BCG vaccine: what the TB jab protects against and why it leaves a scar

BCG (Bacillus Calmette-Guerin) is the vaccine against tuberculosis (TB) that most babies in Singapore get soon after birth, usually before you leave the hospital. HealthHub says it is highly effective in preventing serious forms of childhood TB, such as TB meningitis. It is a single dose into the skin. A few weeks later a small boil usually forms at the spot and heals into a scar.

When your baby gets the BCG vaccine

HealthHub says the BCG vaccine is routinely given to newborns in Singapore soon after birth, as part of the NCIS. It is one injection into the skin, and it is usually offered while your baby is still in hospital. MOH's schedule table puts BCG at birth, next to the first hepatitis B dose, and notes that both are typically given in hospitals.

If your baby left hospital without it, HealthHub says BCG can still be given as one dose to children up to 5 years of age. From 6 months old, your child needs a Mantoux test first, a skin test that checks for TB infection. Do not plan on the polyclinic for this one: NHG Polyclinics says it stopped giving BCG on 2 January 2016 and asks parents to check with the hospitals directly.

What BCG protects your child from

TB is a bacterial infection that spreads from person to person through droplets in the air, for example from a cough or a sneeze, HealthHub says. HealthHub also says BCG is highly effective against the serious forms of childhood TB: TB meningitis, an inflammation of the covering of the brain or spinal cord, and disseminated TB, where the infection spreads from the lungs to other organs.

KKH's Infectious Disease Service, writing for SingHealth, puts numbers on it: BCG cuts the risk of all forms of TB by 50% and of deadly forms by up to 80%. It also says TB is still common in Singapore, even though rates have fallen a lot since the 1950s.

The BCG scar: what normal healing looks like

The jab site keeps changing for weeks, and that is expected. KKH describes the usual course. A raised red mark appears right after the injection and fades within half an hour. After two to three weeks a small, firm red lump comes up and grows for about a week. It fills with pus-like material, bursts and leaves a shallow ulcer. KKH adds that some parents may not even notice this stage.

KKH says you do not need a plaster, ointment or powder on it. If there is a lot of pus, a light sterile gauze that lets fluid through is fine, and HealthHub says to keep the area clean and dry. By the 12th week healing is usually complete, KKH says, and a small permanent scar may be left as a sign of the vaccination.

When to see a doctor about the BCG site

KKH says about one in 1,000 babies develop a complication. Take your baby to a doctor if you see either of these:

• an abscess or pus collection at the BCG site that is still there after the 12th week
• a swollen lymph node, a small fleshy lump in the armpit (if the jab was in the arm) or the groin (if it was in the buttock), which may fill with or leak pus

HealthHub lists the signs of an allergic reaction to report to a healthcare professional straight away: a swollen face, eyes, lips or tongue, difficulty breathing, or itchy rashes over the whole body. For a fever that does not go away, HealthHub says see a doctor. The dose goes into your baby's Health Booklet, and the vaccination schedule tool lists the jabs that come next.

Frequently asked questions

What is BCG?

BCG is the tuberculosis vaccine, named after Bacillus Calmette-Guerin. KKH says it contains a weakened form of live bacteria related to TB, given at levels that do not cause the disease, so the body makes antibodies to fight TB.

Is a boil or ulcer after BCG normal?

Yes. HealthHub says a small boil may develop 2 to 3 weeks after the jab. KKH says it usually becomes a shallow ulcer that has healed by the 12th week. See a doctor if it is still discharging after that, or if a lump appears in the armpit or groin.

Does every baby get a BCG scar?

Usually. HealthHub says the ulcer heals on its own, usually by 3 months, to a superficial scar, and KKH says a small permanent scar may be left as evidence of the vaccination.

My baby missed BCG at birth. What now?

Ask a hospital, since NHG Polyclinics stopped giving BCG in 2016. HealthHub says children up to 5 years old can have one dose, and a child aged 6 months or older needs a Mantoux test before the jab.

Related terms

• NCIS (National Childhood Immunisation Schedule): Singapore's official list of recommended childhood vaccines and the age each dose is due, from birth to 17 years.
• Health Booklet: The Child Health Booklet every Singapore baby gets at delivery. It records growth, milestones and every vaccination.
• Polyclinic: A public primary care clinic with subsidised fees, where Singapore families can take children for jabs and checks.
• Neonate (Newborn): The medical word for a newborn baby in the first 28 days of life.
• DTaP (Diphtheria, Tetanus and acellular Pertussis): The diphtheria, tetanus and whooping cough vaccine, given inside the 6-in-1 and 5-in-1 jabs from 2 months.

See every term in the glossary