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Passive Immunity for Infants

By on March 13, 2018
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The body’s immune responses are broken down into two major types: innate and adaptive. Innate immunity, as the term implies, is naturally or genetically acquired. It includes the skin, the cells, and the proteins found in the body, and it acts as the first line of defense against different types of pathogens.

Adaptive immunity, on the other hand, targets specific pathogens. It is further divided into two types – passive and active. The difference between the two is that active immunity is developed by the body, while passive immunity is acquired, or “borrowed,” from an external host. This article sheds more light on the importance of passive immunity.

Passive Immunity

Passive immunity, which can either be naturally or artificially induced, works by acquiring ready-made antibodies from an immune host. Since the body does not need to be exposed to an infectious agent to be able to create a line of defense, it can immediately respond to a pathogen to prevent diseases. However, unlike active immunity, the effect of passive immunity is short term since it does not activate the memory cells, which can only be triggered once the body is already exposed to the pathogen. Nonetheless, passive immunity is critical for both fetal and newborn care and overall disease prevention.

Naturally Acquired Passive Immunity

During Pregnancy

Naturally acquired passive immunity plays a major role in protecting fetuses and infants from bacterial and viral infection. During pregnancy, maternal antibodies called immunoglobulin g (IgG) are transported across the placenta to the bloodstream of the fetus. These maternal antibodies are able to protect the newborn baby for six to eight months after childbirth. Despite offering short-term protection, maternal IgG antibodies are crucial for allowing the infant’s immune system to fully mature, especially since newborns only begin to develop their own IgG antibodies after birth.


Newborn babies can acquire a new set of antibodies via breastfeeding. Colostrum, which is the first substance secreted by the mammary glands after childbirth, is rich in secretory immunoglobulin (IgA) antibodies that protect the baby from infection. Unlike IgG that works from the bloodstream, IgA creates a line of defense in the baby’s gastrointestinal tract. It protects the baby’s intestines, airway, throat, and mouth until the mother decides to stop breastfeeding.

As a summary, below is the difference between IgG and IgA:

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Artificially Acquired Passive Immunity

Artificially induced passive immunity is a type of immunization used primarily for adults and children who have a compromised or weakened immune system. Typically administered via the vein, the highly concentrated antibodies used during passive immunization are taken from donors who have developed a strong immunity against specific diseases. It can also be administered as an animal or human blood plasma or as a monoclonal antibody. Additionally, passive immunization is widely used as a treatment for poisoning and acute infection.


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