Natural Immunity

What is natural immunity?

Natural immunity is protection against a specific infectious disease that you gain after having that disease. When you get sick, your body’s immune system revs up and mounts an attack to rid your body of the invader — typically, a virus or bacteria. One way your body does this is by producing proteins called antibodies that target and destroy the invader. The antibodies clear out the infection and you feel better. But that’s just the first part of the story.

Once you feel better, you might not think much about what your immune system is up to. Yet, behind the scenes, tiny immune cells inside your body (memory cells) hold onto the memory of that infection. That’s because while they mounted their attack, they learned to recognize the antigen — or the chemical marker — associated with that specific invader, or germ.

These memory cells survive beyond the infection. They stick around with the sole purpose of patrolling for that same invader’s antigen. If the invader returns, your memory cells jump into action and alert other immune cells to swiftly attack and clear it out — often without you even noticing.

This process is a bit like finding an invasive weed in your garden. After you root it out, you remember what it looks like. This memory allows you to spot the weed and get rid of it even quicker if it grows back and threatens nearby plants.

Memory cells are a key part of how natural immunity works. But for your body to develop memory cells, it has to encounter the invader in the first place. So, natural immunity only develops once you’ve gotten the infection and recovered.

To understand the role natural immunity plays within your immune system, it helps to know a bit more about the different types of immunity and how they all work together to protect you.

Types of immunity

There are two main types of immunity, which serve as two lines of defense for your body:

• Innate immunity: Innate immunity is the first line of defense when an invader tries to get in. It includes anatomic barriers, like your skin and mucus membranes, as well as many different types of cells (like natural killer cells) that recognize invaders and immediately launch an attack. But these cells don’t remember the invaders after the battle is done. Instead, the cells launch the same attack every time regardless of the invader. Sometimes, this is enough to clear an infection. But if not, your innate immune cells call for reinforcements — your adaptive immune cells.
• Adaptive immunity: Adaptive immunity is a line of defense that recognizes, targets and remembers specific invaders. Specialized cells — including T-cells and B-cells — work together to recognize antigens that don’t belong in your body and destroy them. Memory cells in particular are heroes in this scenario because they’ve survived previous infections and can quickly respond to clear out subsequent infections.

When most people talk about natural immunity, they’re referring to a form of adaptive immunity. Your immune system naturally makes proteins and antibodies that target specific invaders and “remember” those invaders. This process prepares your body to recognize and eliminate the invaders in the future.

What is natural active immunity?

Natural active immunity is protection you receive from antibodies your immune system creates in response to an infection. This is slightly different from vaccine-induced active immunity, or protection you receive from antibodies your immune system creates in response to substances (like pieces of viruses or bacteria) in some vaccines.

What is natural passive immunity?

Natural passive immunity is protection that transfers from parent to child during pregnancy or nursing. For example, if you’re pregnant, you pass many types of antibodies to the fetus through the placenta. After your baby is born, if you breastfeed (chestfeed), you pass some types of antibodies to your baby through the milk. This antibody transfer allows your baby to gain protection against harmful germs before their immune system is ready to create all those antibodies on its own.

You can get passive immunity through artificial means. This involves getting an injection of antibodies to serve a specific medical purpose. For example, monoclonal antibodies and polyclonal antibodies help treat a wide range of medical conditions. In these situations, scientists make the antibodies in a lab or obtain them from animal sources.

How long does natural immunity last?

How long you’re protected from an infectious disease varies according to the disease. It also depends on your overall health, including whether you have a weakened immune system.

Sometimes, having an infection just once is enough to give you lifelong natural immunity. Examples of such “one-and-done” diseases include measles and hepatitis A.

Other times, your body generates natural immunity that protects you for a limited amount of time. This is why you can get some infections — like a common cold, COVID-19 and the flu — multiple times throughout your life. Your natural immunity is for a specific strain of the virus. But the viruses keep changing to work around our defenses.

Natural immunity vs. vaccination — what’s the difference?

Natural immunity and vaccine-induced immunity are both forms of active immunization. In both cases, your immune system creates antibodies and T-cells. But they’re making them in response to different triggers, or substances that spur your immune cells into action.

Germs (microbes) from an infection prompt your body to develop natural immunity. Substances in vaccines — like weakened microbes or proteins or mRNA — create vaccine-induced immunity.

When a large number of people gain immunity to a specific infectious disease naturally and/or through vaccination, we can reach what researchers call herd immunity. This is when an infection stops spreading because most people are immune to it. Vaccination is the safest way to reach herd immunity.

How can I boost my immune system naturally?

There’s a lot you can do to strengthen your immune system and help it work at its best. From getting enough sleep to eating foods rich in immune-boosting nutrients, you can help your immune system ward off viruses and other germs that could make you sick.

What is COVID-19 natural immunity?

COVID-19 natural immunity is protection against future infections that your body develops after recovering from a COVID-19 infection. The infection trains your immune system to recognize and destroy the virus that causes COVID-19 if it enters your body again.

Infectious disease experts emphasize you shouldn’t rely on natural immunity to protect you and your family. Instead, follow your healthcare provider’s recommendations for COVID-19 vaccination. Here’s why:

• COVID-19 is an unpredictable infection. You can’t always know how the virus will affect your body, how sick you’ll get or what long-term effects (like long COVID) you’ll end up with. Some research shows a COVID-19 infection causes your body to create autoantibodies. These are antibodies that attack your body’s own healthy cells, potentially leading to autoimmune disease. On the other hand, vaccination gives you predictable, safer and reliable protection. Any side effects are temporary and don’t cause lasting harm. Research shows no link between vaccination and the creation of autoantibodies.
• COVID-19 natural immunity changes as the virus mutates. When a virus mutates, it creates a variant, or a new form of the virus. That’s why natural immunity from one COVID variant doesn’t guarantee immunity from all variants. Research has shown earlier variants — up through delta — gave people strong, long-lasting natural immunity for many months after infection. Omicron and its subvariants still give you natural immunity, but it may not be as strong or durable. That’s because these newer variants — currently the only ones circulating — have “high immune escape.” This means they’re sneaky and can more easily dodge your body’s natural immune defenses. The vaccines are updated every year to fight the most current strain of COVID.

Instead of relying on natural immunity for protection, talk to your provider about the COVID-19 vaccine. Vaccination provides your body with a powerful form of active immunity without risking severe illness, hospitalization or death from an actual infection. Healthcare providers advise you to still get vaccinated even if you’ve had COVID-19.

How long does natural immunity to COVID-19 last?

It depends. Many people gain protection against another infection (reinfection) for several months. But this natural immunity lessens as time passes. If you have a weakened immune system, your body may not build up effective natural immunity after an infection. So, you may get sick again sooner than others would.

In general, natural immunity from a COVID-19 infection may offer strong protection against severe illness and hospitalization. You might still get COVID-19 during that time, but the infection likely won’t be as severe. We’ll continue to learn more as researchers study the latest variants and reinfection trends.

Keep in mind that having COVID-19 won’t protect you against other viruses going around, like flu or RSV, or common bacterial infections like strep throat. A different germ (microbe) causes each type of infection. So, even if you have some short-term natural immunity against COVID-19, it’s a good idea to keep taking precautions to protect yourself and your family from all harmful germs. Tips include washing your hands often, wearing masks in certain social situations and avoiding others who are sick.

To get advice tailored to your needs, you should talk to a healthcare provider who knows you and your medical history. They can advise you on what you can expect after a COVID-19 infection and how to protect yourself.