MENU NEWSLETTERS SEARCH Health Topics Wellness Food & Eating News & Alerts Coronavirus / COVID-19 HEALTHY LIVING All About Immunity and the Immune System What It Is How It Works Vaccines Boosting Immunity Jump to More Topics By Becky Upham Medically Reviewed by Laura Martin, MD Reviewed: November 23, 2021 Medically Reviewed A strong immune system is key to your overall well-being.Adobe Stock A normally functioning immune system keeps us well by protecting the body’s healthy tissue and fighting off harmful foreign intruders such as bacteria and viruses. Although our immune system is finely tuned to protect us, there are ways to strengthen it with recommended vaccines and healthy habits. Keep reading to find out everything you need to know about how the immune system works, how vaccines help immunity, and what you can do to keep your immune system in tip-top shape. What Is the Immune System? Let’s start at the beginning: The immune system is the network of cells throughout our body (in the skin, the blood, and elsewhere) that work together to prevent or limit infection from potentially harmful pathogens and prevent damage from noninfectious agents (like sunburn and cancer). How the Immune System Works There are several components of the immune system, including the following: The skin can keep many germs from entering the body. Mucous membranes These are the moist inner linings of places such as the mouth, nose, and lungs that produce mucus and other substances that capture and combat germs. White blood cells The body produces these to fight infection and other diseases. Organs and tissues of the lymph system The thymus, spleen, tonsils, lymph nodes, lymph vessels, and bone marrow are the parts of the body that make, store, and carry white blood cells. Scientists categorize the various immune cells in two groups: innate immune cells and adaptive ones, says Michael N. Starnbach, PhD, a professor of microbiology at Harvard Medical School in Boston. When foreign invaders like bacteria or viruses enter your body, they multiply and attack, which can lead to infection, disease, and illness. Innate immune cells are the first line of defense against the invaders, says Dr. Starnbach. These include barriers such as the skin and mucus membranes that keep some pathogens from entering the body. The innate immune system also includes some cells and chemicals that identify microbes and other potential threats, triggering a response to get rid of them, says Starnbach. Adaptive immune cells are involved in the second part of an immune response. “These are special cells that respond to ‘mop up’ the remainder of the organisms left after the innate immune response,” he explains. Here comes the interesting part: The adaptive immune system has what’s known as “immune memory,” meaning that when those cells see a pathogen that has previously entered the body, not only do they help get rid of the invader, they also make more copies of themselves to continue to build a stronger defense in the future so the body is better prepared to fight off the pathogen if and when it reappears, says Starnbach. This can happen even when you don’t get ill from the germs or virus. For example, exposure to the flu can still help strengthen your immune system, even if you don’t catch it, says Eili Klein, PhD, an associate professor of emergency medicine at Johns Hopkins Medicine in Baltimore and a fellow at the Center for Disease Dynamics, Economics, and Policy in Washington, DC. “That exposure helps your immune system make antibodies that ‘remember’ the virus and how to attack it,” he explains. That’s a big reason why an older adult is more vulnerable to infection than a younger adult — because there is a faster waning of their antibodies, he says. “That’s why older people are more likely to get the flu — their immune system doesn’t work as well,” says Dr. Klein. When a new virus appears, as was the case when SARS CoV-2 (the virus that causes COVID-19) first began to spread, no one had a heightened response to it, because no one’s immune memory had encountered it, says Starnbach. That left more of us susceptible to being infected, he adds. How Vaccines Work to Provide Immunity and Strengthen the Immune System Vaccination is one of most convenient and safest ways to prevent many diseases, according to the Centers for Disease Control and Prevention (CDC). A vaccine works with your body’s natural defenses to help you develop immunity to disease in a safe way, without your having to actually get sick. RELATED The Flu Shot: What You Need to Know Vaccines work because of immune memory, Starnbach says. When you get a vaccine, such as a flu shot, you’re exposing your immune system to a version of the virus that causes the body to enhance the number of immune cells that can respond to and fight off the virus if you get exposed to the real thing. Vaccines are a boost to our immune system that actually does work, Starnbach says. But it’s worth noting that a vaccine isn’t a boost to our whole immune system. A flu shot doesn’t make you more resistant to colds and other illness; it boosts your immune response to the specific strains of the flu that the vaccine was designed to protect you from. “A vaccine is very specific and designed to fight off a particular pathogen such as chicken pox, polio, or the flu,” Starnbach says. A new kind of vaccine emerged during the pandemic — messenger RNA vaccines, or mRNA vaccines — and they work differently from the vaccines that preceded them. Rather than using a version of the virus to get the body to be able to recognize and mount an immune response, the