Vaccine Types

There are several different types of vaccines. Each type is designed to teach your immune system how to fight off certain kinds of germs—and the serious diseases they cause.

When scientists create vaccines, they consider:

• How your immune system responds to the germ
• Who needs to be vaccinated against the germ
• The best technology or approach to create the vaccine

Based on a number of these factors, scientists decide which type of vaccine they will make. There are several types of vaccines, including:

• Inactivated vaccines
• Live-attenuated vaccines
• Messenger RNA (mRNA) vaccines
• Subunit, recombinant, polysaccharide, and conjugate vaccines
• Toxoid vaccines
• Viral vector vaccines

Inactivated vaccines

Inactivated vaccines use the killed version of the germ that causes a disease.

Inactivated vaccines usually don’t provide immunity (protection) that’s as strong as live vaccines. So you may need several doses over time (booster shots) in order to get ongoing immunity against diseases.

Inactivated vaccines are used to protect against:

• Hepatitis A
• Flu (shot only)
• Polio (shot only)
• Rabies

Live-attenuated vaccines

Live vaccines use a weakened (or attenuated) form of the germ that causes a disease.

Because these vaccines are so similar to the natural infection that they help prevent, they create a strong and long-lasting immune response. Just 1 or 2 doses of most live vaccines can give you a lifetime of protection against a germ and the disease it causes.

But live vaccines also have some limitations. For example:

• Because they contain a small amount of the weakened live virus, some people should talk to their health care provider before receiving them, such as people with weakened immune systems, long-term health problems, or people who’ve had an organ transplant.
• They need to be kept cool, so they don’t travel well. That means they can’t be used in countries with limited access to refrigerators.

Live vaccines are used to protect against:

• Measles, mumps, rubella (MMR combined vaccine)
• Rotavirus
• Smallpox
• Chickenpox
• Yellow fever

Messenger RNA vaccines—also called mRNA vaccines

Researchers have been studying and working with mRNA vaccines for decades and this technology was used to make some of the COVID-19 vaccines. mRNA vaccines make proteins in order to trigger an immune response. mRNA vaccines have several benefits compared to other types of vaccines, including shorter manufacturing times and, because they do not contain a live virus, no risk of causing disease in the person getting vaccinated.

mRNA vaccines are used to protect against:

• COVID-19

Subunit, recombinant, polysaccharide, and conjugate vaccines

Subunit, recombinant, polysaccharide, and conjugate vaccines use specific pieces of the germ—like its protein, sugar, or capsid (a casing around the germ).

Because these vaccines use only specific pieces of the germ, they give a very strong immune response that’s targeted to key parts of the germ. They can also be used on almost everyone who needs them, including people with weakened immune systems and long-term health problems.

One limitation of these vaccines is that you may need booster shots to get ongoing protection against diseases.

These vaccines are used to protect against:

• Hib (Haemophilus influenzae type b) disease
• Hepatitis B
• HPV (Human papillomavirus)
• Whooping cough (part of the DTaP combined vaccine)
• Pneumococcal disease
• Meningococcal disease
• Shingles

Toxoid vaccines

Toxoid vaccines use a toxin (harmful product) made by the germ that causes a disease. They create immunity to the parts of the germ that cause a disease instead of the germ itself. That means the immune response is targeted to the toxin instead of the whole germ.

Like some other types of vaccines, you may need booster shots to get ongoing protection against diseases.

Toxoid vaccines are used to protect against:

• Diphtheria
• Tetanus

Viral vector vaccines

For decades, scientists studied viral vector vaccines. Some vaccines recently used for Ebola outbreaks have used viral vector technology, and a number of studies have focused on viral vector vaccines against other infectious diseases such as Zika, flu, and HIV. Scientists used this technology to make COVID-19 vaccines as well.

Viral vector vaccines use a modified version of a different virus as a vector to deliver protection. Several different viruses have been used as vectors, including influenza, vesicular stomatitis virus (VSV), measles virus, and adenovirus, which causes the common cold. Adenovirus is one of the viral vectors used in some COVID-19 vaccines being studied in clinical trials. Viral vector vaccines are used to protect against:

• COVID-19