How Does the Immune System Fight COVID-19?
GOOD RX HEALTH / ALYSSA BILLINGSLEY, PHARMD
One of the keys to combating COVID-19 is understanding how our immune system responds to SARS-CoV-2, the virus that causes the disease. We can potentially use this information for a number of purposes, like trying to predict the likelihood of severe illness, preventing or treating serious complications, developing a vaccine, and understanding if reinfection is possible.
Here, we’ll review what a normal immune response looks like, and what we’ve learned so far about how the immune system reacts to COVID-19.
How does the body usually fight off viruses? Let’s start with the basics of how your body responds to and fights off a virus. Our body’s immune response is broken down into two systems that work together in different ways to protect us: the innate and adaptive (or acquired) immune systems.
Innate immune system Your innate immune system is the first line of defense against viruses, taking minutes to hours to kick in. It provides a general defense against invaders. This system includes physical barriers like skin and protective layers in our throat or gut, chemicals in our blood, and different immune cells to fight infections. The main purpose of this response is to stop the spread of the virus throughout the body.
Adaptive immune system While this is going on, your adaptive immune system starts developing antibodies and white blood cells to both attack and remember the virus, making it easier to fight it again. Compared to your innate immune response, this response is more specific for the virus.
Your adaptive immune response is also slower, usually taking days to weeks. This is why even though you might be infected with SARS-CoV-2, it can take days to a few weeks for your blood to show antibodies for the virus and for you to start getting better. As part of this response, your body creates B cells, which are white blood cells made by your bone marrow. These cells make antibodies that turn on your immune system against the invader. These antibodies are specific to the virus and will bind to it, tagging it to be destroyed by other immune cells.
Some B cells work to fight the current infection, while others are stored in the body as a memory of the virus to fight future infections, sometimes lasting for decades. This is generally how many vaccines work. They use your adaptive immune system to create long-lasting memory cells. For example, memory B cells you develop from getting the smallpox vaccine can last over 50 years. However, some vaccines may require multiple doses to get an adequate immune response, and some require boosters as the initial protection starts to wear off.
T cells are also white blood cells that are part of your adaptive immune system. Some T cells stimulate B cells to make antibodies, while others kill cells that have been infected by the virus. On top of that, these cells use molecules called cytokines to act as messengers to the rest of the immune system. Cytokines are produced by some of the immune cells in our innate immune response as well.
As a part of both the innate and adaptive immune responses, cytokines can play a large role in the development of severe COVID-19. More on this next.
How does the immune system respond to COVID-19?
Researchers have been trying to understand why some people get sick from COVID-19 while others do not. Looking at how the immune system responds to the virus can give us some idea, and it can possibly help us try to predict the course of the disease in people who have been infected.
Under normal circumstances, the innate immune response kicks in first to attack and clear out the virus, followed by the adaptive immune response to remove any remaining virus and create a memory for future infections. For people with asymptomatic or mild cases of COVID-19, everything tends to work together as it should, or at least it does not progress to severe disease that requires hospitalization. But in severe cases, especially with older people, research has suggested that sometimes the different arms of the immune response can be out of sync. This can create a perfect storm, leading to some of the complications that we’ve seen in severe COVID-19 cases that become critical.
What can go wrong with severe COVID-19 In people with severe disease, certain parts of the immune response ramp up too much while those involved in clearing the virus don’t work as well. In other words, the immune system continues to send in reinforcements but fails to control the disease. This can progress into what is often described as a “cytokine storm.” During a cytokine storm, your immune system becomes hyperactive. Cytokines involved with inflammation (which is normally used to help clear an infection) may increase dramatically. This can cause inflammation to go haywire and spread around the body, with the potential to disrupt each of its vital functions.
The end result of this exaggerated inflammation can include critical damage to organs like the lungs, kidneys, and heart, a risk of blood clots in places like the lungs (pulmonary embolism) or the brain (stroke), and septic shock where your blood pressure drops to dangerously low levels. Your lungs may fill up with fluid, and multiple organs can fail.
It is believed that people with severe disease that experience cytokine storm generally will have a worse prognosis and higher risk of death from COVID-19. Who is at risk for developing a cytokine storm?
While we are still learning about the risk factors for severe COVID-19, it makes sense that having underlying conditions that are associated with inflammation or a weakened immune system can lay the groundwork for normal processes in the body to not work as they should. This can include, but is not limited to:
High blood pressure
Chronic obstructive pulmonary disease (COPD)
Older age can also put you at risk, since the immune system typically does not work as well as we get older. Race can play a role, too. It is thought that Black people may be more likelyto experience a harsher immune response, leading to a severe cytokine storm.
Once you’ve had COVID-19, are you immune to the virus? We’re not sure whether or not our immune systems have a strong enough response to the virus after an infection to make enough antibodies, or if those antibodies stick around long enough for immunity. The amount of antibodies that can be measured in your blood may also depend on the amount of virus you were exposed to and the severity of your infection.
However, antibodies don’t seem to be the only factor in developing immunity after COVID-19, as researchers believe that memory cells may play a large role as well. The good news is that results from vaccine clinical trials are promising, with candidates showing a good immune response to the virus. Currently, there are several vaccine candidates entering phase 3 clinical trials, which means they are being tested for safety in a large group of people.
And while there are no approved treatments for COVID-19 yet, several therapies are being studied, including those that attack the virus, calm down the hyperactive immune response, or use antibodies to treat or prevent an infection.
What are some ways to boost your immune system? While there are no proven ways to prevent COVID-19, here are some healthy lifestyle habits that you can use to keep your immune system as strong as possible.
Get enough sleep Studies have shown that getting enough sleep is important for our immune system. Much like how we have a rhythm of being sleep and awake, the different parts of our immune system seem to follow this rhythm as well. If you are regularly not getting enough sleep, this can also put stress on your body, causing inflammation. So how much sleep do you need? The Centers for Disease Control and Preventionrecommends that adults should get at least 7 hours of sleep or more each night.
Eat a healthy diet Nutrition supports our immune system, too, making sure that it has the energy and nutrients that it needs to fight off an infection. In fact, important parts of our immune health can be found in our gut, including immune cells and microorganisms like good bacteria that keep things in balance. The World Health Organization recommends eating fresh and unprocessed foods every day, drinking 8 to 10 cups of water daily, eating moderate amounts of fat and oil, and eating less salt and sugar.
Exercise Regular physical activity can help improve your immune system’s defenses by bolstering your immune cells and reducing inflammation. Try to get daily exercise, ideally up to 60 minutes of moderate activity. This includes activities like walking, running, or cycling. If your ability to exercise is limited due to disability or health conditions, just moving around more can be helpful (or as recommended by your provider). Keeping active, as well as eating a healthy diet, can help you maintain a healthy weight that can also lower your risk of severe disease.
Quit smoking Smoking has a negative effect on your immune system, making you more susceptible to infections and increasing your risk of severe COVID-19. While some people use electronic cigarettes as an alternative to regular cigarettes, they can potentially increase inflammationin the lungs. If you currently smoke or vape, it is recommended that you consider quitting.