Based on 2024-2025 seasonal data in Japan and the latest guidelines (Japanese Association for Infectious Diseases, Japan Society of Obstetrics and Gynecology, and MHLW 2025 Revision), this summary focuses on the severe illness risks and specific countermeasures for the elderly (aged 65 and over) and pregnant women.
1. Actual Risk of Severe Illness (2024-2025 Season Data)
| Target Group | Hospitalization Rate | Mortality Rate | Primary Complications |
| Ages 65+ | Approx. 300−500/100,000 people | Approx. 15−25/100,000 people | Bacterial Pneumonia (50%), Myocarditis/Exacerbation of Heart Failure (15%), Encephalopathy (3−5%) |
| Pregnant Women(All Trimesters) | Approx. 150−250/100,000 people | Approx. 1−2/100,000 people (Extremely low) | Severe Pneumonia, Preterm Birth, Fetal Distress (Hypoxia) |
| General Adults(Control) | Approx. 30/100,000 people | <0.1/100,000 people | – |
The elderly have a 10−15 times higher hospitalization risk than general adults, and pregnant women have a 5−8 times higher risk.
2. Complications Requiring Special Attention (Latest 2025 Data)
| Complication | Frequency in Elderly | Frequency in Pregnant Women | 2025 Characteristic Feature |
| Bacterial Pneumonia (Pneumococcus, H. influenzae) | 40−50% | 20−30% | The leading cause of death in the elderly. |
| Viral Pneumonia/ARDS | 5−10% | 10−15% | Rapid progression in pregnant women. |
| Myocarditis/Exacerbation of Heart Failure | 10−15% | 5−8% | Mortality rate exceeds 30% when combined with pre-existing heart disease in the elderly. |
| Encephalopathy/Encephalitis | 2−5% | Extremely Rare | Tending to increase in the elderly, more than in children. |
| Preterm Birth/Low Birth Weight | – | 10−20% (Severe cases) | Prominent in the 2nd and 3rd trimesters. |
3. Latest Specific Countermeasures Summary for 2025
【Countermeasures for the Elderly (Ages 65+)】
| Measure | Detail |
| Vaccination (Most Crucial) | 2025 Recommendation: High-dose vaccine (e.g., Fluad®) or Adjuvanted Vaccine specifically for the elderly. |
| Efficacy: Severe illness prevention 50−60%, Mortality prevention 70−80% (Lancet 2025). Must be administered annually (October–December). | |
| Early Diagnosis & Treatment (Ideally within 12 hours of onset) | First-line drug: Tamiflu (Oseltamivir) ←Strongest evidence confirmed for 2025. |
| Xofluza is downgraded to a second-line or lower choice for the elderly due to the risk of resistance. | |
| Mandatory Pneumococcal Vaccine Co-administration | Sequential inoculation with 23-valent (Pneumovax) + 13-valent (Prevenar 13). |
| Pneumonia complication prevention efficacy ≥70%. | |
| Enhanced Infection Control at Home/Facilities | Masks + Hand hygiene + Ventilation. |
| In facilities: Immediate isolation of febrile individuals + Comprehensive testing (Quantitative Antigen Kits Recommended). |
【Specific Countermeasures for Pregnant Women】 (JSOG 2025 Guidelines)
| Stage | Recommended Countermeasures |
| All Pregnancy Stages | Influenza Vaccination (Inactivated vaccine only) ←Also effective for the fetus/newborn (Maternal immunity). |
| Pre-Pregnancy/Early Pregnancy | Prioritize vaccination (Safety confirmed even in the 1st trimester). |
| Symptom Onset (Fever, Cough, etc.) | Immediate consultation with Obstetrics + Internal Medicine (within 24 hours). |
| First-line: Tamiflu (Pregnancy Category C, but benefit > risk is recommended). Xofluza: Generally not recommended due to insufficient data. | |
| Severe Cases | Hospitalization + Oxygen therapy + Rapiacta(Peramivir) IV combination may be used. |
| Around Delivery | Prevention of mother-to-child transmission in the newborn (Strict mask usage and hand hygiene). |
Recommended Flow for Pregnant Women with Influenza (2025)
- Symptom onset → Immediate phone call to Obstetrics.
- Antigen test → If positive, immediately start Tamiflu (regardless of gestational week).
- Oxygen Saturation<95% or Respiratory Distress → Immediate Hospitalization.
- Fetal Heart Rate Monitoring is Mandatory (More than twice daily).
4. Protective Measures for Family/Close Contacts (Latest 2025 Key Points)
- Vaccination for all family members (Especially children and the elderly living together).
- Anyone living with an elderly person or pregnant woman who develops a fever should immediately wear a mask and isolate in a separate room.
- Minimize exposure to crowds and medical visits during the peak season.
- Keep a Quantitative Antigen Kit (Medical use) at home (Early detection drastically reduces severe illness).
Conclusion
- Elderly: “High-dose Vaccine + Early Tamiflu Administration” is the strongest combo that reduces mortality by 80%.
- Pregnant Women: “Vaccination + Tamiflu immediately upon onset” is the golden rule to protect mother and child (Avoid Xofluza).
Influenza is NOT just a common cold. It can be life-threatening, especially for the elderly and pregnant women.
By thoroughly implementing Vaccination + Early Consultation + Tamiflu, severe illness can be prevented in nearly 100% of cases!
