How your baby's immune system develops

Your immune system is a network of cells and proteins that work together to protect your body and fight germs that cause infection.

Germs such as bacteria and viruses are sometimes described as 'foreign'. Some germs can cause your baby to become sick.

If bacteria or viruses get into your baby's body, their immune system acts quickly.

White blood cells respond by recognising the germ as something foreign. They make special proteins called 'antibodies' that help fight the infection.

Once these antibodies are made, the immune system 'remembers' the germ. This means the body can respond more quickly and effectively if the same germ returns. This memory is called 'immunity'.

Your baby's immune system is not fully developed when they are born. As your baby grows, it gets stronger.

During your third trimester of pregnancy, antibodies from your immune system are shared with your baby through the placenta. The type of antibodies that pass to your baby depends on your own immunity. In this way, your baby may be protected against the germs in your environment.

Your antibodies help protect your baby when they are born. They stay in your baby's body for weeks or months after birth. Your antibodies can help your baby fight diseases before they get their first vaccines.

Not all bacteria are harmful or cause disease. Some bacteria are helpful, including 'good bacteria' in your gut (digestive system) that help your immune system work well. They are passed on to your baby during a vaginal birth. This helps good bacteria establish in your baby's gut.

After your baby is born, they can get more antibodies during breastfeeding, especially in colostrum (the first breast milk). Antibodies continue to be passed to your baby in breast milk.

Premature babies do not get as many antibodies through the placenta as full-term babies. Their immune systems are less strong.

Premature babies are more likely to get sick from germs such as bacteria and viruses. Vaccinations for parents, family members and carers can help protect a premature baby from illness. Encourage family members and carers to talk to their doctor about booster vaccines.

Premature babies should get their vaccines, following the same schedule as full-term babies.

Visit the National Immunisation Program Schedule.

The protection your baby gets at birth only lasts a short time. It will gradually go away after a few weeks or months.

Just like adults, healthy babies make their own antibodies. Each time they are infected with a germ, their immune system starts to work. They make new antibodies that will protect them now and in the future.

Immunity in a baby is not as strong as in adults — it takes time to fully develop. In the meantime, there are some important things you can do to protect your baby, like breastfeeding and getting vaccinated on time.

Breast milk contains many good things to help build your baby's immune system. These include proteins, fats, and sugars. Breast milk also contains antibodies and probiotics.

When you breastfeed, antibodies that your immune system makes to fight infection are passed to your baby in your breast milk. This is how your breast milk can protect your baby from infections they are exposed to.

Breastfed babies have fewer infections. They also get over infections more quickly than formula-fed babies. While breastfeeding is good for your baby's developing immune system, it cannot fully protect them from all serious infections.

Some people cannot breastfeed, or choose not to. Infant formula is another healthy option for babies.

Vaccinating your baby is the safest and most effective way to protect them against many serious diseases.

Vaccination causes an immune response in the same way that a virus or bacteria would, without your baby actually getting sick.

The vaccine makes your baby 'immune'. If your baby is exposed to the germ in future, their immune system will remember it and an immune response will swing into action. It will fight off the disease and help prevent serious complications.

Your baby's first vaccines are offered at birth, then at 6 weeks, 4 months and 6 months of age. Other vaccines and boosters are offered over the first few years of life.

Learn more about vaccinations.

In most cases, breast milk or formula provides all the vitamins and minerals your baby needs. Giving extra vitamins is not usually recommended for babies.

Once your baby starts on solids, a range of fresh foods should be enough to keep their immune system healthy.

This can include different types of pureed vegetables and fruits. Try to keep breastfeeding at the same time as starting solid food.

Read more on introducing solid food.

Probiotics are live bacteria and yeasts. They are found in many foods and in some supplements. They can be purchased over-the-counter at a pharmacy, supermarket or health food store.

Taking antibiotics kills some of the good bacteria in your gut. These bacteria are important for immunity. Some people think that probiotics can boost immunity after they have had antibiotics.

Probiotics are safe to use in late pregnancy and after your baby is born. Research proving the benefits of probiotics for children is limited. Talk to your doctor before giving probiotics to your baby. Together you can decide if it is appropriate to give your baby probiotics.

• The Australian Breastfeeding Association has an information page about breastfeeding and immunity.
• You can visit the Department of Health, Disability and Ageing for more information about childhood immunisation.
• The Royal Children's Hospital Melbourne has a fact sheet about probiotics and babies.

Languages other than English

• The Sydney Children's Health Network fact sheet about common newborn concerns has been translated into many community languages.
• Read more on childhood vaccinations in a range of languages at the NSW Multicultural Health Communication Service.

Information for Aboriginal and/or Torres Strait Islander peoples

• The Australian Breastfeeding Association has a collection of resources about breastfeeding for Aboriginal and/or Torres Strait Islander peoples.
• Keeping Our Mob Healthy is a range of child health fact sheets developed specifically for Aboriginal children, young people and families.