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Humans have internal defence sy...Read More
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Written byLakshey Bahl
Reviewed byVaibhav Kumar
Last Modified 30th September 2026
Insurance Domain Expert
What is Immunity?
The body’s defence system triggers when harmful bacteria, viruses, or toxins expose it. It also stops the spread of diseases. The immune system achieves this goal through a network of cells, tissues, and proteins that identify and fight threats. The immune system can generally be categorised in two ways:
- Innate immunity is the body’s general, first line of defence. It protects against pathogens and other foreign bodies.
- The body develops adaptive immunity after exposure to specific pathogens through infections or vaccines.
Different Types of Immunities
The human immune system utilises multiple levels of protection to fight the antigens. These include active and passive immunization. Let's understand how these immunities work:
- Innate immunity: It is the first line of defence against foreign antigens and pathogens. It's present in the body from birth. It includes barriers such as the skin and inflammatory responses.
- Adaptive immunity: The body develops it over time after exposure to different pathogens through infections or vaccines.
- Active immunity: The body produces antibodies to eliminate the infection.
- Passive immunity: The body gets antibodies from outside sources. This includes transfer from the mother through the placenta or breast milk. It can also come from treatments like immunoglobulin or antiserum.
What is Active Immunity?
This immunity is a type of adaptive immunity. The body makes and uses its own antibodies to fight antigens. People achieve this through natural infection or vaccination.
In vaccination, scientists weaken the disease so the body learns to fight it. This can help the person become immune for years and even a lifetime.
The process that triggers active immunity is as follows: A pathogen enters the body naturally or through a vaccine. The immune system activates B cells in response. It then produces specific antibodies.
Once the antibodies eliminate the infection, the body produces memory cells to protect itself against future exposures. Active immunity is the basis of most vaccination programmes globally.
How Does the Body Develop Active Immunity?
Active immunity is acquired when a foreign substance (pathogen: virus, bacteria, toxin, etc.) is introduced into the body. A pathogen invades the body, and the immune system recognises it as non-self by its surface markers, called antigens.
This recognition triggers a series of immune responses:
This recognition triggers a series of immune responses:
- Detection: White blood cells, like phagocytes and dendritic cells recognise a pathogen when it enters one’s body. They can engulf it and present its antigens to other immune cells.
- Activation: Specialised immune cells called T cells help activate B cells and support the immune response.
- Antibody Production: B cells multiply and secrete antibodies to destroy the pathogen by specifically binding to it.
- Immunological Memory: After the infection is controlled, the body retains specific memory B and T cells. These cells can identify the same pathogen when they are re-exposed and can help the immune system respond more quickly.
How Vaccination Develops Active Immunity?
Vaccination simulates a natural infection to trigger an immune response without causing severe illness.
A vaccine is a safe version of a pathogen or one of its components that is introduced to a person. This may include a weakened or inactive pathogen, a specific protein, or genetic instructions such as an mRNA blueprint. The immune system recognises this component and elicits a reaction, which includes antibody production and memory cells.
This makes it possible for the body to become immune without actually getting the disease.
A vaccine is a safe version of a pathogen or one of its components that is introduced to a person. This may include a weakened or inactive pathogen, a specific protein, or genetic instructions such as an mRNA blueprint. The immune system recognises this component and elicits a reaction, which includes antibody production and memory cells.
This makes it possible for the body to become immune without actually getting the disease.
How Long It Lasts
Active immunity is usually persistent, due to the development of immune memory. Memory cells can remain in the body for years, decades, or, in some cases, a lifetime.
However, the duration of protection varies depending on the pathogen and the immune response. Some pathogens change over time, which can reduce existing protection. Therefore, certain diseases may require booster vaccinations to maintain effective immunity.
However, the duration of protection varies depending on the pathogen and the immune response. Some pathogens change over time, which can reduce existing protection. Therefore, certain diseases may require booster vaccinations to maintain effective immunity.
Examples
There are two types of active immunity, based on the way the body comes into contact with the pathogen. They are:
Natural Active Immunity (Through Infection):
Natural Active Immunity (Through Infection):
- Chickenpox: Recovering from chickenpox can provide lasting protection against future infection.
- Measles (or Mumps / Rubella): Recovering from a viral infection like measles stimulates a robust immune response, leaving behind long-lasting memory cells that usually protect against re-infection for a lifetime.
- Common Cold Viruses: Recovery from a cold can lead to antibodies against specific viruses, although protection may be temporary.
- Polio Vaccine: The polio vaccine stimulates the immune system to develop antibodies against polio virus.
- MMR Vaccine: The MMR vaccine is a combination vaccine that provides protection against the diseases of measles, mumps and rubella. One must get two doses of the vaccine for best protection against the diseases.
- Hepatitis B Vaccine: This vaccine stimulates targeted immune defences against the Hepatitis B virus.
What is Passive Immunity?
Passive immunity forms when a person is given antibodies made outside the body. These antibodies come from another person, an animal, or a lab.
