Active vs. Passive Immunity: What’s the Difference?
Jake Newby
| 4 min read
Our bodies develop immunity against disease in different ways. When we contract relatively mild illnesses like chickenpox and the measles – typically as children – we usually develop natural, lifelong immunity against them after infection activates our immune systems.
Getting vaccinated against more serious diseases like COVID-19 and influenza (the flu) is another way to become actively immune to a disease. It’s uncommon for people to naturally develop long-lasting immunity against diseases like these, so getting vaccinated multiple times against them helps soften the virus’ strength. Passive immunity occurs when a person receives antibodies from someone else. Passive immunity does not require previous exposure to a disease agent – either through infection or vaccination – like active immunity does.
Here is a further breakdown of these two forms of immunity.
Natural active immunity
When we breathe in new air, eat new food or touch unfamiliar things, the natural, active immunity in our bodies usually springs into action. The active immune response can take days or even weeks to develop. Once it does develop, it’s long-lasting – sometimes even lifelong.
Vaccine-induced active immunity
Also known as artificial active immunity, vaccine-induced immunity gives our bodies a controlled way to create an immune response. When a weakened or dead form of a disease organism is injected into our bodies or administered via the mouth or as a nasal spray, that’s vaccine-induced immunity. Examples include:
- The COVID-19 vaccine
- The flu vaccine
COVID-19 vaccines are the safest way to build immunity against COVID because they cause a strong immune response. Getting the COVID-19 vaccine gives a high level of protection against the disease while providing an added layer of protection for those who have already had it. When we are vaccinated against COVID we typically have a higher initial immune response and a longer immune memory than unvaccinated people who have recovered from COVID-19 and developed a semblance of natural immunity.
The flu can be serious among young children, older adults and people with certain chronic health conditions like asthma, heart disease or diabetes, according to the Centers for Disease Control and Prevention (CDC). That’s why getting vaccinated is a safer choice than risking illness to gain immune protection.
A drawback to active immunity is that it doesn’t protect us against mutations of diseases that the body already has antibodies to, so when diseases mutate, they change structure in ways that our immune systems can’t recognize.
Passive Immunity
Passive immunity occurs when a person is given antibodies to a disease rather than producing them through their own immune systems. Passive immunity does not require previous exposure to a disease agent – either through infection or vaccination – like active immunity does. An example of passive immunity is when a baby acquires maternal antibodies transferred through its mother’s breastmilk or placenta. Another example of passive immunity occurs when people are treated with antibody-containing blood products, such as immune globulin. Immune globulin shots are designed to provide temporary, but swift protection against diseases like:
- Hepatitis
- Rabies
- Tetanus
The difference between active and passive immunity
Unlike active immunity, passive immunity provides immediate protection. But that protection is generally short-lived, as the supply of antibodies is not being replenished like they would be in someone whose own immune system was generating them.
If you’re wondering why vaccine-induced immunity is considered a form of active immunity, while immune globulin shots are passive, it is because immune globulin is a substance made up of antibodies that are naturally made by the body to provide protection from certain diseases. A vaccine is made up of actual viruses or bacteria that stimulate the body to make more antibodies. So, in the case of vaccines, your body still doing the heavy lifting. Your immune system treats the viruses and bacteria like any other exposure and begins actively fighting it. We rely on active and passive immunity to contribute to a well-equipped and strong immune system.
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Photo credit: Getty Images
