Vaccine Act is in play. In the broader legal landscape, Watts tightens the causal-proof requirements for vaccine-related negligence suits and underscores the protective perimeter Congress created around covered vaccines.