What is Influenza?
Influenza is an acute respiratory infection caused by the influenza virus. Compared to the common cold, it is characterized by sudden high fever (38°C or higher), severe fatigue, joint pain, and muscle pain, and is highly contagious, typically spreading during the winter season each year.
In Japan, more than 10 million people are said to be infected annually, and administering antiviral drugs within 48 hours of onset is effective in shortening the duration of symptoms and preventing severe illness.
Don't dismiss it as "just a cold"
Influenza can lead to complications (pneumonia, otitis media, encephalopathy) and worsen existing medical conditions, making it particularly important for the elderly, infants, pregnant women, and individuals with underlying diseases to exercise caution. If you develop a fever or joint pain, seek medical attention promptly.
Types of Influenza
| Type | Characteristics |
|---|---|
| Type A | Most common, infects a wide range of hosts including humans, birds, and pigs. Subtypes change annually (e.g., H1N1, H3N2), causing major epidemics. |
| Type B | Infects only humans, prevalent after February, tends to have more gastrointestinal symptoms like abdominal pain and diarrhea than Type A. |
| Type C | Mild in infants, sporadic. |
Symptoms
Typical Symptoms (Differences from the Common Cold)
| Symptom | Influenza | Cold |
|---|---|---|
| Fever | Sudden high fever of 38-40°C or higher | Low-grade fever to about 38°C |
| Onset | Sudden onset (worsens in a few hours) | Gradual worsening |
| General malaise | Severe | Mild |
| Joint pain/muscle pain | Severe | Almost none |
| Headache | Severe | Mild |
| Runny nose/cough | Appears later | Primary symptoms from early on |
| Sore throat | Present | Primary symptom |
| Gastrointestinal symptoms | Common with Type B | Rare |
| Duration | 3-7 days | 1-2 weeks |
Complications
- Pneumonia (bacterial secondary infection, viral)
- Otitis media (common in children)
- Bronchitis
- Sinusitis
- Myocarditis/Pericarditis
- Encephalopathy (severe in children and the elderly)
- Worsening of underlying medical conditions (asthma, COPD, diabetes, heart failure, etc.)
- Febrile seizures (infants)
Optimal Timing for Rapid Testing
Highest accuracy between 12 and 48 hours after onset
Influenza rapid tests are considered most accurate between 12 and 48 hours after symptom onset. Since the viral load is low within 6 hours of onset, there's a possibility of a false negative. If symptoms are severe but the test is negative, retesting on a subsequent day is recommended.
| Time from Onset | Test Accuracy | Recommendation |
|---|---|---|
| 0-12 hours | Low (many false negatives) | Retesting after 12 hours recommended |
| 12-48 hours | Highest | Recommended testing window |
| 48-72 hours | Slightly decreased | Still possible to test and treat |
| After 72 hours | Decreased | Testing is possible but medication effectiveness is limited |
Our Clinic's Testing Options
- Influenza rapid antigen test (Type A, Type B): Results in approximately 15 minutes
- COVID-19 and influenza co-test: Detects both with a single test
- Also supports highly sensitive next-generation testing equipment (improves early detection rate)
Treatment Options
Antiviral Drugs for Influenza
Starting treatment within 48 hours of onset can shorten the fever duration by 1-2 days and reduce the risk of severe illness and complications.
| Drug | Form/Dosage | Characteristics |
|---|---|---|
| Oseltamivir (Tamiflu) | Capsule/dry syrup, twice daily for 5 days | Most commonly used, for children to adults |
| Zanamivir (Relenza) | Inhalation, twice daily for 5 days | For ages 5 and up, sometimes considered first-line for pregnant women |
| Laninamivir (Inavir) | Inhalation, single dose | Treatment completed in one dose, for ages 10 and up |
| Baloxavir (Xofluza) | Oral, single dose | Treatment completed in one dose, for ages 12 and up (caution for under 12) |
| Peramivir (Rapiacta) | Intravenous infusion, single dose | When oral administration is difficult, for severe cases |
Abnormal behavior after taking Tamiflu/Relenza
Reports of abnormal behavior (such as jumping) in teenagers have led to warnings to not leave children and adolescents unsupervised for at least two days after symptom onset. Even without medication, influenza itself can cause neurological symptoms, so monitoring is crucial regardless of medication use.
