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Active vs Passive Immunity: Differences and Definition

Active vs Passive Immunity: Differences and Definition

Active vs Passive Immunity: Differences and Definition

Active vs Passive Immunity: Differences and Definition

A boy receives the Schick Test from a doctor in 1915. The Schick Test is a measure of immunity to diphtheria. Credit: Photo by National Cancer Institute on Unsplash https://unsplash.com/photos/DAW9lgNkwYw
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Immunity is defined as the body’s ability to protect itself from an infectious disease. When you are immune to a disease, your immune system can fight off infection from it.

Immunity is either innate or adaptive. Innate immunity, also known as natural or genetic immunity, is immunity that an organism is born with. This type of immunity is encoded in one’s genes. Genetic immunity protects an organism throughout their entire life. Innate immunity consists of:

  • External defenses: Known as the first line of defense, external defenses work to protect an organism from pathogen exposure. External defenses include things like the skin, tears, and stomach acid.
  • Internal defenses: Known as the second line of defense, internal defenses address a pathogen once it has entered the body. Internal defenses include things like inflammation and fevers. 

Adaptive immunity, also known as acquired immunity, is the third line of defense. Adaptive immunity protects an organism from a specific pathogen. Adaptive immunity is further broken down into two subgroups: active immunity and passive immunity. In this article, we will explore active and passive immunity.

What is active immunity?

Active immunity is defined as immunity to a pathogen that occurs following exposure to said pathogen.

When the body is exposed to a novel disease agent, B cells, a type of white blood cell, create antibodies that assist in destroying or neutralizing the disease agent. Antibodies are y-shaped proteins that are capable of binding to sites on toxins or pathogens called antigens.

Antibodies are disease-specific, meaning that each antibody protects the body from only one disease agent. For instance, antibodies produced when the body detects the virus that causes mumps will not provide any defense against cold or flu viruses.

A diagram showing the different types of active and passive immunity

When B cells encounter a pathogen, they create memory cells in addition to antibodies. Memory cells are a type of B cell produced following the primary infection that can recognize the pathogen. Memory cells can survive for decades, waiting within the body until the pathogen invades again. When the body is exposed to the pathogen for a second time, the immune response is more robust, quickly addressing the disease agent.

Immunity does not happen immediately upon disease exposure. It can take days or weeks after the first exposure for active immunity to develop. But once it does so, the protection can last an entire lifetime.

Active immunity can occur in one of two ways: naturally or via an immunization.

Natural immunity

Natural immunity is created when a person becomes infected by a disease. Take, for instance, someone who becomes infected with chickenpox. After the initial infection, the body builds immunity against the disease. This natural active immunity is why people who catch chicken pox are immune for many decades against the disease.

Vaccine-induced immunity

Also known as artificial active immunity, a person can build a resistance to a disease following an immunization. An immunization is defined as the process by which someone becomes protected against a specific disease via the administration of a vaccine.

Vaccines use a weakened or dead form of a disease to stimulate an immune response. Vaccines are typically administered using an injection. However, there are vaccinations administered via the mouth or as a nasal spray.

When a person’s immune system detects the weakened or dead pathogen, it begins to take steps to destroy it. This includes forming new antibodies and memory cells specific to that pathogen. In the future, if the body is exposed to said pathogen, antibodies will be created to protect the body.

Vaccination and immunity are essential for keeping large populations of people safe from infectious diseases. For instance, the
flu vaccine prevents millions of people from becoming infected with the flu every year.

What is passive immunity?

Passive immunity is protection from a disease provided by antibodies created outside of the body. Passive immunity:

  • Does not require previous exposure to a disease agent
  • Takes effect immediately
  • Does not last long (up to a few months)

What is the difference between artificial passive immunity and natural passive immunity?

Passive immunity is either maternal or artificial.

Maternal passive immunity, or natural passive immunity, is immunity passed along from mother to child. Before the child is born, antibodies are passed through the placenta to protect the child from illness. After birth, an infant continues to receive passive immunity to disease from antibodies found in breast milk.

Artificial passive immunity comes from injected antibodies created within a different person or an animal. These antibody-containing preparations are termed antiserum. The rabies vaccine and snake antivenom are two examples of antiserums that yield passive immunity.

Active vs passive immunity

Active ImmunityPassive Immunity
AntibodiesProduced inside of the body
Introduced from outside of the body
Results from
  • Direct infection
  • Vaccination
  • Breast milk
  • Injection
  • Mother to baby through the placenta
Takes effectOver time (typically several weeks)
Length of efficacyLong-term to lifelongShort-term
Produced by memory cells?YesNo