Passive immunity is different from active immunity because the antibodies do not lead to the formation of memory cells.
This type of immunity helps in emergencies. It also helps when a person’s immune system cannot build its own response.
How Does Passive Immunity Work?
Passive immunity is the transfer of antibodies from the outside. Since the immune system does not need to identify the pathogen and produce antibodies itself, protection begins quickly.
These transferred antibodies react with particular antigens or toxins found on the pathogens or toxins. They can then neutralise the threat or assist the immune system in identifying and eliminating it.
These transferred antibodies react with particular antigens or toxins found on the pathogens or toxins. They can then neutralise the threat or assist the immune system in identifying and eliminating it.
Why is Passive Immunity Temporary?
Passive immunity is temporary because the recipient's body does not develop its own memory B cells or T cells against the pathogen. The transferred antibodies are gradually broken down and removed from the body.
Once these antibodies decrease to ineffective levels, the protection they provide also fades.
Once these antibodies decrease to ineffective levels, the protection they provide also fades.
When is Passive Immunity Most Useful?
Passive immunity may be useful in certain situations where active immunity is not available. It can also be possible when there is not sufficient time for active immunity to develop.
Here are a few situations when passive immunity can be useful:
Here are a few situations when passive immunity can be useful:
- Emergency Post-Exposure Prophylaxis: It can offer immediate immunity against severe diseases like rabies or some venomous bites.
- Immuno-compromised Individuals: May benefit immuno-compromised individuals who are unable to achieve adequate immunity only via vaccination.
- Newborn Protection: Maternal antibodies can provide infants with temporary protection while their immune systems are still developing.
How Long It Lasts
Passive immunity generally lasts for a few weeks to several months. Its duration depends on factors such as the amount and source of antibodies transferred and how quickly the body breaks them down.
Examples
Passive immunity may be natural or via medical treatment. Here are some common examples of passive immunity:
Natural Passive Immunity:
Natural Passive Immunity:
- Placental Transfer: Maternal antibodies, especially Immunoglobulin G (IgG), can cross the placenta to give protection to the developing fetus.
- Breast Milk / Colostrum: Antibodies, especially Immunoglobulin A (IgA), in the breast milk help to protect the infant's gastrointestinal system from some pathogens.
- Antivenoms: These are antibody-based medications that are used following a venomous animal attack, like a snake or spider.
- Immuno Globulin Replacement Therapies: Immunoglobulin (antibody) replacement therapy (IRT) is an effective and commonly used treatment for people with inborn errors of immunity (IEI), such as primary immunodeficiencies (PID).
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Key Differences Between Active and Passive Immunity
Active immunity vs passive immunity describes two different ways the body protects itself from infection. Active immunity occurs when the immune system produces its own antibodies after vaccination or exposure to a pathogen, leading to long-term protection.
Passive immunity provides ready-made antibodies for quick protection, but it is short-term and does not create immune memory.
| Feature | Active Immunity | Passive Immunity |
|---|---|---|
| Source of antibodies | Internal production by the person’s immune system. | Introduced via external sources such as vaccines. |
| Speed of protection | Slower (can take days or weeks to develop) | Provides immediate protection |
| Duration of protection | Long-lasting; often lifelong | Short-term (weeks to months) |
| Memory cells formed? | Yes | No |
| Risk of mild side effects | Possible (e.g., mild fever after vaccination) | Minimal |
| Best used for | Long-term prevention | Immediate or emergency protection |
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Active Immunity: Advantages and Limitations
Active immunity helps the body build its own defense system after vaccination or infection, giving long-lasting protection. It is very effective in preventing many diseases. However, it takes time to develop because the immune system must first respond and produce antibodies. It may also cause mild side effects after vaccination or exposure.
| Advantages | Disadvantages |
|---|---|
| The protection gained from active immunity is lifelong and provides continuous protection against specific diseases. | The process of development is long and can take a while, so the body can take days or weeks to respond fully. |
| Active immunity creates immunological memory to protect against future re-exposure and quick responses. | It is not ideal for quick protection, so if the pathogen exposure has already happened, active immunity cannot help them. |
| Active immunity is built through natural infections or can be introduced via a vaccine. | Individuals with a weaker immune system may not be able to develop a strong and active immunity even with the help of vaccination. |
| Active immunity helps create herd immunity, which can help stop the spread of infections among a population. | After administration, some vaccines require booster shots, as their effect can weaken over time. |
| Active immunity can become a cost-effective solution, as it can be provided widely through national vaccination programmes. | After the vaccine is given, there can be mild side effects such as fever, fatigue or soreness. |
Passive Immunity: Advantages and Limitations
Passive immunity provides immediate protection by giving the body ready-made antibodies. It is useful in emergencies and can quickly fight infections or toxins.
