You know that your body makes antibodies to fend off disease-causing organisms. But have you ever wondered how your body acquires immunity if it fails to develop antibodies naturally? Passive immunity makes this possible.
This type of immunity can be gained naturally or artificially to fight-off infections.
Let’s take a closer look at passive immunity, the different types, and its benefits.
What Is Passive Immunity?
Passive immunity is acquired when you receive antibodies from any other immunized person. This immunity process is more common in people who are unable to make antibodies in their bodies or who are at high-risk to infections. Passive immunity provides immediate protection against any antigen and can be life-saving.
How Does Passive Immunity Work?
While newborns derive passive immunity from their mothers, it can also be acquired through injecting borrowed antibodies into your blood to fight off infections much faster.
However, passive immunity is short term, unlike active immunity which is long-lasting. That’s because, in passive immunity, the antibodies are borrowed from another person and not continuously replenished as it is in active immunity.
How Can Passive Immunity Be Acquired?
Passive immunity in unborn and newly born babies can be acquired from their mother’s immune system  either through the placenta or breast milk. This is also the natural way by which passive immunity is acquired.
1. The Placenta
The amount and type of antibodies passed to the baby depends on the mother's immunity. When the baby is in its mother's womb, her blood circulates through the placenta, a cord that connects the mother and the baby. Blood carrying nutrients and oxygen reach the developing fetus through the placenta. The placenta wall also passes the antibodies and immune system cells from the mother’s body to the fetus. Although babies are not usually exposed to any antigens in the womb, the antibodies found in the baby's blood immediately after birth are generally from the mother’s blood.
2. Breast Milk
Apart from the placenta, babies also derive passive immunity from their mother’s breast milk. Breastfeeding protects against infections during and most likely after lactation. It also protects the baby against certain immunologic diseases, including allergy. The first protein-rich version of the breast milk, also known as colostrum, is produced early, a few days after birth. This milk is high in antibodies and nutrients. This is how newborns derive immunity right after birth until they begin to develop their immune systems.
3. Immunoglobulin Treatments
Passive immunity can be derived in artificial ways too through injecting antibodies. Individuals at high risk are often treated with loaned antibodies from other people, animals, or those synthesized in a laboratory.
For example, people bitten by poisonous snakes are often treated with antivenom. Antivenom is nothing but a combination of antibodies specific to that particular snake produced when a person was exposed to such snake bites. Another typical example of immunoglobulin treatment can be seen in infants born to mothers infected with hepatitis B. To protect the newborns from becoming infected, they are administered antibodies along with vaccination.
Did You Know?
The first vaccine given to babies includes whooping cough and Haemophilus influenzae because passive immunity for these diseases diminishes the fastest. On the other hand, passive immunity for mumps, measles, and rubella can last up to a year. Hence, vaccination for these diseases is given when the child is a year old.
Passive Immunity Benefits
Passive immunization is quick acting which means it ensures immediate protection to the body. - typically within hours or days. It can be a great way to treat certain viral infections in immunocompromised patients. As a part of this treatment procedure, high dose intravenous immunoglobulin  are injected in patients suffering from cytomegalovirus, parvovirus B19, and enterovirus infections.
Passive immunity also works in treating toxic shock syndrome and refractory staphylococcal infections.
Researchers are now looking for passive immunity to treat those who are seriously ill with COVID-19. This is known as plasma treatment, where a blood product called convalescent plasma is used. Plasma is the portion of the blood that contains antibodies. People who were already infected with COVID-19 and recovered had antibodies in their plasma. When they choose to donate blood, their plasma is isolated and administered intravenously to critically ill people with COVID-19. The loaned antibodies in the patient's body fight with the COVID-19 antigens, thus helping the patient to recover.
Since COVID-19 is a new type of infection, scientists are still investigating to determine how effective this treatment is. More studies are needed to draw an inference.
How Long Does Passive Immunity Last?
Passive immunity does not last long. It hardly lasts for a few weeks or months.  In infants, the quantity of antibodies passed to the baby depends on the immunity of the mother. For example, if the mother had chickenpox, she would have developed antibodies that would pass through the placenta. But, if she never had chickenpox, she would not have antibodies developed for chickenpox. This means that the infant will not have passive immunity for chickenpox. Antibodies that pass through the placenta stay only for a few weeks or months, and eventually disappear.
Breastfed babies may have passive immunity for a longer time  since breast milk also contains the mother’s antibodies. Babies born prematurely are more prone to infections because they do not have as many antibodies from their mothers as a full-term baby has.
Why Is Passive Immunity Always Temporary?
In passive immunity, the antibodies are loaned and not produced by the person’s immune system itself. Hence, it persists as long as the antibodies circulate in the blood. Once it disappears, no new antibodies are replenished. Therefore, passive immunity is always temporary.
Passive Immunity Examples
While passive immunity is short-lived, it works right away, and hence it is preferred over active immunity in children or immunocompromised adults who are at high risk. For example, if a child suffers wild animal bites, passive rabies immunization is commonly administered.
For people travelling to any country affected by hepatitis, doctors recommend passive vaccination to prevent it. This immunization is usually given on the day of their journey to cover their travel time. However, this is not practiced much now as we already have vaccines for hepatitis A available.
Patients are actively treated with antibodies when they are infected with cytomegalovirus or diphtheria. Passive antibody treatment is also done to prevent disease after a high-risk person is exposed to pathogens like tetanus, measles, syncytial virus, rabies, chickenpox, hepatitis A, and hepatitis B.
Immunity is key to keep your body function run smoothly and prevent you from any disease. That’s why it’s extremely important to develop strong immunity by following a balanced diet, regularly working out, and practicing healthy lifestyle habits. Passive immunity may be short term, but it can shield your body against infections with immediate effect. It can be a lifesaver for children, immunocompromised individuals, and in specific cases where vaccination is impossible. Passive immunity can either be derived naturally or by artificial means. However, it does not create memory cells and that’s why it cannot last longer.
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