Guides · インフルエンザ · infuruenza

Flu Season in Japan — The Shot, the Clinic, and the School Return Rule

By Dr. Masa · physician licensed in Japan · Last updated October 2026

Every winter, influenza — インフルエンザ (infuruenza), usually shortened to infuru — works its way through Japanese schools, offices and trains. The system for dealing with it is well-worn: a shot in the autumn, a clinic visit when the fever starts, and a fixed rule about when children may go back to school. That last part is what surprises families from abroad, so it gets the most space here.

Flu season in Japan: when it runs, and the early start in 2026

In a typical year, flu in Japan builds through the winter and peaks between late January and early March.

2026 is not a typical year. On 28 August 2026 the Ministry of Health, Labour and Welfare (厚生労働省, Kōsei Rōdōshō) announced that the national flu season had begun — months earlier than the usual winter peak. In the week of 17–23 August, the average number of flu patients per reporting clinic reached 1.11, above the 1.00 used to mark the start of the season (the table at the end of this guide explains the levels). The ministry notes it is the second-earliest start since records began in 1999, after 2009, not counting 2023, when the previous season's epidemic never ended.

In practice: check now how your clinic takes bookings for the shot, and read the school rules below before you need them.

The flu shot: who pays, how many doses, and when

Japan splits vaccines into routine and voluntary; the vaccinations guide explains the split.

Routine (定期接種, teiki sesshu) covers two groups: everyone aged 65 and over, and people aged 60 to 64 whose heart, kidney or respiratory function — or immune function, because of HIV — is impaired to the point that daily life is severely limited. Your city or ward runs the routine programme, and its notice explains how to use it where you live.

Voluntary (任意接種, nin'i sesshu) covers everyone else. In the ministry's own words, it is in principle paid entirely out of pocket, and the price differs from one medical institution to the next. It is worth ringing two or three clinics near you.

How many doses depends on age:

• Under 13: two doses, two to four weeks apart. Babies from six months up to age 3 get a smaller dose (0.25 mL) than children aged 3 to 12 (0.5 mL); the clinic takes care of this.
• 13 and over: one or two doses. The doctor will tell you which.

The nasal spray. A live nasal-spray vaccine (経鼻弱毒生インフルエンザワクチン) was approved in Japan in March 2023 for ages 2 to under 19. It is a single dose of 0.2 mL, half in each nostril. Whether it suits your child is for the doctor to decide.

When. The ministry says it is best to finish vaccination by mid-December. For a child who needs two doses, that means starting early enough to fit both in.

Got a fever? The clinic and the five antivirals

When a fever comes on in flu season, the usual first stop is an ordinary clinic: 内科 (naika, internal medicine) for adults, 小児科 (shōnika, pediatrics) for children. It is worth phoning first to say you have a fever and ask how to come in.

Japan has five antiviral medicines for flu: oseltamivir, zanamivir, peramivir, laninamivir and baloxavir. According to the ministry, starting one within 48 hours of the illness beginning usually shortens the fever by one to two days. Whether you need one of these medicines at all is the examining doctor's decision.

The same goes for testing. Whether to do a rapid flu test (迅速検査, jinsoku kensa), and at what point, is up to the doctor who sees you.

Children and the first two days: the fall-prevention warning

One piece of Japanese flu advice deserves particular attention if you have children or teenagers.

The ministry warns about abnormal behaviour (異常行動, ijō kōdō) during flu, and stresses that it can happen whether or not a medicine has been taken, and whichever medicine it is. Its instruction to families is direct: for at least two days from the start of the fever, parents and carers should take steps to prevent accidents such as falls. The ministry's examples include:

• lock the front door and all windows
• have the child rest in a room that does not open onto a balcony
• if you have a room with window grilles, have the child sleep there

School and daycare: the "5 days + 2 (or 3)" rule

Under Article 19 of the School Health and Safety Act's enforcement regulations (学校保健安全法施行規則, Gakkō Hoken Anzen Hō Shikō Kisoku), a child with seasonal flu is suspended from attendance — 出席停止 (shusseki teishi) — until both of these are true:

1. five days have passed since the illness started, and
2. two days have passed since the fever went away — three days for kindergarten children.

Licensed nurseries (保育所, hoikusho) follow a guideline from the Children and Families Agency (こども家庭庁) that sets the same period as for kindergartens: five days after onset and three days after the fever goes.

How to count. The day symptoms start is day 0. The day the fever goes is also day 0. Counting begins the next day, and whichever condition finishes later decides the return date.

• Fever gone on a Monday → school from Thursday, nursery from Friday, as long as five days since onset have also passed.
• Illness started on a Wednesday → the earliest return to school is the following Tuesday, provided the fever was gone by Saturday (for nursery, by Friday).

Rather not count on your fingers? Our flu return-date calculator does it for you: enter the two dates and it shows the first day back under the rule.

What the rule leaves open. What counts as "fever gone", and what happens if the fever comes back, are questions for your school or your doctor. The same goes for certified childcare centres (認定こども園, nintei kodomo-en), international schools and universities. Ask the institution which rule it follows.

A doctor can shorten it. The regulation allows an exception when a school doctor or another physician judges, from the child's condition, that there is no risk of infection.

Paperwork. The ministry says schools do not need a recovery certificate or a negative test result. Some nurseries and kindergartens ask for a return form: a parent's form (登園届, tōen todoke) or a doctor's note (意見書, ikensho). Ask yours what it uses.

COVID-19 is different. The same article sets a separate rule: five days after onset, and one day after symptoms improve.

Work: company rules, and why you shouldn't need a certificate

Seasonal flu is a Category 5 infectious disease (5類感染症, go-rui kansenshō) under Japan's Infectious Diseases Control Act (感染症法, Kansenshō Hō). The Act's work restrictions (就業制限, shūgyō seigen) cover the more serious categories, not Category 5. The Infectious Diseases Control Act does not set how many days an adult with flu must stay off work.

Your employer's work rules (就業規則, shūgyō kisoku) may set one, so check them or ask HR.

What employers should not do is demand proof. The ministry's Q&A on influenza (in Japanese) is explicit: it is not desirable for a workplace to ask employees for a certificate of recovery (治癒証明書, chiyu shōmeisho) or a negative test result, and none is needed. If you are asked for one, that page (Question 20, version of 19 December 2025) is the document to point to.

When to see a doctor early

The ministry's guidance is plain: if you are unwell — a high fever that continues, difficulty breathing, or a change in how alert or conscious you are — see a doctor early.

At night or at the weekend, our after-hours care guide explains the advice lines and where to go. If it is an emergency, see the emergency page.

Checking flu levels in English

Flu numbers in Japan are reported per sentinel clinic (定点当たり, teiten atari). This is the average number of flu patients each designated reporting clinic sees in a week. Since 7 April 2025, those clinics have been the ones that report acute respiratory infections (急性呼吸器感染症) as a whole.

Health authorities read that number against three fixed levels:

For an English source, the Tokyo Metropolitan Infectious Disease Surveillance Center (東京都感染症情報センター) publishes weekly figures at its English page.

General information about how the system works, not medical advice for your situation. Whether you need a test, a medicine or time off is for the doctor who examines you. Schools, nurseries and employers apply these rules in their own way, and their instructions come first. Rules and figures as of September 2026.