WET Exemptions: Why Most Manufacturers Get This Wrong

Written by HATEM RABEH, MD, MSc Ing

Your Clinical Evaluation Expert And Partner

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Well Established Technology under MDR Annex XIV offers a narrow path to reduced clinical investigation requirements. But the exemption is surrounded by conditions that most manufacturers underestimate.

The misconception is simple: many believe WET is about device age or market presence. It is not. WET is about technology characteristics, safety data, and the absence of certain risks. Miss one criterion, and the exemption collapses.

This is not theoretical. I have seen multiple submissions fail because the manufacturer confused similarity with equivalence, or assumed their predicate device qualified without verifying the full chain of evidence.

What MDR Article 61(4) and Annex XIV Actually Say

MDR Article 61(4) permits manufacturers to avoid clinical investigations for certain Class IIa and IIb devices if they demonstrate the device relies on well-established technology.

Annex XIV, Section 1 defines the specific conditions. These are cumulative. All must be met.

The technology must be used in devices on the EU market for at least ten years. The safety and performance must be well established. There must be no significant changes to the intended purpose or technical and biological characteristics.

This last point is where most files break.

The Five Cumulative Criteria Manufacturers Overlook

Let me walk through the five conditions that Annex XIV establishes. Each one is a gate. If one fails, the entire WET claim fails.

1. The Technology Must Be Used in Similar Devices for at Least Ten Years

This is not about your device. This is about the underlying technology.

If your device uses a coating, a material, or a mechanism, you must show that this specific technology has been on the EU market for ten continuous years in devices with similar intended purpose and application.

The trap is assuming that any similar device counts. It does not. The technology trace must be specific, documented, and verifiable.

I reviewed a submission where the manufacturer cited ten-year market presence but referenced devices with different coatings. The Notified Body rejected it. The coating chemistry was different. The WET claim collapsed.

2. The Safety and Performance Must Be Well Established

This means literature, post-market data, and clinical evidence support the technology’s safety profile across the claimed ten years.

You cannot simply state that the technology is safe. You must demonstrate it with data.

This requires a literature review, analysis of vigilance data, field safety notices, and complaint trends. If the technology has shown recurring adverse events, even if manageable, WET may not apply.

The burden is on you to prove safety is well established. The Notified Body does not have to prove it is not.

3. No Significant Change to Intended Purpose

Even minor expansions in indication can disqualify WET status.

If your predicate device was indicated for diagnostic use and your device adds therapeutic claims, the intended purpose has changed. WET no longer applies.

The same holds for patient population. If the predicate was used in adults and you target pediatrics, the intended purpose has shifted.

I have seen manufacturers argue that the core function remains the same, so WET should still apply. The Notified Body disagreed. The shift in population introduced new risks. A clinical investigation was required.

4. No Significant Change to Technical Characteristics

This is where most manufacturers stumble.

You may believe your modification is minor. A different alloy. A revised surface finish. A slightly altered mechanism.

But if that change affects safety, performance, or biocompatibility, it is significant. And WET no longer applies.

The standard is not whether the change seems small to you. The standard is whether the change introduces new risks or alters the benefit-risk profile.

I worked with a manufacturer who changed the polymer in a catheter tip. The change improved flexibility. But it also altered thrombogenicity. The Notified Body rejected WET. A clinical study was required.

5. No Significant Change to Biological Characteristics

This is closely tied to technical characteristics but focuses specifically on biocompatibility and biological interaction.

If your device has direct or indirect tissue contact and you modify the material, coating, or sterilization method, you may have changed the biological characteristics.

Even if your biocompatibility testing shows acceptable results, the change may still disqualify WET.

The reason is simple: long-term biological safety is what WET relies on. If you introduce a change, that long-term data no longer applies to your device.

Why Equivalence and WET Are Not the Same

This is a common confusion.

Manufacturers often believe that if they can claim equivalence under MDR Annex XIV, they automatically qualify for WET.

This is incorrect.

Equivalence is a broader concept. It allows you to leverage clinical data from another device if you can demonstrate technical, biological, and clinical similarity.

WET is narrower. It is a specific exemption from clinical investigations based on long-term established safety.

You can have equivalence without WET. You cannot have WET without equivalence.

But equivalence alone does not grant WET status. The ten-year technology trace and the absence of significant changes are additional gates.

I reviewed a file where the manufacturer demonstrated equivalence convincingly. But they could not trace the technology back ten years. The predicate device had only been on the market for six years. WET was denied.

The Documentation You Must Prepare

If you want to claim WET, your technical documentation must include specific elements.

First, a detailed technology description. Not the device. The technology. Materials, mechanisms, design principles, and biological interaction.

Second, a market presence timeline. Show which devices used this technology over the past ten years. Provide regulatory clearances, marketing authorizations, and commercialization evidence.

Third, a safety data compilation. Literature review, post-market surveillance summaries, vigilance data, complaint trends, and field actions.

Fourth, a change analysis. Compare your device to the predicate devices. Identify every difference. Justify why each difference is not significant.

This last step is where most files fail. Manufacturers list differences but do not explain why they are not significant. The Notified Body interprets absence of justification as inability to justify.

What Happens When WET Is Challenged

If the Notified Body questions your WET claim, you have limited options.

You can provide additional evidence. Expand the literature review. Add post-market data. Clarify the technology trace.

But if the Notified Body concludes that one or more criteria are not met, you must conduct a clinical investigation.

This is not negotiable.

I have seen manufacturers try to argue that the risk is low, so WET should still apply. The regulation does not work that way. WET is a privilege, not a default. If the criteria are not met, the privilege is withdrawn.

The consequence is delay. You must design a clinical study, gain ethics approval, recruit patients, collect data, and submit results. This can add twelve to twenty-four months to your timeline.

Plan for this possibility. Do not assume WET will hold if your evidence is marginal.

How Notified Bodies Evaluate WET Claims

Notified Bodies approach WET claims with caution.

They know that WET is often stretched beyond its intended scope. So they scrutinize the evidence carefully.

They will check the ten-year timeline against public databases, clearance records, and market surveillance reports.

They will review your safety data compilation and compare it against known adverse events in EUDAMED, manufacturer field actions, and published case reports.

They will assess whether your change analysis is thorough. If you list a difference without justification, they will assume it is significant.

The threshold for rejection is lower than you might expect. If the reviewer has reasonable doubt, they will request a clinical investigation.

Your job is to eliminate that doubt before submission.

The Strategic Question You Should Ask Before Claiming WET

Before you invest time in a WET claim, ask this question: Can I trace this specific technology through ten years of market presence without ambiguity?

If the answer is yes, and if your device introduces no significant changes, WET may apply.

If the answer is no, or if you have doubt, do not build your regulatory strategy on WET.

Instead, prepare for a clinical investigation from the start. This avoids the risk of late-stage rejection and timeline disruption.

WET is not a loophole. It is a well-defined exemption with strict criteria. Treat it with the respect it requires.

I have worked with manufacturers who successfully claimed WET. They all had one thing in common: meticulous documentation, clear technology traceability, and honest assessment of their changes.

The manufacturers who failed had optimism without evidence.

WET rewards rigor. It punishes assumption.

Peace,
Hatem
Clinical Evaluation Expert for Medical Devices
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