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Despite these disadvantages, inactivated vaccines do have the advantages of long-term storage stability and ease of transport. Also, there is no risk of causing severe active infections. However, inactivated vaccines are not without their side effects. [link] lists examples of inactivated vaccines.

Subunit vaccines

Whereas live attenuated and inactive vaccines expose an individual to a weakened or dead pathogen, subunit vaccines only expose the patient to the key antigens of a pathogen—not whole cells or viruses. Subunit vaccines can be produced either by chemically degrading a pathogen and isolating its key antigens or by producing the antigens through genetic engineering. Because these vaccines contain only the essential antigens of a pathogen, the risk of side effects is relatively low. [link] lists examples of subunit vaccines.

Toxoid vaccines

Like subunit vaccines, toxoid vaccines do not introduce a whole pathogen to the patient; they contain inactivated bacterial toxins , called toxoids. Toxoid vaccines are used to prevent diseases in which bacterial toxins play an important role in pathogenesis. These vaccines activate humoral immunity that neutralizes the toxins. [link] lists examples of toxoid vaccines.

Conjugate vaccines

A conjugate vaccine is a type of subunit vaccine that consists of a protein conjugated to a capsule polysaccharide. Conjugate vaccines have been developed to enhance the efficacy of subunit vaccines against pathogens that have protective polysaccharide capsules that help them evade phagocytosis , causing invasive infections that can lead to meningitis and other serious conditions. The subunit vaccines against these pathogens introduce T-independent capsular polysaccharide antigens that result in the production of antibodies that can opsonize the capsule and thus combat the infection; however, children under the age of two years do not respond effectively to these vaccines. Children do respond effectively when vaccinated with the conjugate vaccine, in which a protein with T-dependent antigens is conjugated to the capsule polysaccharide. The conjugated protein-polysaccharide antigen stimulates production of antibodies against both the protein and the capsule polysaccharide. [link] lists examples of conjugate vaccines.

Classes of Vaccines
Class Description Advantages Disadvantages Examples
Live attenuated Weakened strain of whole pathogen Cellular and humoral immunity Difficult to store and transport Chickenpox, German measles, measles, mumps, tuberculosis, typhoid fever, yellow fever
Long-lasting immunity Risk of infection in immunocompromised patients
Transmission to contacts Risk of reversion
Inactivated Whole pathogen killed or inactivated with heat, chemicals, or radiation Ease of storage and transport Weaker immunity (humoral only) Cholera, hepatitis A, influenza, plague, rabies
No risk of severe active infection Higher doses and more boosters required
Subunit Immunogenic antigens Lower risk of side effects Limited longevity Anthrax, hepatitis B, influenza, meningitis, papillomavirus, pneumococcal pneumonia, whooping cough
Multiple doses required
No protection against antigenic variation
Toxoid Inactivated bacterial toxin Humoral immunity to neutralize toxin Does not prevent infection Botulism, diphtheria, pertussis, tetanus
Conjugate Capsule polysaccharide conjugated to protein T-dependent response to capsule Costly to produce Meningitis
( Haemophilus influenzae , Streptococcus pneumoniae , Neisseria meningitides )
No protection against antigenic variation
Better response in young children May interfere with other vaccines
Practice MCQ 2

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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