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While the criteria are generally the same for both children and adults, caution is especially advised for children, pregnant women, and the elderly, as they often have residual virus despite "looking well."The latest criteria from the Ministry of Health, Labour and Welfare and the Japanese Association for Infectious Diseases are summarized below.

Children are prone to more rapid deterioration than adults. A sudden high fever of ≥38.5∘C is almost always the first sign. The typical pattern is, "They were fine yesterday, but suddenly look lethargic..."Below is a table summarizing symptoms by age and time progression, based on the 2025 guidelines from the Ministry of Health, Labour and Welfare and the Japan Pediatric Society.

The most significant characteristic of the 2024–2025 season (especially with the dominant A/H3N2 strain) is the "abnormally persistent cough." There has been a sharp increase in individuals whose fever has subsided, but the cough persists for 2 to 6 weeks.

While you cannot "cure" influenza with OTC medicines after onset, you can "alleviate symptoms" and potentially "prevent deterioration." We have strictly selected only the medications actually sold in pharmacies that are genuinely useful for managing flu symptoms.

Seasonal influenza epidemics are accelerating nationwide. Daycare centers (for children aged 0-6) adhere to the School Health and Safety Act (specifying Type 2 Infectious Diseases) and the Child and Family Agency's "Guidelines for Infectious Disease Control in Daycare Centers." While daycare centers are not legally "schools," and thus the rules are not strictly mandatory, nearly all facilities adopt these standards. To prevent the spread of infection, prompt notification and compliance are essential.

If you contract seasonal influenza, you have the right to take leave from work. However, this is generally recognized not as a "legally mandated prohibition of attendance," but as a right to voluntary rest to protect your health, and an accommodation based on the company's duty of care for safety.As of 2025, the Labor Standards Act (LSA) does not specify compulsory attendance restrictions unique to influenza. However, in the interest of preventing the spread of infection, many companies establish rules referencing the standards of the School Health and Safety Act. Below is a summary of the relevant LSA provisions and key company rules, based on MHLW/Japanese Association for Infectious Diseases guidelines and practical case studies.

Based on a thorough analysis of 2025 real-world data (National Institute of Infectious Diseases, MHLW, as of November) comparing individuals who experienced co-infection versus those who avoided it, the following preventive measures are ranked by their proven efficacy.

Co-infection with Influenza and COVID-19, commonly known as "Flurona," has been confirmed in approximately 1,200 cases nationwide in Japan (as of November) and poses a severity risk incomparable to single-pathogen infections. Latest national data (MHLW, NIID) reveals that Flurona elevates the risk of hospitalization by 4−6 times and the mortality risk by up to 15 times. This article thoroughly compares the real danger of co-infection and the decisive differences in symptoms, based on the predominant strains in 2025. It is crucial to understand the worst-case scenario—the simultaneous onset of "Influenza's rapid high fever" and "COVID's breathlessness and persistent cough"—and to take action immediately upon symptom onset.

This summary provides the actual incidence rates and comprehensive management strategies for influenza vaccine side effects, based on the latest reports from the Ministry of Health, Labour and Welfare, PMDA data, and the Japanese Association for Infectious Diseases summary, covering the period from October 2025 to the present.

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.