(90 days)
WELLlife Flu A&B Home Test:
The WELLlife Flu A&B Home Test is a lateral flow immunochromatographic assay intended for the qualitative detection and differentiation of influenza A and influenza B nucleoprotein antigens directly in anterior nasal swab samples from individuals with signs and symptoms of respiratory tract infection. This test is for non-prescription home use by individuals aged 14 years or older testing themselves, or adults testing other individuals aged 2 years or older.
All negative results are presumptive and should be confirmed with an FDA-cleared molecular assay when determined to be appropriate by a healthcare provider. Negative results do not rule out infection with influenza or other pathogens. Individuals who test negative and experience continued or worsening respiratory symptoms, such as fever, cough and/or shortness of breath, should seek follow-up care from their healthcare provider.
Positive results do not rule out co-infection with other respiratory pathogens, and therefore do not substitute for a visit to a healthcare provider or appropriate follow-up.
WELLlife Influenza A&B Test:
The WELLlife Influenza A&B Test is a lateral flow immunochromatographic assay intended for the qualitative detection and differentiation of influenza A and influenza B nucleoprotein antigens directly in anterior nasal swab samples from individuals with signs and symptoms of respiratory tract infection. This test is for use by individuals aged 14 years or older testing themselves, or adults testing other individuals aged 2 years or older.
All negative results are presumptive and should be confirmed with an FDA-cleared molecular assay when determined to be appropriate by a healthcare provider. Negative results do not rule out infection with influenza or other pathogens. Individuals who test negative and experience continued or worsening respiratory symptoms, such as fever, cough and/or shortness of breath, should seek follow-up care from their healthcare providers.
Positive results do not rule out co-infection with other respiratory pathogens.
Test results should not be used as the sole basis for treatment or other patient management decisions.
The WELLlife Flu A&B Home Test and WELLlife Influenza A&B Test is a lateral flow immunochromatographic assay intended for the qualitative detection and differentiation of influenza A and influenza B protein antigens. The test has two versions, one for over the counter (OTC) use (WELLlife Flu A&B Home Test) and one for professional use (WELLlife Influenza A&B Test). Both versions of the WELLlife Influenza A&B Test that have an identical general design and are intended for the qualitative detection of protein antigens directly in anterior nasal swab specimens from individuals with respiratory signs and symptoms. Results are for the identification and differentiation of nucleoprotein antigen from influenza A virus, and nucleoprotein antigen from influenza B virus. The test cassette in the test kit is assembled with a test strip in a plastic housing that contains a nitrocellulose membrane with three lines: two test lines (Flu A line, Flu B line) and a control line (C line). The device is for in vitro diagnostic use only.
The provided FDA Clearance Letter for the WELLlife Flu A&B Home Test includes details on the device's performance based on non-clinical and clinical studies. Here's a breakdown of the acceptance criteria and the study proving the device meets them, based on the provided text:
Acceptance Criteria and Reported Device Performance
The acceptance criteria for performance are generally implicit in these types of submissions, aiming for high agreement with a comparative method. The reported performance is presented through Positive Percent Agreement (PPA) and Negative Percent Agreement (NPA).
Table 1: Acceptance Criteria and Reported Device Performance (Implicit Criteria)
| Metric | Acceptance Criteria (Implicit) | Reported Device Performance (Influenza A) | Reported Device Performance (Influenza B) |
|---|---|---|---|
| Clinical Performance (Agreement): | |||
| Positive Percent Agreement (PPA) | High agreement, typically >90% for acute infections [Implied] | 92.4% (95% CI: 87.2%-95.6%) | 91.4% (95% CI: 77.6%-97.0%) |
| Negative Percent Agreement (NPA) | Very high agreement, typically >98% [Implied] | 100% (95% CI: 99.3%-100%) | 100.0% (95% CI: 99.4%-100%) |
| Non-clinical Performance (Precision): | |||
| Lot-to-Lot Repeatability (1x LoD, positive) | 100% agreement over multiple lots, operators, and days [Implied] | 100% (180/180) | 100% (180/180) |
| Lot-to-Lot Repeatability (Negative) | 0% false positives [Implied] | 0% (0/180) | 0% (0/180) |
| Site-to-Site Reproducibility (1x LoD, positive) | Near 100% agreement across sites and operators [Implied] | 97.0% (131/135) | 99.3% (134/135) |
| Site-to-Site Reproducibility (Negative) | 0% false positives [Implied] | 0% (0/135) for Negative Sample | 0.7% (1/135) for Flu B High Negative (0.1x LoD) |
| Non-clinical Performance (Analytical Sensitivity): | |||
| Limit of Detection (LoD) | Specific concentrations where ≥95% detection is achieved | Ranges from $3.89 \times 10^0$ to $4.17 \times 10^2$ TCID50/mL for A strains | Ranges from $1.17 \times 10^1$ to $1.05 \times 10^3$ TCID50/mL for B strains |
| Non-clinical Performance (Analytical Specificity): | |||
| Cross-reactivity / Microbial Interference | No cross-reactivity or interference with listed organisms/viruses | 0/3 for all microorganisms/viruses tested | 0/3 for all microorganisms/viruses tested |
| Endogenous Interfering Substances | No interference with listed substances at specific concentrations | No interference with most substances, except FluMist Quadrivalent Live Intranasal Influenza Virus Vaccine (false positive at high concentrations) | No interference with most substances, except FluMist Quadrivalent Live Intranasal Influenza Virus Vaccine (false positive at high concentrations) |
| High Dose Hook Effect | No hook effect observed at high viral concentrations | 9/9 positive for Flu A strains | 9/9 positive for Flu B strains |
| Competitive Interference | Detection of low levels of one analyte in presence of high levels of another | 100% detection for all tested combinations | 100% detection for all tested combinations |
Study Details
1. A table of acceptance criteria and the reported device performance
- See Table 1 above. The acceptance criteria are inferred from what is typically expected for a diagnostic device of this type seeking FDA clearance (e.g., high sensitivity and specificity, consistent performance).