Pfizer-BioNTech and Moderna COVID-19 vaccines work by introducing a piece of mRNA that corresponds to a viral protein. The vaccine “teaches” cells how to make proteins that will trigger an immune response. Experts believe that mRNA technology will transform the way we treat and prevent many illnesses. There are currently trials underway testing the safety and efficacy of an mRNA flu vaccine. RELATED: Is an mRNA Flu Shot on the Way? How Vaccines Can Protect You Against Certain Diseases and Prevent Others Altogether The vaccination schedule to protect children from many serious (and sometimes deadly) diseases begins just a few months after they are born. DTaP, which immunizes children against diphtheria, tetanus, and whooping cough, is usually first administered at 2 months, notes the CDC. Polio, hepatitis, measles, mumps, varicella (chicken pox vaccine), and the flu are other diseases that children in the United States get vaccinated against. RELATED Everything You Need to Know About Vaccines, From Birth to Adulthood Although many of us associate vaccines and shots with babies and childhood, you need vaccines throughout your entire life span. The immunity you get from childhood vaccines may wear off over time, and your risk of certain diseases can increase as you grow older. The COVID-19 vaccine is approved and recommended for everyone 5 years old and older with very few exceptions. Widespread vaccination is considered essential to help stop the pandemic. There is emerging evidence that although the COVID-19 vaccine is effective in preventing severe disease, that effectiveness decreases over time. A booster shot, given to people who finished their initial series six months earlier, can provide an increased immune response, per the CDC. RELATED: What You Need to Know About COVID-19 Vaccines The CDC recommends that all adults (with very few exceptions) get the flu vaccine every year. Each year researchers use the most up-to-date information to decide what strains to include in the vaccine; most flu shots in the United States protect against three or four different flu viruses, according to the agency. All adults need to get the DTaP once if they didn’t receive it as an adolescent to protect against pertussis (whooping cough) and then a DT (diphtheria, tetanus) or DTaP booster shot every 10 years. It’s recommended that people age 50 and over get the shingles vaccine, which protects against shingles and complications related to the disease. Adults older than 65 should get the pneumococcal polysaccharide vaccine (PPSV23), which protects against serious pneumococcal disease, including meningitis and bloodstream infections. Although it’s the exception rather than the rule, there are some cases where an individual should not get certain vaccines that are recommended or required for most healthy people. This may be for reasons such as age, health conditions, or other factors. Usually, you’ll be aware of this because of conversations with your healthcare provider, but if you aren’t sure, check in with your doctor. What You Can Do to Boost Your Immune System Naturally Boosting your immune system globally — making yourself more resistant to anything that might be out there — may sound like a good idea, but that could mess up the balance of the immune response, Starnbach says. “Our immune systems are very finely tuned,” he explains. The different immune cells are geared to recognize things in our bodies that are potentially harmful and to clear out those things. Some researchers have investigated whether supplements with specific vitamins and nutrients protect against colds and viruses, but the data suggest that if supplements are helpful they may do more in the way of reducing the severity of an infection or illness once you catch it rather than preventing it in the first place. RELATED Why Proper Hand-Washing Is Essential During Cold and Flu Season So what can you do to protect yourself against the coronavirus and other germs? First of all, focus on preventing exposure to and the spread of pathogens, says Yufang Lin, MD, an integrative internal medicine doctor at Cleveland Clinic in Ohio. “Wash your hands, and if you cough or sneeze, do so into a tissue and throw that tissue away,” she says. The other part of the equation is to practice health-promoting behaviors that keep your own immune system functioning at its best (and that help prevent underlying chronic health problems that ultimately do make you more susceptible to infections), according to Dr. Lin and Starnbach. More specifically: Get enough sleep. Healthy sleep supports the immune system in a lot of really critical ways, Lin says. Research has found that very important parts of the immune response occur during the different stages and are regulated by our bodies’ circadian rhythms. Eat healthy foods. This includes lots of nutrient-rich fruits and vegetables. The vitamins and minerals in our food are the lifelines all the systems in our body rely on to function well (including the immune system); the better you feed the body with the nutrients you need, the better it runs and can avoid chronic and acute disease. Also avoid consuming excessive amounts of alcohol, which can interfere with immune function. RELATED: An Immunology Expert Shares What She Eats in Day Avoid environmental hazards. Prolonged exposure to toxic air pollution can have negative health effects, which can include damage to the immune system, according to the Environmental Protection Agency. Other toxins, which can include pesticides, heavy metals, and endocrine disruptors, impact immune system development, according to a research