① Seasonal Influenza A (Flu)

Seasonal influenza A is already spreading, and many areas in Japan are at a high alert level.
This year, the flu season started earlier than usual. Other types, such as Influenza B, and new variants that can partially avoid immunity, are also expected.

Even if you have received a flu vaccine, you can still get infected, so please continue to take precautions.

The flu vaccination season is almost over.
It takes about 2 weeks after vaccination for your body to develop protection, so early vaccination is strongly recommended.

If you get the flu, early testing and treatment help you recover faster.
Older adults, young children, and people with chronic illnesses should:

• Wash hands and gargle regularly
• Visit a clinic or hospital promptly if you feel unwell

② Infectious Gastroenteritis (Stomach Flu)

(Norovirus, Rotavirus, Sapovirus)

Viral gastroenteritis often increases during winter.
Common symptoms include:

• Fever
• Vomiting
• Watery diarrhea
• Abdominal pain

Cases are currently increasing.

Severe or frequent diarrhea can cause dehydration, especially in elderly people and young children.
In some cases, intravenous fluids (IV drip) may be needed.

These infections spread easily, especially in groups. Please take care with:

• Careful handwashing
• Cleaning toilets properly
• If there is vomiting or diarrhea, use chlorine-based disinfectants (bleach)

③ Respiratory Syncytial Virus (RSV)

RSV cases are reported in various areas of Japan, but there is no large outbreak at this time.

However, babies under 1 year old may become seriously ill.

If you have symptoms such as coughing:

• Wear a mask
• Avoid close contact to protect others

④ COVID-19

COVID-19 cases continue to be reported, but numbers are not high enough for a major outbreak at present.
There are regional differences, with more cases in large cities.

Other Infectious Diseases

The following infections are also increasing:

• Human metapneumovirus
• Whooping cough (Pertussis)
• Mycoplasma infection
• Streptococcal infection
• Hand, foot, and mouth disease
• Adenovirus infection (pharyngoconjunctival fever)

To protect yourself and others, please:

• Wash your hands frequently
• Gargle
• Brush your teeth regularly
• Eat balanced meals
• Get enough sleep

Information sources:

Ministry of Health, Labour and Welfare, Japan
Influenza Reports, 2025–2026 Season

Tokyo Metropolitan Infectious Disease Surveillance Center