Classification of Vaccines

There are two basic types of vaccines: live attenuated and inactivated. Additional types, such as polysaccharide and recombinant, are described in the Pink Book.

Live Attenuated Vaccines

Live attenuated vaccines are produced by modifying disease-producing virus or bacterium in a laboratory. The resulting vaccine organism retains the ability to replicate (grow) and produce immunity, but usually does not cause illness.

  • A relatively small dose of virus or bacteria is administered, which replicates in the body and stimulates an immune response
  • The immune response to a live attenuated vaccine is virtually identical to that produced by a natural infection

Live attenuated vaccines are fragile and can be damaged or destroyed by heat and light, so they must be handled and stored carefully. They can also be rendered ineffective by circulating antibodies that interfere with replication of the organism in the body.

  • Live attenuated vaccines may cause severe reactions in people with immunodeficiency as a result of uncontrolled replication

Examples of live attenuated vaccines currently available include measles, mumps, and rubella vaccine (MMR), varicella (chickenpox) vaccine and zoster (which contains the same virus as varicella vaccine but in much higher amount), yellow fever, rotavirus, and influenza (intranasal). Oral polio vaccine is a live viral vaccine but is no longer available in the United States.

Inactivated Vaccines

Inactivated vaccines are produced by growing the disease-producing virus or bacterium in a culture media, then inactivating it with heat and/or chemicals.

  • They can be whole cell or fractional
  • Since inactivated vaccines are not alive and cannot replicate, they cannot cause disease, even in an immunodeficient person

Inactivated vaccines always require multiple doses. In general, the first dose does not actually produce protective immunity, but, rather, it "primes" the immune system. A protective immune response develops after the second or third dose.

In contrast to live vaccines, in which the immune response closely resembles natural infection, the immune response to an inactivated vaccine is mostly humoral with little or no cellular immunity resulting. Antibody titers against inactivated antigens diminish with time. As a result, some inactivated vaccines may require periodic supplemental doses to increase, or "boost," antibody titers.

Examples of currently available whole-cell inactivated vaccines are limited to inactivated whole viral vaccines (polio, hepatitis A, and rabies). Inactivated whole virus influenza vaccine and whole inactivated bacterial vaccines (pertussis, typhoid, cholera, and plague) are no longer available in the United States.


What is the difference between live and inactivated vaccines?

Live attenuated vaccines are produced from live organisms (viruses or bacteria) that are weakened by chemical or physical processes.They must replicate in the body in order to produce an immune response.

Live vaccines can cause serious or fatal reactions in immunosuppressed people due to the danger of uncontrolled replication of the vaccine virus. People with congenital immunodeficiency, leukemia, lymphoma, or generalized malignancy should not receive live vaccines for this reason.

Inactivated vaccines are produced from organisms that have been killed by physical or chemical processes, and they can be whole cell or fractional. Inactivated vaccines are not alive and cannot replicate.


Characteristics of Live Attenuated and Inactivated Vaccines

Live Attenuated Vaccines

  • Should NOT be given to immunosuppressed people
  • Usually effective with one dose
  • Produce an immune response similar to natural infection
  • Must replicate in the vaccinated person in order to be effective

Inactivated Vaccines

  • Generally require multiple doses
  • Periodic booster doses may be required
  • Made from viruses and bacteria that have been killed
  • Cannot cause disease

Complete the knowledge check below. Note: this is unscored so you will see a group quiz score of 0/0.