For the first half year of life, a newborn’s immune system is not yet fully developed. In the months after birth, it relies on antibodies that the placenta delivers to the baby during birth. These antibodies provide a bridge from infancy to the time when the immune system is better able to function on its own.
A newborn’s immune system can get an extra boost from nursing. This is because each meal provides additional protective antibodies. The highest concentration of these can be found in colostrum, which is the thicker, more nutrient rich substance which forms the mother’s first milk. For this reason, babies who breastfeed tend to get sick less frequently and have less severe symptoms when they do become ill.
Despite these antibodies, a newborn’s immune system is still weak enough to warrant extra caution. This includes avoiding people who are sick and washing hands thoroughly before handling the baby. Due to their tendency to frequently harbor germs and minor illnesses such as colds, it may also be advisable to limit exposure to other young children when possible.
Another way to minimize risk to the newborn is to limit the people who handle the baby to family whenever possible. This is primarily because relatives share not only genes, but a common germ pool. As these germs are familiar to the mother and the baby she has been carrying, both are more likely to be able to launch a defense against them. For this reason, germs found in the hospital during the birthing process or from non-family are more likely to lead to a serious condition as the means to fight them are less easily attainable.
As a newborn’s immune system is still developing, any illnesses babies do get in the first months of life can be much more serious. Due to a limited ability to fight dangerous foreign matter, additional medical intervention may be required for something as simple as the common cold. In some cases, a doctor will require special observation, testing, and other precautions if a newborn gets sick at all.
There are several processes which lead to the development of a newborn’s immune system. One key change is the development of stomach acid, which helps to kill unwanted bacteria. Newly-produced trypsin and pepsin can also keep the small intestine sterile. There are physical changes, such as the development of protective membranes in the urinary and respiratory tracts, which can help to fight illness as well.