Symptomatic Treatment
- Acetaminophen: For fever and pain (safe for pregnant women and children)
- Expectorants: For phlegm
- Antitussives: For severe cough
- Intravenous fluids: For severe dehydration
Do not use aspirin-based drugs for influenza
Using aspirin (Bufferin), diclofenac, mefenamic acid, etc. in influenza patients under 15 years old carries a risk of Reye's syndrome (acute encephalopathy + liver damage). Please use acetaminophen (Calonal).
Individuals at High Risk of Severe Illness
The following individuals are more susceptible to severe illness, making prompt medical consultation and early treatment particularly important.
- Elderly individuals aged 65 and over
- Pregnant women and women within 2 weeks postpartum
- Infants aged 2 and under
- Chronic respiratory diseases (asthma, COPD)
- Chronic heart, kidney, or liver diseases
- Diabetes, metabolic diseases
- Immunocompromised states (steroids, anticancer drugs, HIV)
- Neurological or neuromuscular diseases
- Obesity with a BMI of 30 or higher
About Influenza Vaccine
The vaccine is said to have an onset prevention rate of 30-60% and a severe illness prevention rate of 70-80%, and is especially important for the elderly and those with underlying medical conditions.
Types of Vaccines
| Type | Target | Characteristics |
|---|---|---|
| Inactivated vaccine (injection) | 6 months to all ages | Conventional type, routine vaccination (elderly) / optional (others) |
| Live attenuated nasal vaccine (FluMist) | 2-18 years old | Nasal spray, no pain |
| High-dose vaccine | 65 years and older | 4 times the standard dose, improved efficacy |
Vaccination Timing
- The best time is annually between late October and November
- Effectiveness begins in about 2 weeks
- Effectiveness lasts for about 5 months
- Children under 12 require two doses (3-4 weeks apart)
Infection Prevention and Home Measures
Daily Prevention
- Handwashing, gargling, alcohol disinfection
- Wearing masks (especially during peak season and in crowded places)
- Humidifying rooms (50-60% humidity)
- Sufficient sleep, nutrition, and exercise
- Annual vaccination
If a Family Member is Infected
- Infected individuals should recuperate in a private room, use a separate room
- Avoid sharing towels and dishes
- Frequent ventilation
- All family members wear masks
- Consider prophylactic administration if high-risk individuals are present
School/Work Absence Period
| Category | School Health and Safety Act |
|---|---|
| Infants (kindergarten/preschool) | Until 5 days have passed since onset and 3 days have passed since fever resolution |
| Children/Students (school) | Until 5 days have passed since onset and 2 days have passed since fever resolution |
| Adults (workplace) | No legal requirement, but approximately 48 hours after fever resolution is a guideline |
When to See a Doctor Immediately for These Symptoms
The following symptoms indicate a high-priority emergency
These are signs of severe illness. Consider emergency medical attention even at night or on holidays.
- Difficulty breathing or chest pain
- Lethargic with slow responses or impaired consciousness
- Experienced seizures
- Abnormal speech/behavior, hallucinations, or suddenly running (especially in children)
- Unable to drink fluids or no urination
- Purple lips or cold sweat
- High fever lasting for more than 3 days
- High fever returning after fever resolution (biphasic fever = possible pneumonia)
Features of Influenza Care at Our Clinic
- Rapid antigen tests determine Type A/B in approximately 15 minutes
- Also supports simultaneous COVID-19 and influenza testing
- Prescribes all types of antiviral drugs for influenza (Tamiflu, Inavir, Xofluza, etc.)
- IV drip available for dehydration
- Prompt referral to specialists for those at high risk of severe illness
- Influenza vaccination (October-December)
- Advice on preventing household transmission
- No appointment needed, same-day visits OK / Open daily 9 AM - 9 PM / 1-minute walk from Jujo Station
Be mindful of the 48-hour window from onset
If you wake up with a fever or joint pain, it's ideal to see a doctor on the same day. Starting appropriate medication while symptoms are mild can shorten the fever duration by 1-2 days.
