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What Is Natural Immunity?

Medically Reviewed by Neha Pathak, MD on November 17, 2021

Your immune system defends your body against infections and illnesses. It makes proteins called antibodies that counteract or kill germs, like viruses and bacteria. You get protection, or “immunity,” from a specific disease when your immune system makes an antibody for it.

Natural immunity happens after you get infected by a germ and your immune system responds by making antibodies to it. The infection could make you sick. But if you’re exposed to that germ in the future, your body’s defenses spot it and fight back with antibodies. This makes you less likely to get infected again.

How Long Does Natural Immunity Last?

Natural immunity to a disease can weaken over time, though. How quickly or slowly this happens depends on the disease.

For example, if someone gets natural immunity from a COVID-19 infection, the immunity may fade after 3 months. On the other hand, a child who gets measles is unlikely to ever catch it again.

Here’s a look at the different types of immunity, including the differences between natural and vaccine-induced immunity, and how they compare against COVID-19.

What Is Vaccine-Induced Immunity?

Vaccines can protect your immune system against diseases without making you sick.

They safely boost your immunity by using a killed or weakened version of a germ to teach your body’s defenses to fight back against the real thing. Even though they can bring on side effects, they rarely make someone seriously ill.

Many vaccines can cause side effects like:

But side effects like these don’t mean you’re sick or that you got an infection.

Severe vaccine side effects are rare. In most cases, the benefits of getting vaccinated against a disease far outweigh the risks.

Is Natural Immunity Better Than a Vaccine?

While it’s true that natural active immunity can make you immune to a disease after just a single case of infection, there is a downside: You have to get sick. And many illnesses can cause serious health issues that can affect you, sometimes for life.

For example, in some people, chickenpox can cause lung infections (pneumonia), blood infections (sepsis), and swelling of the brain (encephalitis). Before a vaccine was developed, this common childhood illness resulted in 10,000 hospitalizations every year.

You can avoid risks like these by getting all the vaccines your doctor recommends.

What Is Active Immunity?

Vaccine-induced immunity and natural immunity are both types of active immunity. That’s the medical term for when you’re exposed to something that spurs your immune system to make antibodies to a disease.

Depending on the disease, both naturally acquired natural immunity and the vaccine-induced type can last for a long time.

What Is Passive Immunity?

This is the other main type of immunity. Instead of your body making antibodies, you get passive immunity by receiving antibodies from another source.

This can happen in a couple of ways. A newborn gets passive immunity from their mother through the placenta, a structure in the womb that gives the baby oxygen and nutrients. You can also get passive immunity from treatments that have antibodies in them. You might need this type of treatment right away if a certain disease makes you sick. Doctors don’t recommend it for routine use.

Passive immunity provides germ-fighting power right away, whereas it can take weeks for you to build up active immunity. But in general, passive immunity doesn’t last as long.

What Is Herd Immunity?

It’s when a contagious disease stops spreading easily because enough people in the community (or “herd”) have become immune to it. This can be because of natural active immunity, vaccine-induced immunity, or passive immunity.

Vaccines aim to safely create herd immunity against infectious diseases by limiting the number of people who can spread the infection. But lots of people need to get vaccinated to help protect those who can’t for medical or other reasons.

For example, before the vaccine for smallpox was available, the disease used to kill millions of a people each year. Today, mass vaccination has basically rid the world of smallpox.

COVID: Natural vs. Vaccine Immunity

Some people who haven’t gotten vaccinated against COVID-19 worry about the safety of the vaccines and say they’d prefer to get natural immunity. But there are several dangers to doing that.

If you’re not vaccinated, there’s a much bigger chance that the virus could make you seriously sick or kill you. There’s no way to know whether the disease will be mild or severe. You also risk spreading it to other people, including loved ones. What’s more, you may be twice as likely to get re-infected by the virus, compared to someone caught COVID-19 while fully vaccinated.

If you catch COVID-19, research suggests that the natural immunity you get from it makes another COVID infection unlikely for 90 days. Experts aren’t sure just how long that level of protection lasts, though. But even if you’ve had COVID, you can be infected again: A recent study showed that people who’d had it but weren’t vaccinated were more than twice as likely to get it again, compared to vaccinated people who got a breakthrough case.

Getting fully vaccinated also gives you months of immunity -- without making you sick from the coronavirus. The vaccines are safe and effective. Even though they become less effective over time, they can still help protect you from getting severely ill from a breakthrough infection.

If you get two doses of an mRNA vaccine (like the ones from Pfizer or Moderna), you won’t need a booster shot for at least 6 months. If you get the Johnson & Johnson vaccine, you won’t need a booster shot for at least 2 months.

Show Sources

SOURCES:

CDC: “COVID-19 Vaccine Booster Shots,” “Myths and Facts about COVID-19 Vaccines,” “Immunity Types,” “New CDC Study: Vaccination Offers Higher Protection than Previous COVID-19 Infection,” “Chickenpox Vaccine Saves Lives and Prevents Serious Illness Infographic,” “Chickenpox (Varicella).”

Children’s Hospital of Philadelphia: “Vaccine Safety: Immune System and Health.”

Medscape: “As Vaccines Wane, Immune System Still Has Weapons Against Delta.”

UpToDate: “Patient education: Vaccines for adults (Beyond the Basics).”

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