Types of Vaccines
About Vaccines

Vaccines work by teaching your immune system to recognize and remember bacteria or viruses. When you get a vaccine, your body makes a memory of the ingredients (also known as antigens). If in the future you are exposed to the actual disease, your immune system can then fight and kill the bacteria or viruses much more quickly. Vaccines are made by manipulating germs or parts of germs. Scientists decide which vaccine type will be the best based on the disease-causing agent and the natural behavior/course of the disease.

The main types of vaccines are:

  • Live, attenuated vaccines
  • Inactivated vaccines
  • Subunit vaccines
  • Conjugate vaccines
  • Toxoid vaccines

Two additional types of vaccines currently being researched are:

  • DNA vaccines
  • Recombinant vector vaccines
Live, attenuated

The whole germ is attenuated (weakened) so that it cannot cause disease, but can cause an immune response. Since these types of vaccines are most similar to the actual disease, they are more effective and often only require one or two doses for lifetime immunity. There is a remote chance that the weakened germ can revert back to its full strength and cause disease. Live attenuated vaccines should not be given to individuals with weakened or damaged immune systems. To maintain potency, live attenuated vaccines require refrigeration and protection from light.

Examples include Measles/Mumps/Rubella (MMR) and Influenza Vaccine Live, Intranasal (FluMist®).

Inactivated

The whole germ is killed using heat or chemicals. The immune system response is not as strong as with live attenuated vaccines, therefore several doses and boosters may be required to achieve immunity. An inactivated vaccine cannot cause disease and is generally safe for those with weakened or damaged immune systems.

Examples include influenza inactivated vaccine (injectable).

Subunit

Only the portions of the germ that cause an immune response are used to create subunit vaccines. These portions of the germ are called antigens. Subunit vaccines can contain from 1 to 20 antigens. Since only the specific, necessary parts of the germ are used for this type of vaccine, the adverse events risk is lower.

Examples include the Hepatitis B vaccine.

Scientists can use the following methods to identify and then obtain the antigens:

  • grow the germ and break it apart to harvest the necessary antigens.
  • create antigen molecules using DNA technology.
Conjugate

Similar to subunit vaccines, conjugate vaccines use only portions of the germ. Many bacteria molecules are coated by a sugar called polysaccharide. This coating hides or disguises the germ (antigens) so that the immature immune systems of infants are not able to recognize it. Therefore, scientists attach the polysaccharide to a stronger protein. When the immune system responds to the protein, it also responds to the polysaccharide.

Examples include Haemophilus Influenza Conjugate Vaccine (Hib) and Pneumoccocal Conjugate Vaccine (Prevnar®).

Toxoid

The toxins secreted by bacteria are inactivated to make toxoid vaccines. This technique is reserved for diseases in which the secreted toxins are the main cause of the illness. Scientists inactivate the toxin by using a diluted chemical solution called formalin. The resulting inactivated toxin, which is called a toxoid, is harmless.

Examples include tetanus and diphtheria vaccines.

DNA vaccines

Scientists hope to extract a portion of the germ's DNA and make copies of it to create a DNA vaccine. This type of vaccine would hopefully produce better protection like a live virus vaccine, but with even less likelihood of producing disease. It would not contain the actual disease causing part of the germ and therefore could not cause the disease. There are currently studies of DNA vaccines for herpes and influenza.

Recombinant vector vaccines

These vaccines are similar to DNA vaccines except the weakened or attenuated germ is used to carry DNA to the cells to stimulate immunity. Similar to live, attenuated vaccines, recombinant vector vaccines are similar to the actual disease. Currently, scientists are working on HIV, rabies, and measles vaccines using this technology.

References