review published in the Journal of Immunology. Stay active. Researchers haven’t yet pinpointed the mechanism through which staying active keeps the immune system functioning best, but they do know exercise helps keep other systems in the body functioning properly, so they suspect there’s a link, notes MedlinePlus. A study published in Aging Cell found that older adults who exercise regularly can keep their immune systems functioning similarly to people decades younger who don't exercise regularly. Note: There's also evidence you can overdo it and that extreme training may harm immune function. For optimal immune function, stick with moderate activity levels. Manage your stress. Stress can suppress the immune system, keeping it from working at 100 percent. “Try to take time to relax and do something fun,” Lin says. “Make sure you take care of yourself.” EDITOR’S PICKS ON BOOSTING IMMUNITY 7 Foods That Fight Back: Immune System Boosters 8 Ways to Keep Your Immune System Healthy Why Exercise and Sleep Are Your Ultimate Defense Against Stress 10 Amazing Benefits of Exercise Autoimmune Diseases: What Happens When the Immune System Is Overactive In some people, the immune system is too active; it attacks the body’s own cells and tissues, says Starnbach. This is what happens in the case of autoimmune diseases such as rheumatoid arthritis and Crohn’s disease. Lupus is another example of an autoimmune disease. When people have lupus, the antibodies can’t distinguish between foreign invaders and the body’s own cells and tissues. The mistaken immune response can cause inflammation, which can contribute to arthritis, lupus rash, kidney damage, and other symptoms and health problems, according to the Lupus Foundation of America. Experts don’t know why autoimmune diseases occur; they aren’t contagious. There is a hereditary link for many autoimmune conditions, and it may be that a virus or an environmental factor triggers the disease if a person already has the genes for it. The symptoms of autoimmune diseases can come and go. When the immune system is acting up, it’s called a flare-up, and the symptoms get worse. Remission is when the symptoms improve or even disappear altogether. Factors That Can Weaken the Immune System What makes one person’s immune system “weaker” than someone else’s? There are several known factors that make it harder for our bodies’ immune systems to work at their best and fight off potentially harmful pathogens (like the new coronavirus). Here are some of them. Smoking Smoking suppresses your immune system and weakens your lungs, so people who smoke are more susceptible to pneumonia or a viral infection, Lin says. Medications Some drugs can keep your immune system from functioning the way a healthy person’s would, says Lin. “Immunomodulators, steroids, or medications for autoimmune conditions can suppress your immune system,” she says. Age Young children can be more susceptible to catching viruses because their immune systems are still developing; it’s part of the maturation process, Lin says. As they grow older, children’s immune systems are exposed to different viruses, they become accustomed to being exposed to more viruses, and they become much more able to fight those off. “But when they are very young, every time [children] see a new pathogen their body is mounting a significant response,” Lin says. Older people, too, tend to have weaker immune systems than other groups. Older people can have multiple chronic medical problems, says Lin. If the body is constantly dealing with a variety of medical conditions, that can make it harder to fight off a virus. “Along with that, as we get older our immune system gets a little bit weaker, and it can take longer for our bodies to mount a significant immune response when we get sick. That gives the virus or infection more time to grow or to replicate, which could lead to more severe symptoms,” says Lin. Underlying medical conditions Preexisting chronic medical conditions, like asthma, diabetes, and heart disease, can affect the immune system and put people with these conditions at higher risk of infections. Pregnancy Pregnant women experience changes in their immune system and body that may place them at higher risk of viral infections, says Lin. Just by being pregnant your immune system is somewhat stretched, because it is taking care of two rather than just one, she adds. Malnutrition People who are malnourished are more susceptible to viruses and certain diseases, Starnbach says. Deficiency in certain vitamins and minerals in the body keeps the immune system from functioning optimally. Replenishing those missing nutrients with supplements can help the immune system function in a healthy way and better ward off diseases and infections. But whether or not supplements help improve immune response generally or in specific ways in people who are not deficient in vitamins and nutrients is less clear. RELATED: Do Probiotics Help Your Immune System? Editorial Sources and Fact-Checking NEWSLETTERS Sign up for our Healthy Living Newsletter! Enter your email Subscribe By subscribing you agree to the Terms of Use and Privacy Policy. THE LATEST IN HEALTHY LIVING Plans For a Spooktacular Halloween? Here’s How to Stay Safe While Being Scary Expert tips on how to successfully avoid common Halloween hazards. By Becky Upham October 27, 2021 Research Links Common Synthetic Chemicals Found in Food Packaging, Cosmetics, and Toys to Early Death Phthalates may impact metabolism and contribute to inflammation in the body. How can you protect yourself? 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