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How Does a Vaccine Work? This Is What You Need to Know

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In this era of COVID-19, millions of people are planning their lives and futures around the hope of a vaccine. In the meantime, experts are urging people to take their regular flu shots to prevent a “twindemic.”

But how does a vaccine work, and why do we need a flu shot every year? You don’t have to stay in the dark about this. Once you understand some basics about the body’s immune response, it’ll be much easier to see why and how vaccines can make you immune to certain viruses and bacteria.

Got questions? You’re not alone. We’ll walk you through what you need to know:

Antibodies and Immunity

To understand how vaccines work, we first have to understand the body creates an immune response. In fact, the immunity we get from vaccines is an imitation of what goes on naturally in the body when we fight off disease. It’s the reason we usually won’t get the same illness twice. Here’s how the body does it:

1. Invasion of the Virus or Bacteria

When a virus or bacteria enters your body, it will attack your healthy cells, which allows it to multiply and spread. This is the process of the germ becoming an infection.

2. Creating Antibodies

Your white blood cells, including macrophages, B-lymphocytes, and T-lymphocytes, are the ones that constitute your body’s immune response. Macrophages will “swallow” the germs, leaving behind pieces called antigens.

The other immune cells will respond to the presence of these antigens by creating antibodies to attack them.

3. Immunity Against the Virus or Bacteria

Your body “remembers” how to respond to this germ by using certain T-lymphocytes called memory cells. These cells remain in your body after the attack so your immune system can act quickly if it spots the same virus or bacteria again.

If it does, your body will produce antibodies to attack the germ before it spreads into an infection again. In short, you have a very low chance of getting sick from the same germ again. This is what’s called immunity.

Antigens and Vaccine Immunity

If you think about the way the body recognizes and attacks germs, you can see how it’d be nice if we could do the recognition part without the getting-sick part. Fortunately, this is exactly what vaccines are for.

But how do vaccines work?

Scientists create most vaccines by using dead or weakened versions of the germ in question. This means the vaccine will put antigens into your body to get the proper immune response, but the germ itself won’t be strong enough to overpower your body and make you sick.

Experts are also innovating new ways of inducing the right antibodies for immunity. For example, Kenneth Chien at Moderna is leading mRNA research for a new kind of vaccine.

In short, this is a way of getting a person’s body to create antibodies by using genetic code to “teach” the body’s protein-making components what to create. It’s one of the ideas that might give us a COVID-19 vaccine in the coming months.

How Does a Vaccine Work in Your Body?

You might have heard that a vaccine has the possibility to cause fever and other illness-type symptoms in the weeks after its administration. Does this mean you got sick?

Well, there are a few possibilities here. Most likely, you’re experiencing your body’s immune response to what it’s treating as an infection. Although the germ in the vaccine will be dead or weakened, your body might still react with a fever.

It’s also possible that you somehow contracted the illness from somewhere in your daily life before the vaccine took full effect. And then there’s the rare case of the vaccine itself causing harm, which we’ll cover in the next section:

Vaccine Safety

Are vaccines safe? It may seem like a risk to inject a bacteria or virus into our bodies, even if it’s dead or weakened.

The answer is, in most cases: yes. In fact, it’s safer for you—and the whole community, as you’ll see in the section on herd immunity—for you to get a vaccine than not.

The only time a doctor recommends against vaccines is when people have medical reasons why vaccines would be a larger risk for them. These are usually immune system issues, like autoimmune disorders.

Why Do We Need the Flu Vaccine Every Year?

At this point, you may be wondering why we would need a vaccine for the same illness year after year. After all, once someone is immunized from the flu, shouldn’t that immunity carry into the next year?

Well, yes and no.

In general, every year’s flu shot should make you immune to the strain of virus the vaccine was designed to target. And if that same virus were to come again the following year, you’d have a pretty good chance at resisting it.

But what we call ‘the flu’ is actually a collection of similar flu strains, mutating all the time to get past our bodies’ defenses. Scientists keep up by creating new versions of the flu vaccine every year, but each vaccine targets a slightly different strain.

Herd Immunity

From a public health perspective, a community is safest from a virus or bacteria when a critical percentage of people in the community are immune. And the best way to immunize lots of people at once is through vaccines.

Not everyone can get a vaccine. This includes immunocompromised individuals and newborns, as well as people getting chemotherapy and organ transplants. In order for them to receive the benefits of a vaccine, they’ll need to count on the people around them to get immunized.

Viruses and bacterial infections are spread from person to person. Every person who gets sick from the germ has the potential to spread it to several others. When you break these links by immunizing a certain percentage of people, you lower the chance of a non-immunized person even coming into contact with the germ.

Herd immunity is different for different infections. When the infection is more contagious—like COVID-19, for example—you’d need a higher percentage of immunizations for herd immunity.

Now You Know

Some people, from kids all the way to senior citizens, feel uncomfortable getting immunizations because they aren’t sure what they do. If you’ve got someone in your life who’s like this, take the initiative to talk to them about what vaccines really do. Next time someone asks, “How does a vaccine work?”, you’ll know what to say.

And for more tips on taking charge of your personal health, check out our other health-related articles!

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