RSV in Japan: How to Protect Your Baby

What Is RSV?

RSV (Respiratory Syncytial Virus — RSウイルス — アールエスウイルス) is a common respiratory virus that causes cold-like symptoms in adults, but can be very serious — even life-threatening — in young babies.

According to Japan's Ministry of Health, Labour and Welfare, more than 50% of children are infected by age 1, and nearly 100% by age 2. RSV is one of the most important infections for new parents in Japan to be aware of, because there is no cure — only prevention.

Why Is It Dangerous for Babies?

For healthy adults and older children, RSV usually feels like a mild cold. But for young babies — especially newborns — the same virus can cause severe breathing difficulties requiring hospitalisation.

Babies at highest risk of severe illness:

• Newborns and babies under 6 months old
• Premature babies (早産児 — そうざんじ)
• Babies with congenital heart or lung conditions
• Babies with weakened immune systems

Infection from an older sibling or family member with a mild cold is one of the most common routes of transmission to newborns at home.

Symptoms & When to See a Doctor

RSV symptoms progress in two stages:

According to Japan's National Institute of Infectious Diseases, approximately 70% of first-time infected infants experience only mild upper respiratory symptoms and recover within a few days. However, around 30% progress to lower respiratory illness — including bronchiolitis (細気管支炎 — さいきかんしえん) or pneumonia (肺炎 — はいえん). RSV is also responsible for approximately 50% of all pneumonia cases in infants.

There Is No Treatment Drug

This is the most important thing parents need to understand: there is no antiviral drug for RSV. Once a baby is infected, doctors can only provide supportive care — oxygen, IV fluids, and monitoring. There is nothing that targets the virus itself.

How to Protect Your Baby — 2 Medical Options

Because there is no treatment, Japan now has two medical options to prevent severe RSV illness in infants. Many parents — and even some doctors — are not fully aware of both.

① RSV Vaccine for Pregnant Women (妊婦へのワクチン接種)

A vaccine given to the mother during pregnancy passes RSV-fighting antibodies through the placenta to the baby. This means your newborn is protected from birth — during the most vulnerable first months of life.

• When: Given during pregnancy (consult your obstetrician for timing)
• How it works: Maternal antibodies cross the placenta and protect the newborn
• Who it protects: The newborn, from the moment of birth

② Monoclonal Antibody for Newborns & Infants (新生児・乳児への抗体薬)

A monoclonal antibody injection (抗体薬 — こうたいやく) can be given directly to newborns and young babies to protect them against severe RSV illness. Unlike a vaccine, this is a ready-made antibody, not a live or inactivated virus.

• When: Given after birth, especially at the start of RSV season
• Who it is for: All newborns and infants — especially high-risk babies (premature, heart/lung conditions)
• How it works: Provides immediate antibody protection without requiring the baby's immune system to respond

Daily Prevention at Home

Even without medical intervention, there are important steps every family can take:

For the whole family

• Handwashing — thorough handwashing before touching the baby, especially after being outside
• Ventilation — keep rooms well ventilated
• Masks — any family member with cold symptoms should wear a mask around the baby
• Avoid taking newborns to crowded places, nurseries, or places with sick siblings during RSV season

For the baby's environment

• If possible, keep the baby's sleeping area separate from siblings who may have colds
• Regularly disinfect surfaces that are frequently touched

RSV protection works differently from the routine childhood vaccines. For what the standard schedule covers and what it doesn't, see our guide to Japan's childhood vaccination schedule.

📖 Japanese Vocabulary

Key terms for speaking with doctors or hospitals in Japan about RSV.