Source: Metropolis Express
According to the data released by Japan's National Health Crisis Management Research Institute on the 21st, from October 6th to 12th, more than 3,800 designated medical institutions in Japan reported more than 9,000 influenza cases, and the number of new cases per week has increased for eight consecutive weeks.
The latest data show that in the 41st week of 2025 (October 6-12), more than 3,800 medical establishments across Japan a total of 9,073 cases of influenza, averaging 2,36 cases per household, about 1.5 times the previous week and 2.65 times the same period last year.
According to Japan’s standards, the average number of cases of influenza per week by each medical establishment is more than 1, which marks the entry into the flu epidemic season, and if this number is more than 10, it reaches the “warning alert” level (lower than the alert level). According to this standard, in the 41st week of 2025, about two-thirds of the 47 prefectures across Japan have entered the flu season.
According to the latest data of the Japanese Ministry of Health and Labour, affected by the spread of the flu, as of the 12th, a total of 998 kindergartens, kindergartens, primary and secondary schools were shut down or part of the year, class stop, and only from October 6 to 12 this week there were 328 educational institutions shut down or part of the school.
The Ministry of Health and Labour of Japan announced on October 3 that the country has entered the flu season, five weeks earlier than in 2024.
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Recently, Japan has announced the entry of the influenza epidemic season. At the same time, monitoring data from the World Health Organization (WHO) show that influenza activity across the northern hemisphere is gradually heating up, and a "winter influenza season" is quietly approaching.
On October 21, the Infection Department of Huashan Hospital Affiliated to Fudan University issued a document, focusing on reminding: vaccination against influenza.
Selection of articles:
When the flu season comes, many people will ask: Doesn't flu happen every year? Why do you have to get vaccinated every year? And what do "strain change" and "mutation pressure" mean? Understand it in one article.
1. Flu ≠ common cold, it changes every year
influenza (influenza) is an acute respiratory infectious disease caused by influenza virus, which is mainly divided into types A, B and C.
Among them, type A virus (especially H1N1 and H3N2 subtypes) is the easiest to mutate, spread widely and cause severe disease. Virus B is relatively mild, but it can still cause severe illness in children and the elderly.
Why does the flu come every year? Because-the virus is getting too fast.
There are two key “spotting” proteins on the shell of the flu virus: hemoglobin (H) and neuronase (N). whenever it is replicated, its genes may have minor “spelling errors,” these accumulated changes are called antigenic drifts.
If it drifts too much, the old vaccine will no longer "recognize" the new virus.
H3N2: Scientists find it changed again
In 2025, the World Health Organization updated the recommended composition of the Northern Hemisphere influenza vaccine for 2025-2026.
One of the important changes is that the H3N2 subtype has been "replaced", and the new recommended virus is A/Croatia/10136RV/2023 (for egg-based vaccines) or A/District of Columbia/27/2023 (for cell culture vaccines).
This suggests that scientists have found in global surveillance that the original H3N2 virus has seen significant changes in the genetic and antigenic structure compared to the current epidemic strain.
If the old vaccine is not updated, its protection will decrease.
This is the so-called "variable stress": the virus continues to change in its spread, and the vaccine has to catch up. If the "recipe" is not updated, the recognition of the immune system will be discounted.
3. This year's fashion trend: H1N1 and H3N2 are still the protagonists
According to global flu monitoring data, the main likely outbreaks of the northern hemisphere flu season this year include:
A/H1N1pdm09: i.e., a virus that persisted after the 2009 pandemic;
A/H3N2: this year, the variation is active, and is a key prevention target;
Type B Victoria: milder, but common in children.
In Japan, influenza A is currently mainly prevalent, with H1N1 accounting for the majority and H3N2 showing a rising trend.
This means that this year's influenza season may come early, last long, and there may be multiple strains circulating in parallel.
4. Why do you have to get flu vaccine every year?
Viruses are changing, immunity is declining, and vaccines are catching up.
These three facts suffice to illustrate the importance of annual vaccination.
The virus changed: the vaccine formula is updated annually.
02 Immunity will attenuate: Antibodies usually last for 6-12 months.
03 Vaccines can prevent severe illness: they can significantly reduce the risk of hospitalization and death.
The latest data in the Southern Hemisphere show that the influenza vaccine protection rate this year is about 50%, meaning that one in two people will be protected from infection or severe illness.
5. When is the most appropriate time to play?
The Northern Hemisphere flu season usually begins in October and peaks in December-February.
It takes about two weeks to develop antibodies after vaccination.
10–November is the best window for vaccination, but even after vaccination is a protection.
Who should be prioritized?
• Elderly (≥ 60 years old)
Children (6 months – 5 years old)
• Chronic diseases
• Medical staff, teachers, public transport practitioners
• Pregnant women
7. Scientific protection, starting with one shot
The flu “changes” every year, but science can always follow in its footsteps.
Japan's early epidemic signals indicate that the virus may be more active this year.
And for us, the simplest and most effective action is to get the flu vaccine in advance.
Getting vaccinated is not about being afraid of the flu, but about making the flu afraid of you.
The scientific defense line starts with this needle.