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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.
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.
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.
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 |
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