“I’ll wear a mask if I get a fever,” “I’ll rest if I feel sluggish”—we tend to think this way about influenza. However, are you aware that this very perception is a major cause of infection spread?
Alarmingly, influenza begins spreading the virus to others during the completely asymptomatic incubation period.Even more frightening is the data indicating that the period immediately preceding the onset of symptoms is when infectivity is at its highest.
Summary of Symptoms During the Influenza Incubation Period
| Period | Presence/Absence of Symptoms | Details |
| Incubation Period(Infection to pre-onset) | Almost 100% Asymptomatic | * No fever. * No sluggishness or fatigue. * No sore throat or runny nose. Completely the same condition as a “healthy person.” |
| Exceptions (Very Rare) | Some feel very slight discomfort | * “Does my throat feel scratchy?” * “Maybe I’m a little tired?” * This is usually indistinguishable from a common cold. |
| Moment of Onset | Sudden, dramatic impact | Typical Pattern: Fine until noon → Chills begin in the early afternoon →High fever of 38−40∘C + body aches upon returning home. |
Infectivity During the Incubation Period
| Period | Ability to Transmit to Others |
| Incubation Period (Asymptomatic) | Already contagious!! (Infectivity is reportedly highest 24 hours before the onset of symptoms). |
| Day of Onset | Peak Infectivity |
| Post-Fever Resolution | Generally, infectivity becomes almost zero 1–2 days after the fever breaks (longer for children). |
✅ Summary
- During the incubation period, you are “completely unaware yourself,” but highly likely to be spreading the virus widely to those around you.
- Waiting until “I get a fever, then I’ll wear a mask” is too late.
- If someone in your family or workplace gets the flu, assume you might be in the incubation period and take early preventive actions (masking and hand hygiene).
At-Home Testing Kit Ranking (Combined COVID-19 and Influenza)
Here is the English translation of the ranking table for at-home diagnostic kits that test for both COVID-19 and Influenza A/B:
| Rank | Product Name (Manufacturer) | Targets Detected | Sensitivity (Detection Rate) (Estimate: 12-48h Post-Onset) | Result Time | Approximate Price (Per Test) | Suitability for Pregnant Women / Children | Key Features & Availability |
| 1 | Panbio COVID-19/Flu A&B | COVID + Flu A/B | COVID: Approx. 90% | Flu: Approx. 85% | 15 mins | ¥1,980 – ¥2,480 | ◎ (Shallow Nasal Swab) |
| 2 | クイックナビ-Flu+COVID | Same (COVID + Flu A/B) | COVID: 88% | Flu: 80–85% | 15–20 mins | ¥1,780 – ¥2,200 | ◎ (Designed for children’s use) |
| 3 | KBMラインチェック nCoV/Flu | Same (COVID + Flu A/B) | COVID: 85% | Flu: Approx. 80% | 15 mins | ¥1,480 – ¥1,980 | ◎ |
| 4 | イージードック Flu＆COVID-19 | Same (COVID + Flu A/B) | COVID: 87% | Flu: 82% | 15 mins | ¥2,200 – ¥2,600 | ◎ (Many cases of use by pregnant women) |
