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Difference Between Active and Passive Immunity

Medically Reviewed by Dan Brennan, MD on June 21, 2021

When strange bacteria and pathogens find their way into your body, they’re usually destroyed by your immune system. Before getting to your immune system, foreign material has to go through a few lines of defense that your body has in place. Active and passive immunity are the two most common ways that your immunity is strengthened.

What Are Active and Passive Immunity?

Your immunity grows stronger when there are antibodies to illnesses and diseases present. Antibodies’ purpose is to damage or kill foreign organisms that enter your body. Active and passive immunity both serve this purpose but are different in how antibodies are created.

‌Active Immunity. Active immunity is more common in our bodies than passive immunity. Our individual immune systems build up active immunity instinctively as we’re exposed to new bacteria and strange pathogens.

Active immunity happens in response to breathing new air, eating new food, and touching new things. People with average immune systems don’t get sick every time something new enters their body because active immunity is constantly working to neutralize foreign agents. Examples of active immunity are numberless because your body is exposed to and reacts to new pathogens every day.

Passive Immunity. Any contributions not made by the body are considered passive immunity. These are less common, but they are incredibly important because they let our bodies take a proactive defense against dangerous illnesses and diseases.

Pros and Cons of Active Immunity

A benefit of active immunity is that it lasts longer than passive immunity. Active immunity creates a certain kind of cell that has a long memory, and when they recognize a dangerous pathogen, their memory is triggered. The cells multiply and alert other parts of the immune system that something familiar is back, and they work together to fight something they know exactly how to defeat.

‌Although you typically take in foreign substances that aren’t life-threatening, it’s possible that you may come across something dangerous. Because active immunity is random, there’s more room for illness and disease.

Similarly, active immunity doesn’t protect you against mutations of diseases that your body already has antibodies to. When diseases mutate, they change structure in ways that your immune system isn’t prepared to fight.

Pros and Cons of Passive Immunity

Passive immunity is valuable to your health because you can be immediately prepared to fight specific, dangerous illnesses and diseases. It protects your body from things it might not be able to overcome on its own.

Additionally, passive immunity gives your immune system a boost immediately.

The greatest downside to passive immunity is that these antibodies don’t stay in the body for very long. Because your body isn’t continually reacting to specific pathogens, the antibodies that fight them will die off without restocking.

Examples of Passive Immunity

One of the most common instances of passive immunity happens between mothers and their children. Babies benefit from passive immunity via their mothers before they’re born and for a period of time afterwards. Their mother’s placenta and breastmilk offer something called maternal antibodies to help keep them healthy.

Placenta. Pregnant women give their babies nutrition and defense against illness through placentas and blood circulation. With blood, maternal antibodies and other immunity defenses travel to the unborn child. Although the baby is mostly safe from bacteria and illness before birth, immediately after leaving its mother’s body the baby is susceptible to them.

Breastmilk. Breastmilk offers maternal antibodies, too. Specifically, the colostrum produced by mothers immediately after birth helps pass along immunity. Colostrum has extremely high levels of antibodies that help protect the intestines and other important systems.

Immunity from the mother’s system prepares the child for whatever they come into contact with before they can build up their own immune system.

Vaccines are another common form of passive immunity. When you receive a vaccine, you are given a tiny dose of pathogens that your body is likely to defeat. After killing the foreign substances, your body builds up a temporary defense. For a period of time that varies by vaccine, your immune system is well-equipped to battle the same pathogens.

Your body needs to be continually introduced to new pathogens and other substances in order to stay healthy. Active and passive immunity both contribute to a well-equipped, strong immune system.

WebMD Medical Reference

Sources

SOURCES:

Centers for Disease Control and Prevention: “Immunity Types.”

Children’s Hospital of Philadelphia: “Types of Immunity.”

Medicine LibreTexts: “Active and Passive Humoral Immunity.”

Mucosal Immunology: “Passive Immunization.”

Occupational Medicine: “Active and passive immunity, vaccine types, excipients and licensing.”

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