Types of vaccines

Vaccines: Types & Classification

Comprehensive Notes for Nursing Students

Introduction to Vaccines

Vaccines are biological preparations that provide active acquired immunity against specific infectious diseases. They are critical tools in preventive healthcare that have dramatically reduced the incidence of many potentially lethal diseases worldwide.

Key Concept:

Vaccines train the immune system to recognize and combat pathogens by introducing a harmless form of the pathogen or its components, triggering an immune response without causing disease.

Understanding the different types of vaccines, their mechanisms, and appropriate use is essential for nursing practice, especially in community health, pediatric care, and patient education.

Vaccine Classification Overview

Vaccines are classified based on their composition and mechanism of action. The main categories include:

Based on Composition

• Live-attenuated vaccines
• Inactivated (killed) vaccines
• Subunit vaccines
• Toxoid vaccines
• mRNA vaccines
• Viral vector vaccines

Based on Valency

• Monovalent - targets a single strain/serotype
• Bivalent - targets two strains/serotypes
• Trivalent - targets three strains/serotypes
• Tetravalent - targets four strains/serotypes
• Pentavalent - targets five agents/diseases

Vaccine Classification Mind Map

Figure 1: Vaccine Types and Their Mechanisms of Action

Detailed Explanation of Vaccine Types

1. Live-Attenuated Vaccines

Live-attenuated vaccines contain a weakened (attenuated) form of the pathogen that causes a disease. These vaccines closely resemble a natural infection, providing strong and long-lasting immunity, often with just one or two doses.

Important Considerations:

• Not suitable for immunocompromised patients or pregnant women
• Requires careful storage and handling (cold chain)
• May cause mild symptoms resembling the disease
• Possibility of reversion to virulence (rare)

Examples of Live-Attenuated Vaccines:

• Measles, Mumps, and Rubella (MMR)
• Varicella (Chickenpox)
• Rotavirus
• Yellow Fever
• Oral Polio Vaccine (OPV)
• BCG (Tuberculosis)

Mechanism of Action

Figure 2: How Live-Attenuated Vaccines Work

2. Inactivated (Killed) Vaccines

Inactivated vaccines contain pathogens that have been killed through physical or chemical processes. These vaccines cannot cause disease because the pathogen is dead, making them safer for immunocompromised individuals.

Key Characteristics:

• Cannot replicate in the body
• Usually requires multiple doses for primary series
• Often requires adjuvants to enhance immune response
• Typically needs booster doses to maintain immunity
• More stable than live vaccines (may not require constant refrigeration)

Examples of Inactivated Vaccines:

• Inactivated Polio Vaccine (IPV)
• Hepatitis A
• Rabies
• Some Influenza vaccines (flu shot)
• Whole-cell Pertussis (in DTP vaccine)
• Cholera

Clinical Note:

Inactivated vaccines typically induce a predominantly humoral (antibody) immune response and may not trigger strong cellular immunity. This is why multiple doses are often required to build and maintain adequate protection.

3. Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines

Instead of the entire pathogen, these vaccines include only specific parts (subunits) that best stimulate the immune system. They can be created using various approaches:

Type	Description	Examples
Subunit	Contains purified fragments of the pathogen (proteins, polysaccharides)	Hepatitis B, Acellular Pertussis (in DTaP/Tdap)
Recombinant	Uses genetic engineering to produce specific antigens	HPV, Hepatitis B, Shingles (Shingrix)
Polysaccharide	Contains sugar molecules from bacterial capsules	Pneumococcal (PPSV23), Meningococcal, Typhoid Vi
Conjugate	Polysaccharides linked to carrier proteins to enhance immunogenicity	Hib, Pneumococcal (PCV13), Meningococcal conjugate

Clinical Significance:

Conjugate vaccines represent a significant advancement over plain polysaccharide vaccines. By attaching the polysaccharide to a protein carrier, they convert a T-independent immune response to a T-dependent one, improving immunogenicity in young children and producing immune memory.