However, this protection is short-lived because the body does not produce its own antibodies or memory cells. It also does not provide long-term immunity against future infections.
| Advantages | Disadvantages |
|---|---|
| Passive immunity offers quick protection and is ideally given in cases of emergencies such as snake bites, rabies exposure or immune conditions. | The protection is temporary, and the antibodies can break down over weeks to months without forming any memory cells. |
| Newborns are also protected by passive immunity because they lack a developed immune system. | These antibodies do not train or affect the immune system, so future exposure still requires medical help, as the immune system cannot fight it alone. |
| Those who are sick or possess an inactive immune system due to illnesses or medication also benefit from passive immunity. | Providing it repeatedly can be expensive or difficult in case of specific illnesses. |
| This immunity can be a lifesaver when waiting for the immune system to fight the infection is not an option. | Some individuals may get serum sickness or allergic reactions. |
Conclusion
The human body and modern medicine have grown to depend on active and passive immunity. Active immunity is either acquired naturally or through active vaccination programmes.
It provides long-term and durable protection against pathogens by training the immune system. Passive immunity provides quick protection and people use it in emergencies. People also use it early in life, when innate immunity is weaker.
These immunity types show why active and passive vaccination matter. They remain among the most powerful tools to protect personal and public health. It can come from a childhood vaccine.
It can also be a lifelong defence mechanism. Maternal antibodies can protect a baby early on.
Frequently Asked Questions (FAQs)
Explain the difference between active immunity and passive immunity.
Active immunity is the immunity the body makes after exposure to infections through vaccines or infection. The immunity developed after introducing antibodies through injections is passive immunity.
What are examples of active immunity?
A few of the examples include the development of immunity after recovery from diseases such as measles. Vaccines for different diseases can also help the body gain immunity by activating the immune system.
What are examples of passive immunity?
Passive immunity can come from antibodies in a mother’s milk or through the placenta. It can also come from antivenom injections given to snake bite patients.
Which lasts longer, active or passive immunity?
Active immunity lasts longer, as it spans from several years to a lifetime. It involves the formation of memory cells.
Passive immunity is short-term. It helps fight disease for weeks or months. It does not form memory cells.
Passive immunity is short-term. It helps fight disease for weeks or months. It does not form memory cells.
How are active and passive immunity used in vaccination?
Vaccines help the body build active immunity by causing the immune system to make antibodies and memory cells. This gives long-term protection against disease.
Passive immunity helps the body respond in emergencies like snake bites. It provides immediate protection, but it does not last long.
Passive immunity helps the body respond in emergencies like snake bites. It provides immediate protection, but it does not last long.
Why is active immunity important for children?
Humans build active immunity through vaccines in childhood for measles, polio, diphtheria and whooping cough. It helps children build long-term protection during their developmental years and helps build herd immunity.
How does passive immunity help in emergencies?
In emergencies like snake bites or rabies exposure, the body cannot make antibodies fast enough. Passive immunity can provide immediate and ready-made antibodies to neutralise the toxins or pathogens.
What is the difference between passive and active immunization?
Active immunization makes the body produce its own antibodies using vaccines or exposure to pathogens. It builds long-term protection.
Passive immunity gives ready-made antibodies for quick protection. It works fast but lasts only a short time and does not form memory cells.
Passive immunity gives ready-made antibodies for quick protection. It works fast but lasts only a short time and does not form memory cells.
Which vaccine provides passive immunity?
Standard vaccines do not create passive immunity. They train the immune system to build active immunity.
Passive immunity comes from antibody treatments like antiserum or special injections. These contain ready-made antibodies for specific exposures.
Passive immunity comes from antibody treatments like antiserum or special injections. These contain ready-made antibodies for specific exposures.
Does passive immunity develop into active immunity?
No, passive immunity does not develop into active immunity because they are separate forms of immune protection. Passive immunity is the 'borrowed antibodies' form of immunity that gives temporary protection. On the other hand, active immunity is the body's own immune response.
Why choose vaccines over natural infection?
Vaccination creates a controlled and predictable immune response that establishes long-term immunity without the risk of severe illness. On the other hand, natural infection is exposure to live (replicating) pathogens and can lead to severe infections, organ damage, or death.
Can active and passive immunity occur simultaneously?
Yes, active and passive immunity can occur simultaneously, which is known as simultaneous active and passive immunisation. This approach provides immediate protection through external antibodies while also helping the body develop long-lasting, self-generated immunity.
For example, let us consider that a rabid dog bites a person. After that, the patient gets passive immunoglobulin and active vaccine which prevent the infection from spreading.
For example, let us consider that a rabid dog bites a person. After that, the patient gets passive immunoglobulin and active vaccine which prevent the infection from spreading.
What is the difference between the primary and secondary immune responses?
The primary immune response occurs when the body encounters germs for the first time. It is usually slower and weaker because the immune system needs time to recognise them and produce specific antibodies. In contrast, the secondary immune response occurs after a previous exposure to the same germs. It is faster and stronger because memory cells remember them and quickly activate the immune response.
ARN: May26BG/150526/KB
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