2. Sample size used for the test set and the data provenance (e.g. country of origin of the data, retrospective or prospective)
- Test Set Sample Size:
- Clinical Study: 680 evaluable subjects (from 766 enrolled) were used for clinical performance evaluation.
- Non-clinical Studies: Sample sizes vary by study:
- Lot-to-Lot Precision: 180 results per sample type (3 lots x 3 operators x 2 replicates x 2 runs per day x 5 days).
- Site-to-Site Reproducibility: 135 replicates per sample type (3 sites x 3 operators x 5 days).
- LoD: 20 replicates for confirmatory testing.
- Analytical Reactivity: Triplicates for initial range finding, then triplicates for two-fold dilutions.
- Cross-Reactivity/Microbial Interference: 3 replicates per organism/virus.
- Endogenous Interfering Substances: 3 replicates per substance.
- High Dose Hook Effect: 9 replicates (across 3 lots).
- Competitive Interference: 9 replicates for each combination.
- Data Provenance:
- Clinical Study: "A prospective study was performed... between January 2025 and March 2025... at six (6) clinical sites." The country of origin is not explicitly stated, but the FDA clearance implies US-based or FDA-accepted international clinical trials. It's a prospective study.
- Non-clinical Studies: Performed internally at one site (Lot-to-Lot Precision) or at three external sites (Site-to-Site Reproducibility). These are also prospective experimental studies.
3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts (e.g. radiologist with 10 years of experience)
- The ground truth for the clinical test set was established using an "FDA-cleared molecular comparator method." This is a laboratory-based, highly sensitive, and specific molecular test, which serves as the gold standard for detecting influenza RNA/DNA.
- There is no mention of human experts (e.g., radiologists, pathologists) being used to establish the ground truth for this in vitro diagnostic device. The comparator method itself is the "expert" ground truth.
4. Adjudication method (e.g. 2+1, 3+1, none) for the test set
- The document does not describe an adjudication method for conflicting results between the investigational device and the comparator method. Results from the WELLlife Flu A&B Home Test were compared directly to the FDA-cleared molecular comparator method. For an in-vitro diagnostic, typically the molecular comparator is considered the definitive truth.
5. If a multi reader multi case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance
- No MRMC study was performed. This device is a lateral flow immunochromatographic assay, a rapid antigen test that produces visible lines interpreted directly by the user (either a lay user at home or a professional user). It does not involve "human readers" interpreting complex images or AI assistance in the interpretation of results in the way an imaging AI device would. Therefore, this question is not applicable to the WELLlife Flu A&B Home Test.
6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done
- This question is primarily relevant for AI/ML-driven software as a medical device (SaMD) where an algorithm provides an output. The WELLlife Flu A&B Home Test is a rapid diagnostic test interpreted visually. Its performance is inherent to the chemical reactions on the test strip, and it's designed for human interpretation (either self-testing or professional use). Therefore, a "standalone algorithm-only" performance study is not applicable in the context of this device's technology. The "device performance" metrics (PPA, NPA) are effectively its standalone performance as interpreted by a human user following instructions.
7. The type of ground truth used (expert consensus, pathology, outcomes data, etc)
- The ground truth for the clinical study was an FDA-cleared molecular comparator method (e.g., PCR or equivalent), considered the gold standard for influenza detection.
8. The sample size for the training set
- The provided document describes clinical and non-clinical performance evaluation studies. For IVD devices like this one, it's common that the "training set" is not a distinct, formally defined dataset as it would be for a machine learning model. Instead, the device's design, reagent formulation, and manufacturing processes are optimized and validated through iterative development and verification testing (analogue to "training" and "internal validation"). The studies described in this summary are primarily validation studies demonstrating the final product's performance. Therefore, a specific "training set sample size" as one might see for an AI model is not applicable/not explicitly defined in this context.
9. How the ground truth for the training set was established
- As mentioned above, for a rapid diagnostic test, there isn't a "training set" in the sense of a machine learning model. Instead, the development process involves:
- Analytical Validation: Establishing LoD, reactivity, specificity (cross-reactivity, interference) using reference strains, cultured microorganisms, and purified substances with known concentrations and characteristics. This essentially acts as the "ground truth" during the development phase.
- Design Iteration: The test components (antibodies, membrane, buffer) are optimized to achieve desired sensitivity and specificity against known influenza strains and potential interferents. This iterative process, using well-characterized samples, ensures the device learns (is developed) to correctly identify targets.
- The FDA-cleared molecular comparator assays serve as the ultimate "ground truth" against which the device's overall clinical performance is measured.
N/A