Advantages:

• Highly specific immune response
• Cannot cause disease (very safe profile)
• Suitable for immunocompromised individuals
• Often easier to produce and store

Limitations:

• May require adjuvants to boost immune response
• Multiple doses typically needed
• May induce shorter duration of immunity
• More expensive to develop and produce

4. Toxoid Vaccines

Toxoid vaccines use inactivated bacterial toxins (toxoids) to immunize against diseases where the primary cause of illness is the toxin produced by the bacteria, rather than the bacteria itself.

Mechanism of Action:

These vaccines work by chemically inactivating the toxin (usually with formaldehyde) to eliminate its harmful effects while maintaining its ability to trigger an immune response. When the immune system encounters the actual toxin later, it recognizes it and neutralizes it before damage occurs.

Key Examples:

• Tetanus toxoid - Found in DT, DTaP, Tdap, and Td vaccines
• Diphtheria toxoid - Found in DT, DTaP, Tdap, and Td vaccines

Clinical Application

Tetanus toxoid vaccination is crucial for wound management. If a patient has a tetanus-prone wound and:

• Has had <3 doses or unknown history: Give TIG + Td/Tdap
• Has had ≥3 doses but last dose >5 years ago (for dirty wounds) or >10 years (for clean wounds): Booster dose needed

TIG = Tetanus Immune Globulin

5. mRNA Vaccines

mRNA vaccines represent a revolutionary approach in vaccine technology. While the platform gained worldwide attention with COVID-19 vaccines, the technology had been under development for decades before its widespread implementation.

Mechanism of Action:

mRNA vaccines deliver genetic instructions for cells to produce a specific protein (usually a viral surface protein). The cells then display this protein, triggering an immune response. The mRNA never enters the cell nucleus or alters DNA.

Key Advantages:

• Rapid development and manufacturing
• No live components - cannot cause infection
• No integration with host DNA
• Strong immune response (both humoral and cellular)
• Can be adapted quickly for new variants

mRNA Vaccine Process

Figure 3: How mRNA Vaccines Generate Immunity

Storage Considerations:

mRNA is inherently unstable, requiring special storage conditions. The first generation of COVID-19 mRNA vaccines needed ultra-cold storage (-70°C for Pfizer initially, -20°C for Moderna). Newer formulations have improved stability, but cold chain management remains crucial.

Current Examples:

• COVID-19 vaccines (Pfizer-BioNTech, Moderna)
• Research ongoing for influenza, CMV, Zika, and cancer vaccines

6. Viral Vector Vaccines

Viral vector vaccines use a modified version of a different virus (the vector) to deliver important genetic material from the target pathogen to cells. The vector virus is altered so it cannot cause disease but can efficiently transport the genetic instructions to produce antigens.

How They Work:

1. A harmless viral vector (often adenovirus) is modified to carry genetic material from the target pathogen
2. The vector enters cells and delivers genetic instructions
3. Cells produce the target antigen (e.g., spike protein for COVID-19)
4. The immune system recognizes the antigen as foreign
5. Antibodies and T-cells develop against the antigen

Examples:

• COVID-19: Oxford/AstraZeneca, Johnson & Johnson (Janssen), Sputnik V
• Ebola: Ervebo
• In development for HIV, Zika, and other diseases

Advantages & Limitations

Advantages:

• Single dose may be sufficient
• Strong cellular immune response
• No adjuvant needed
• More stable than mRNA (standard refrigeration)
• Technology adaptable to multiple diseases

Limitations:

• Pre-existing immunity to vector may reduce effectiveness
• Complex manufacturing process
• Some associated with rare adverse events (e.g., thrombosis with thrombocytopenia)
• Cannot be used repeatedly with same vector

Figure 4: Mechanism of Action of Viral Vector Vaccines

Helpful Mnemonics for Vaccine Classification

LIVE MTR

Remember common live-attenuated vaccines:

