What Does COVID-19 Do to Your Body, and How Does Your Immune System Fight the Virus?

When it works well, your immune system has many ways to tackle viruses like COVID-19. This natural defense is important in preventing severe illness from COVID. Your immune response also plays an important role in how well your body gets protection from the COVID vaccine.

Knowing what a normal immune response looks like can help you understand how your body might respond to a COVID infection.

How do you catch COVID?

COVID spreads through tiny particles that carry the virus. People release these particles when they breathe, talk, cough, or sneeze. The particles can hang in the air — especially indoors — and infect anyone who inhales them. You don’t have to be coughing or sneezing to spread the virus, and you don’t even have to feel sick. In fact, many people spread COVID before they even know they have it.

Most people catch COVID from being in close contact with someone who’s infected. But the virus can also spread in more subtle ways, like through poorly ventilated air or even shared indoor spaces. Surface spread (like touching a doorknob and then your face) is possible, but it’s a much less common route.

What happens to your body when you become infected with COVID?

When you get COVID, the virus doesn’t just stay in your nose or throat — it sets off a chain reaction throughout your entire body. Some people only feel like they have a cold. Others develop more serious symptoms. Here’s what’s happening behind the scenes:

• The virus enters your body through your nose, mouth, or eyes. It quickly attaches to cells in your airways and lungs and starts making copies of itself. This is the start of the infection.

• Your immune system fights back. As the virus spreads, your body activates its defenses. This causes early symptoms like fever, chills, body aches, and fatigue. For most people, the immune system clears the infection within a couple of weeks.

• Inflammation can cause more serious problems. In some cases, your immune response becomes too intense. The resulting inflammation can damage lung tissue and make it harder to breathe. This is especially true for people with underlying health conditions.

• COVID can affect more than just your lungs. Some people also have symptoms related to their heart, brain, digestive system, or blood vessels. This can lead to chest pain, confusion or “brain fog,” diarrhea, or blood clots.

• Symptoms can linger after the infection is gone. Long COVID refers to symptoms that last for weeks or months after the initial illness. These can include ongoing fatigue, trouble concentrating, or shortness of breath — even after you test negative.

How does the immune system respond to the COVID virus?

When you get infected with the COVID virus, your immune system kicks into gear with two layers of defense:

1. First, your innate immune system jumps in right away. This includes your skin, mucus, protective barriers in your airways, and immune cells. Together, they all work to stop the virus from spreading. If everything goes well, your body can handle the infection.

2. If that doesn’t do the trick, your acquired immune system gets to work. It takes a bit longer (days to weeks), but it creates a more targeted attack. This part of your immune system makes antibodies and memory cells that help fight off the virus. They also protect you from getting as sick if you’re ever exposed again. Vaccines train this part of your immune system to recognize COVID before you ever get infected.

In mild cases, both systems usually work in harmony. But in severe cases, parts of your immune response can become uncoordinated. Instead of helping, certain chemicals in your body, called cytokines, can cause too much inflammation throughout the body. This can lead to complications like blood clots, kidney injury, or even organ failure. This is often called a cytokine storm.

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How does a COVID vaccine affect your immune response?

The COVID vaccine is a critical part of your immune response to the infection. It activates your acquired immune system against the COVID virus.

This means that when you come in contact with the virus in the future, your body will have antibodies ready to fight and clear the infection. It can take multiple exposures for your body to create enough antibodies to fight COVID well. That’s why you need more than one vaccine to be fully protected.

But this protection doesn’t last forever. The COVID virus keeps changing itself, forming new variants. This allows it to go undetected by your immune system. Plus, the antibodies you create in response to the vaccine also decrease over time. These are the reasons why people need booster shots to rev up their immune system against COVID.

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Once you’ve had COVID, are you immune to the virus?

There’s evidence that after getting COVID, you do have at least some short-term protection against the virus. But most people can get reinfected later, especially with different variants of the virus. 

Immunity may last longer with some infections than others. For example, research suggests that infection with the Delta variant gave better protection than Omicron. The good news is that having immunity — whether from vaccines, infection, or both — can lower your risk of severe illness by up to 90% if you do get COVID again.

Keep in mind that the strength of your immunity likely depends on many factors, including: 

• Evolving strains of the virus

• The severity of your infection

• Your overall health status

• Your vaccine status

• Any underlying conditions that affect your immune function

Ways to boost your immune system

While there’s no guaranteed way to prevent COVID, you can support your immune health. Here are some tips to help keep your immune system as strong as possible:

• Get vaccinated. Vaccines are one of the best ways to boost your immunity against COVID. While they may not completely prevent you from getting a COVID infection, the vaccine can keep you from having a serious infection. It can also keep you from landing in the hospital or dying from COVID.

• Get enough sleep. Studies have shown that getting enough sleep is important for a healthy immune system. If you aren’t regularly getting enough sleep, this can stress your body, causing inflammation.

• Eat a balanced diet. Nutrition also supports your immune system, making sure that it has the energy and nutrients that it needs to fight off an infection. In fact, your gut hosts immune cells and microorganisms, like good bacteria, that keep things in balance.

• Get regular exercise. Regular physical activity can help improve your immune system’s defenses. Exercise has been shown to strengthen your immune cells and reduce inflammation.

• Quit smoking. Smoking has a negative effect on your immune system. It makes you more susceptible to infections and increases your risk of severe COVID.

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Written by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. A pulmonologist and hospitalist, she practiced and taught clinical medicine at hospitals in London for a decade before entering a career in health education and technology.

Reviewed by:

Farzon A. Nahvi, MD

Farzon Nahvi, MD, is an emergency medicine physician and author of “Code Gray: Death, Life, and Uncertainty in the ER.” He works at Concord Hospital in Concord, New Hampshire, and teaches at the Geisel School of Medicine at Dartmouth.

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