Types of Vaccines

Types of Vaccines

En español

Different types of vaccines are available. Click on the different types in the list to learn more and see examples of each.

Combination vaccines

Combination vaccines protect against multiple diseases. The vaccines combine individual vaccines into one shot. This decreases the number of shots that an infant might get in a single visit.

Examples of combination vaccines

Commonly known examples of combination vaccines include MMR, DTaP, Tdap and Td. However, other options your provider may offer include:

  • PROQUAD includes vaccines against measles, mumps, rubella and varicella
  • KINRIX includes vaccines against diphtheria, tetanus, pertussis and polio
  • PEDIARIX includes vaccines against diphtheria, tetanus, pertussis, hepatitis B and polio
  • PENTACEL includes vaccines against diphtheria, tetanus, pertussis, polio and Haemophilus influenzae type b (Hib)
  • TWINRIX includes vaccines against hepatitis A and hepatitis B
  • QUADRACEL includes vaccines against diphtheria, tetanus, pertussis and polio

Inactivated toxoid vaccines

Some bacteria cause sickness by making a poison, called a toxin. Examples include tetanus, pertussis and diphtheria.

Vaccines against these bacteria have to protect people from the toxin. So, they are made by changing the toxin(s) using chemical treatment. The treated toxins are called toxoids.

Examples of inactivated bacterial toxoid vaccines

Pertussis vaccine protects against both the toxin and some parts of the bacteria. The diphtheria and tetanus vaccines only protect against the toxin.

Killed viral vaccines

Killed viral vaccines start with the virus that causes disease. But, it is completely killed with a chemical, called formaldehyde. Because formaldehyde kills the virus, it cannot cause disease.

Examples of killed viral vaccines

Live, “weakened” vaccines

Live, "weakened" viral vaccines

Live, "weakened" viral vaccines are made using a process called "cell-culture adaptation." In this process a virus is grown repeatedly in cells in the laboratory. This makes the virus less able to grow in human cells. Once injected into a person, the vaccine virus reproduces itself fewer times than the “wild type,” or natural virus, would. As a result, the vaccine induces an immune response strong enough to protect against disease. But, the vaccine is not strong enough to cause the disease.

Examples of live, "weakened" viral vaccines

Live, "weakened" bacterial vaccines

Live, “weakened” bacterial vaccines are made using a strain of the bacteria that can generate protective immunity without causing illness. The strain can be developed in two ways:

  • By identifying a naturally occurring strain that has a genetic mutation so it can no longer cause illness. Typhoid vaccine is an example.
  • By genetically engineering the bacteria in a lab. Cholera vaccine is an example.

The altered strain has to be proven to be safe and effective as a vaccine. If it is, it is grown in large quantities in fermentors. The fermentors also contain the nutrients needed for the bacteria to grow.

After being grown, the bacteria are:

  • Purified by filtration or centrifugation
  • Lyophilized (dried)
  • Packaged
Examples of live, “weakened” bacterial vaccines

Nucleic acid vaccines

DNA and RNA are nucleic acids. Living organisms use nucleic acids as blueprints. In people, DNA lives in the nucleus of a cell and directs the activities of the cell. One of the things that happens in the nucleus is that DNA blueprints are used to create messenger RNA, or mRNA. Once mRNA is made, it goes to the cytoplasm of the cell where it is used as a blueprint to make proteins.

There are three types of nucleic acid vaccines, mRNA, DNA and vectored vaccines.

mRNA vaccines

In mRNA vaccines, the mRNA is the blueprint for an important part of the virus that the vaccine is meant to protect against. Upon injection, the vaccinated person’s cells read the blueprint and make the viral protein. The vaccinated person’s immune system recognizes the protein as “foreign” and makes an immune response against it. Because the vaccine only contains a single gene from the pathogen, it cannot cause disease. In other words, our cells make one viral protein and then our immune system responds to that viral protein.

Examples of mRNA vaccines

DNA vaccines

DNA vaccines use an important gene from the pathogen to follow a similar process to mRNA vaccines. But, since the vaccine delivers DNA, it requires an extra step compared with mRNA vaccines. The DNA is used to make mRNA, and then the same process as in mRNA vaccines occurs.

Examples of DNA vaccines
  • Currently, no DNA vaccines are used in people.

Vectored vaccines

A vector vaccine is like a “Trojan horse” in that it delivers part of a pathogen that will allow a person to become immune without becoming sick. These vaccines have two parts:

  • Vector — The vectors are viruses that can infect people without causing illness. For example, adenoviruses that cannot reproduce can be used as vectors.
  • Antigen — The part of the pathogen to which an immune response is needed. This is delivered in the form of the pathogen’s DNA. For example, to be protected against COVID-19, a person’s immune system must recognize the spike protein.

Similar to how other nucleic acid vaccines work, once the vaccine is delivered, the DNA is used to make mRNA, which is then used as a blueprint to make proteins that the immune system responds against. These vaccines are made in a way so that they cannot cause disease in humans.

Examples of vectored vaccines
  • COVID-19 (J&J/Janssen, no longer available in the U.S.)

Polysaccharide vaccines

Two kinds of polysaccharide vaccines have been made. The first kind is conjugated. The second kind is unconjugated.

To make a conjugated vaccine, the sugar coating (polysaccharide) of the bacteria is attached to a harmless protein. An unconjugated vaccine is not attached to an extra protein. The extra protein was added in situations where the unconjugated version did not produce a strong enough immune response. The harmless protein helps the immune system generate a stronger immune response.

Examples of conjugated polysaccharide vaccines
Examples of unconjugated polysaccharide vaccines

Recombinant vaccines

Recombinant vaccines are made by inserting the gene for a viral surface protein into a circular piece of DNA. This circular piece of DNA is known as a plasmid. Plasmids reproduce inside cells even though they are not part of the cell’s genetic material. 

To make the vaccine, the plasmid with the protein is introduced into cells (e.g., yeast cells), so that the surface protein is produced as the cells reproduce. The viral surface protein is then purified and used in the vaccine.

The HPV vaccine is made in this way. Unlike other vaccines of this kind, the HPV surface protein reassembles itself to look like the HPV virus. But, the HPV surface protein does not contain HPV genetic material, so it cannot reproduce or cause illness.

Examples of recombinant vaccines

 

Reviewed by Paul A. Offit, MD, on Nov. 6, 2025