Vaccines have been used to prevent the spread of infections for hundreds of years. Since the first vaccine in 1796 to prevent smallpox, technology has come a long way.1 There are now six different types of vaccines to prevent more than 20 different diseases.2
Learn more about...
How Do Vaccines Work?
Vaccines help to strengthen your body’s natural defenses against disease-causing germs like bacteria and viruses. They contain weakened or inactive parts of germs called antigens. These antigens are harmless and can’t make you sick, but they can still stimulate your immune system.3
Your immune system scans your body, looking for foreign invaders. When you get a vaccine, specialized cells called white blood cells (WBCs) learn how to recognize the antigens present in the vaccine. They do this by making proteins called antibodies that bind to an antigen and mark it for destruction.4 This is known as an immune response. In this way, vaccines teach your immune system how to recognize and destroy a disease-causing germ without getting the infection.3
After getting a vaccine, your immune system will remember the antigen on the germ so it can quickly recognize and destroy it before it makes you sick.3
Learn more about how vaccines work.
Live-Attenuated Vaccines
Live-attenuated vaccines — also known as live vaccines — use a weakened (attenuated) version of a germ to teach your body to recognize and destroy it.5
The first vaccine more than 200 years ago was a live-attenuated vaccine for smallpox. It was discovered that people who were infected with a similar but less severe disease from cows — called cowpox — were also immune to smallpox. When people were intentionally infected with cowpox to prevent smallpox, the first immunization was born.1
Today’s live-attenuated vaccines are made in a laboratory instead of a barn. One way scientists do this is to grow a virus in chicken cells over many generations. With each generation, the virus becomes better at growing in chicken cells and loses its ability to grow in human cells. When this live virus is given to a human as a vaccine, it won’t be able to grow and cause disease, but it can still cause an immune response.6
Live vaccines usually produce a strong and long-lasting immune response because they closely resemble the natural process of infection. Just one or two doses of a live vaccine can provide long-term protection against many diseases. However, live vaccines aren’t appropriate for everyone because they can cause dangerous infections in people with weakened immune systems.5
Live vaccines also have specific storage requirements and must be kept very cold. This can make it difficult to give these vaccines to people in countries that have limited access to refrigerators.5
Live vaccines can be used to prevent the following diseases:5
- Measles, mumps, and rubella (in a combined vaccine called the MMR vaccine)
- Influenza (known as the live-attenuated influenza vaccine or LAIV)
- Rotavirus
- Smallpox and monkeypox
- Chickenpox
- Yellow fever
- Typhoid
- Japanese encephalitis
Live-attenuated vaccines are given in different ways. Some are injected under your skin or into your muscle. Others are pills or drops that are given by mouth or administered as a nasal spray.7
Inactivated Vaccines
Inactivated vaccines use a killed version of the entire pathogen — also known as whole-cell inactivated vaccines — or parts of the pathogen to produce an immune response. They work by exposing your immune system to the antigens on the germ without it causing an infection.5
Inactivated vaccines are made by growing the germs in a laboratory. Scientists use heat or chemicals to kill the germs and inactivate them. When the inactivated virus is given as a vaccine, the immune system can generate a response without causing infection.6
You usually need more than one dose of an inactivated vaccine to help your immune system build a strong defense against the germ. Inactivated vaccines don’t mimic a natural infection the same way a live-attenuated vaccine can, so multiple exposures to the antigens in an inactivated vaccine can help your immune system learn to defend against the germ in an inactivated vaccine.5
Inactivated vaccines can protect you from diseases such as:5
- Hepatitis A
- Influenza (the flu)
- Polio
- Rabies
Inactivated vaccines are given by injection into the muscle of your thigh or arm.7
Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines
Subunit, recombinant, polysaccharide, and conjugate vaccines are different types of inactivated vaccines that use a small part of the germ to produce an immune response instead of the whole germ.8