• L - Live attenuated influenza (nasal)
• I - Intranasal influenza
• V - Varicella (chickenpox)
• E - Everything yellow fever
• M - Measles
• T - TB (BCG)
• R - Rotavirus, Rubella

KIPER

Remember common inactivated (killed) vaccines:

• K - Killed organisms
• I - Influenza (injectable)
• P - Polio (IPV)
• E - Encephalitis (Japanese)
• R - Rabies

TORCH Vaccines

A guide to remember vaccines related to TORCH infections:

• T - Toxoplasmosis (no vaccine available)
• O - Other infections (Syphilis, HIV, etc. - limited vaccines)
• R - Rubella (MMR vaccine)

• C - Cytomegalovirus (no approved vaccine yet)
• H - Herpes simplex (no approved vaccine yet)

Note: While not all TORCH infections have vaccines, this mnemonic helps remember which maternal infections are vaccine-preventable (primarily Rubella).

Vaccine Types: Comprehensive Comparison

Vaccine Type	Composition	Immune Response	Advantages	Limitations	Dose Requirements
Live-Attenuated	Weakened pathogen	Strong humoral and cellular immunity	Long-lasting, often lifetime immunity	Contraindicated in immunocompromised	Often single or few doses
Inactivated	Killed pathogen	Primarily humoral immunity	Safe for immunocompromised	Requires multiple doses	Multiple doses + boosters
Subunit	Specific pathogen fragments	Focused immune response	Very safe, minimal side effects	Less immunogenic	Multiple doses + boosters
Toxoid	Inactivated bacterial toxins	Antitoxin antibodies	Prevents toxin-mediated diseases	No protection against infection	Multiple doses + boosters
Conjugate	Polysaccharide linked to protein	Enhanced T-cell dependent response	Effective in infants	Complex manufacturing	Multiple doses based on age
mRNA	Genetic instructions for antigen	Strong humoral and cellular immunity	Rapid development, highly specific	Storage challenges	Typically 2 doses
Viral Vector	Harmless virus carrying target genes	Strong cellular immunity	Durable immune response	Pre-existing vector immunity	Usually 1-2 doses

Table 1: Comprehensive comparison of different vaccine types, their properties, and clinical considerations

Key Points Summary

• Vaccines are classified by their composition, preparation method, and mechanism of action
• Live-attenuated vaccines provide strong, long-lasting immunity but have contraindications for certain populations
• Inactivated vaccines are safer but typically require multiple doses and boosters
• Subunit, recombinant, and toxoid vaccines focus on specific components of pathogens

• Conjugate vaccines significantly improved protection for infants against encapsulated bacteria
• mRNA and viral vector vaccines represent newer technologies with unique advantages
• Vaccine selection depends on pathogen characteristics, target population, and practical considerations like storage and cost
• Understanding vaccine types helps nurses provide appropriate patient education and assess contraindications

References

1. Centers for Disease Control and Prevention. (2022). Vaccine Types. https://www.cdc.gov/vaccines/hcp/admin/storage-handling.html
2. U.S. Department of Health & Human Services. (2022). Vaccine Types. https://www.hhs.gov/immunization/basics/types/index.html
3. World Health Organization. (2023). Vaccines and immunization: What is vaccination? https://www.who.int/news-room/questions-and-answers/item/vaccines-and-immunization-what-is-vaccination
4. National Institute of Allergy and Infectious Diseases. (2019). Vaccine Types. https://www.niaid.nih.gov/research/vaccine-types
5. British Society for Immunology. (2023). Types of vaccines for COVID-19. https://www.immunology.org/public-information/vaccine-resources/covid-19/covid-19-vaccine-infographics/types-covid19-vaccines

Nursing Education Notes on Vaccines: Types & Classification

Created in the style of Osmosis medical notes for nursing students