INFLUENZA & COVID-19
Influenza and COVID-19 tests: methods, timing and accuracy
How visual antigen testing, IMMUNO AG and nodoca differ, including PCR-referenced studies and inconclusive COVID-19 results.
Medically reviewed by Koshiro Nishimoto, MD, PhD (Director)
Updated November 1, 2026
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Three assessment methods used at our clinic
| Method | How it works | Timing and features |
|---|---|---|
| Conventional antigen test (visual reading) | Reagents detect viral components in a nasal sample. Test lines are read visually. | Timing depends on the kit. Results must be read at its specified time. |
| IMMUNO AG | Uses a nasal sample. Silver amplification strengthens the detection signal, which is read automatically. | FluAB and COVID-19/FluAB: 3.5–15 minutes. Positive results may appear earlier; negative results generally require 15 minutes. Timing varies by cartridge. |
| nodoca | AI analyzes throat images, temperature and symptoms. It does not directly detect the virus. | Results take several to a little over ten seconds after imaging and data entry. No nasal swab is needed, although imaging can cause gagging. It does not distinguish influenza A from B. |
Times exclude registration, history taking, preparation and waiting. Fujifilm: cartridge specifications (Japanese) ／ nodoca FAQ (Japanese)
Fever level or symptom severity alone cannot determine viral load or whether a test will detect infection. We consider time since onset, exposure and the purpose of testing.
Understanding test accuracy
The following studies use PCR as the reference test. These are not results collected from patients at our clinic.
- Sensitivity: the proportion of PCR-positive people also identified as positive by the assessed test.
- Specificity: the proportion of PCR-negative people also identified as negative by the assessed test.
Antigen studies may use the terms positive and negative percent agreement, retained below. These values are not the probability that an individual positive or negative result is correct.
nodoca compared with PCR
| Condition | Sensitivity | Specificity |
|---|---|---|
| Influenza (659 cases) | 76.0% | 88.1% |
| COVID-19 (conclusive results only) | 80.3% | 77.9% |
In the COVID-19 evaluation, 72.8% of results were inconclusive.The COVID-19 sensitivity and specificity above apply only to conclusive results. An inconclusive result does not mean negative; the proportion varies between populations.
We therefore recommend nasal antigen testing or another suitable test when COVID-19 needs to be assessed. The nodoca COVID-19 function is an add-on to its influenza assessment.
Source: nodoca FAQ (Japanese) ／ PMDA: nodoca review (2022), p.24 (Japanese)
The 2022 approval evaluation did not demonstrate non-inferiority to conventional antigen testing. This was not a direct comparison with our clinic’s IMMUNO AG testing.
IMMUNO AG and other antigen tests
A 2015 study compared three influenza tests using nasal samples from 131 people. Comparator products are labelled Test 1 and Test 2 here.
| Test | A: positive / negative agreement | B: positive / negative agreement |
|---|---|---|
| IMMUNO AG FluAB | 100% ／ 96.0% | 86.7% ／ 98.3% |
| Test 1 (instrument reading) | 83.9% ／ 98.7% | 73.3% ／ 98.3% |
| Test 2 (visual reading) | 75.0% ／ 100% | 60.0% ／ 99.1% |
Positive and negative agreement correspond to sensitivity and specificity in this study. These are results for specific 2015 reagents, not all visually read kits or current combined influenza/COVID-19 tests.
Source: Takahashi et al., Japanese Journal of Medical Technology 2015;64:737–742 (Japanese)
The nodoca and antigen studies are separate. Their figures cannot be used alone to rank these methods.
Results are interpreted alongside the consultation
A negative result from any of these methods does not completely exclude infection. The doctor considers symptoms, their course and exposure, and decides whether further testing is needed.
Related information
Sources are linked beside the relevant text and tables. Medical information checked on November 1, 2026.