These vaccines often use proteins and sugars found on the outer coating of a bacteria or virus. Using only a small part of the germ instead of the entire germ can help reduce the side effects of the vaccine while still giving you protection.8
Subunit and Recombinant Vaccines
Subunit vaccines use proteins isolated from the surface of the germ as an antigen.9 A subunit vaccine is considered a recombinant vaccine if the protein is made in a laboratory by a different organism, such as yeast cells.10 For example, a vaccine for the hepatitis B virus is made by teaching yeast cells how to make the hepatitis B surface protein. This protein is isolated from the yeast and used in a vaccine that gives protection from hepatitis B infection.11
Because subunit vaccines use only a small portion of the germ, the immune system can have difficulty building strong protection. Aluminum salts can be used as an immune booster — called an adjuvant — to increase the efficacy of subunit vaccines.5,12 For example, the recombinant vaccine for meningococcal disease is made from several surface proteins found on the outside of the bacteria, along with an aluminum salt as an adjuvant.13 Other subunit and recombinant vaccines can protect against diseases such as:5,9
- Pertussis (whooping cough)
- COVID-19
- Human papillomavirus (HPV)
These vaccines are given as an injection into the muscles of the arm or leg.7
Polysaccharide and Conjugate Vaccines
Polysaccharide vaccines use sugars (polysaccharides) found in the outer coating of the germ as an antigen. Instead of adjuvants, polysaccharides can be attached (or conjugated) to a protein to help strengthen the immune response and boost efficacy. These are known as conjugate vaccines.5
A conjugate vaccine is also available for meningococcal disease. In this type of vaccine, sugars, not proteins, from the outside of the bacteria are attached to a protein known to create a strong immune response.13
Other polysaccharide and conjugate vaccines are available to prevent the following diseases:5
- Haemophilus influenzae type b (Hib)
- Pneumococcal disease14
Toxoid Vaccines
Some bacteria cause disease using a harmful product known as a toxin. Vaccines used against these bacteria can use a weakened version of the toxin — known as a toxoid — to produce an immune response without causing the disease.5
Unlike other inactivated vaccines, toxoid vaccines don’t make you immune to the infection itself. Instead, these vaccines make you immune to the effects of the toxin that causes disease.15
Toxoid vaccines can be used to prevent diseases such as:5
- Diphtheria
- Tetanus
Toxoids are known to produce a strong immune reaction. In fact, tetanus and diphtheria toxoids are often used in conjugate vaccines to strengthen the immune response.13 However, multiple doses may still be necessary to make sure your immune response is long-lasting.5
Toxoid vaccines are given as an injection into the muscle.7
Messenger RNA (mRNA) Vaccines
Messenger RNA (mRNA) vaccines are a new type of vaccine. Unlike other types of vaccines, the active ingredient in mRNA vaccines is not an antigen. Instead of injecting an antigen directly, this type of vaccine uses genetic information called mRNA to teach your cells how to make the antigen. Your cells then present this protein to your immune system to build protection.16
In the US, two mRNA vaccines have been approved to prevent COVID-19 — COMIRNATY, made by Pfizer-BioNTech, and Spikevax, made by Moderna.17 Future vaccines using mRNA technology are currently being investigated to protect against diseases like Zika, influenza, Ebola, rabies, and even cancer.18
These vaccines are injected into the muscle.7
Viral Vector Vaccines
Similar to mRNA vaccines, viral vector vaccines teach your cells how to make a viral protein that acts as an antigen to produce an immune response. However, viral vector vaccines use a harmless version of a different type of virus — known as a viral vector — to deliver information to your cells.17
Johnson & Johnson’s Janssen (J&J/Janssen) COVID-19 vaccine was the only viral vector vaccine that was FDA-approved in the US, but it is no longer available.17 However, this type of vaccine is being studied for other diseases like Ebola, influenza, human immunodeficiency virus (HIV), and Zika.5
The Future of Vaccines
In the future, you might expect to see new types of vaccines, new ways of delivering vaccines, and vaccines to fight against different types of diseases. New vaccines are currently being developed for diseases, including:2
- HIV
- Improved flu vaccines
- Gonorrhea
- Malaria
- Tuberculosis
- Respiratory syncytial virus (RSV)
- Diarrhea caused by E. coli, Shigella, or Norovirus
