Why Do We Need Vaccines?

When we encounter harmful germs (bacteria or viruses), they can cause serious illness. Vaccines prepare your immune system to respond before an infection takes hold. They can prevent illness entirely or reduce how severe it becomes. The benefits go beyond individual protection – they also help keep communities safe.

This is known as herd immunity. When enough people are vaccinated, germs have a harder time spreading. This helps protect those who can’t be vaccinated, like newborns or people with certain health conditions.

How Do Vaccines Work?

Your immune system is your body's defense against germs like bacteria and viruses. It uses white blood cells as tiny soldiers to identify, attack, and remember threats.

There are special types of white blood cells: macrophages, B-cells, and T-cells.

• Macrophages find and destroy germs and leave behind pieces called antigens.
• B-cells spot these antigens and make antibodies, which help fight the germs.
• T-cells help destroy germs, too.
• Some B-cells and T-cells become "memory cells," which remember germs they have fought before, so your body can fight them faster next time.

Vaccines train your immune system using a safe version of a germ – either a tiny piece or a weakened version so your body can practice fighting them. This way, if you ever run into the real germ, your body can respond quickly and prevent you from getting very sick.

There are different types of vaccines:

• Live, attenuated – use a weakened virus (Example: MMR and chickenpox vaccines)
• Inactivated – use a virus that's killed (Example: flu vaccine)
• Toxoid – use a weakened toxin made by bacteria (Example: tetanus vaccine)
• Subunit – use only parts of the virus or bacteria (Example: hepatitis B vaccine)
• Conjugate – join a germ's antigen to a sugar molecule (Example: Hib and pneumococcal vaccines)
• mRNA – help your body make a protein to fight a virus (Example: COVID-19 vaccine)

Are Vaccines Effective?

Yes, vaccines are one of the most effective tools we have to protect people from serious diseases. They help your immune system recognize and fight off infections.

Two key terms help explain this:

• Efficacy – how well a vaccine works in clinical studies. In these studies, some people get the vaccine, and some do not. Scientists then see how many people get sick in each group. For example, if a vaccine is said to be 85% effective, that means people who got the vaccine were much less likely to get sick compared to those who didn’t get it.

• Effectiveness – how well it works in real-world use. Vaccine effectiveness shows how well the vaccine works when it’s used in real life, outside of studies. Even though scientists test the vaccine on many people—different ages, backgrounds, and health conditions—not everyone is the same. So, when more people in the community start getting the vaccine, scientists keep watching to see how well it works for everyone.

Are Vaccines Safe?

Vaccines are very safe for most people. Before a vaccine is allowed to be given, it goes through many tests to make sure it works and doesn’t cause serious problems. Doctors and scientists check vaccines for side effects and watch carefully for any concerns once people start using them. Most side effects from vaccines are mild, like a sore arm or a low fever, and go away quickly. Serious side effects are very rare.

To learn more about vaccine safety, visit:

Healthychildren.org: “Are Vaccines Safe for Children? The Truth About Risks & Benefits”

Healthychildren.org: “Vaccine Safety: Examine the Evidence”

Healthychildren.org: “Vaccine Ingredients: Frequently Asked Questions”

Why Get a Vaccine?

Vaccines save lives. They protect you from serious diseases – and even if you do get sick after being vaccinated, you are less likely to get very sick or have serious problems.

Vaccines also help stop illnesses from spreading to others, like babies, older adults, and people whose bodies can’t fight off germs as easily. Over the years, vaccines have helped get rid of deadly diseases like smallpox and have made other diseases like tetanus, hepatitis, flu, and pneumonia much less common.

In the past 50 years, vaccines have:

• Saved more than 154 million lives world-wide
• Reduced infant deaths by 40%
• Prevented 4 million child deaths each year
• Expected to save 19 million lives from measles and 14 million lives from hepatitis B by 2030

Common Questions

Can you still get sick after getting a vaccine?

Yes, but it’s much less likely. After you get a vaccine, it takes a few weeks for your body to build up full protection and no vaccine is 100% effective. However, if you do get sick, your symptoms are usually milder and you’re much less likely to end up in the hospital or die.

Does a vaccine protect you for your whole life?

Some do, while others require booster shots. Staying up to date with your vaccine schedule is the best way to keep your protection strong.