Give a detailed account on the classification of vaccine

Reading File

Finding Sources

Searching PubMed

vaccines AND classification

Searching the Web

WHO vaccine types live attenuated inactivated subunit toxoid conjugate viral vector nucleic acid

Reading File

Finding Sources

Reading Web Page

https://iris.who.int/server/api/core/bitstreams/fae2623c-0fa…

Classification of vaccines

A vaccine is a biological preparation that exposes the immune system to an antigen or to genetic instructions for producing an antigen. It induces active, specific immunity and immunological memory without causing the usual clinical disease.

Vaccines can be classified in several complementary ways:

By nature of the immunizing material
By whether the organism is live or non-living
By technological platform
By route and composition
By number of antigens or diseases covered

The most important practical classification is by the type of antigen/platform.

1. Live attenuated vaccines

These contain live organisms that have been weakened, or attenuated, so that they replicate to a limited extent but normally do not cause disease in immunocompetent recipients.

Mechanism

Because they resemble natural infection, they stimulate:

Humoral immunity, including neutralizing antibodies
Cell-mediated immunity
Often mucosal immunity when administered orally or intranasally
Long-lasting immune memory

Features

Usually highly immunogenic
Often need fewer doses than non-live vaccines
Usually do not require an adjuvant
Must be stored carefully because viability is necessary
May very rarely cause disease in severely immunocompromised persons
Generally avoided in pregnancy and significant immunodeficiency

Examples

Live viral vaccines

BCG is bacterial, not viral, but is commonly remembered with live vaccines
Measles
Mumps
Rubella
MMR and MMRV
Varicella
Live zoster vaccine
Rotavirus vaccine
Oral poliovirus vaccine, OPV
Yellow fever vaccine
Live attenuated influenza vaccine, intranasal
Smallpox vaccine

Live bacterial vaccines

BCG vaccine
Oral typhoid vaccine, Ty21a
Oral live cholera vaccines in certain settings

Goodman and Gilman lists BCG, oral typhoid and oral cholera among live bacterial vaccines, and MMR, varicella, rotavirus, intranasal influenza and yellow fever among live viral vaccines. Goodman & Gilman's The Pharmacological Basis of Therapeutics, vaccine section.

Limitations

Interference by maternal antibodies can reduce response in infants.
Storage and cold-chain failure can reduce potency.
OPV carries a rare risk of vaccine-associated paralytic poliomyelitis and vaccine-derived poliovirus transmission, which is why many countries use IPV in routine programs.
Not routinely given to people with severe cellular immunodeficiency or to pregnant individuals.

2. Inactivated or killed whole-organism vaccines

These contain whole bacteria or viruses that have been killed by heat, chemicals, or radiation. They cannot replicate in the recipient.

Mechanism and features

Primarily stimulate antibody-mediated immunity.
Cannot revert to virulence or cause infection.
Safer for immunocompromised people than live vaccines in most circumstances.
Usually require multiple primary doses and booster doses.
Often require an adjuvant.

Examples

Inactivated viral vaccines

Inactivated poliovirus vaccine, IPV
Hepatitis A vaccine
Rabies vaccine
Most injectable influenza vaccines
Japanese encephalitis vaccine
Tick-borne encephalitis vaccine
Some COVID-19 vaccines, for example whole-virion inactivated products

Inactivated bacterial vaccines

Whole-cell pertussis vaccine
Killed cholera vaccine
Killed typhoid vaccine
Plague vaccine, where used

Advantages

No risk of replication or vaccine-acquired infection
Relatively stable compared with live vaccines
Can be given when live vaccines are contraindicated

Disadvantages

Immune response is generally less durable than after live vaccination.
Multiple doses and boosters are commonly needed.
They usually generate little mucosal immunity.

3. Toxoid vaccines

Some bacteria cause disease mainly through an exotoxin rather than by invasive multiplication alone. A toxoid vaccine contains an inactivated bacterial toxin that retains its antigenicity but has lost toxicity.

Mechanism

The vaccine induces antitoxin antibodies, which neutralize the toxin when the vaccinated person encounters the organism.

Examples

Tetanus toxoid
Diphtheria toxoid

These are used alone or in combination vaccines:

DTaP: diphtheria, tetanus and acellular pertussis
DT
Td
Tdap

Features

Safe and non-replicating
Need primary series plus periodic booster doses because antibody concentrations decline
Protection is chiefly against toxin-mediated disease, not always against colonization or carriage

4. Subunit vaccines

Subunit vaccines contain only selected antigenic components of a pathogen rather than the complete organism. The antigen may be a protein, glycoprotein, purified surface component, or another defined antigenic fragment.

Features

Cannot cause the infection
Usually have fewer adverse effects than whole-cell vaccines
Often require adjuvants and booster doses
Antigen selection is important because only included antigens induce protection

Examples

Acellular pertussis vaccine
Recombinant hepatitis B vaccine
Recombinant zoster vaccine
Human papillomavirus, HPV, vaccine
Some influenza vaccines, including split-virus or purified subunit formulations
Protein-based COVID-19 vaccines

The Harriet Lane Handbook describes subunit, recombinant, polysaccharide and conjugate vaccines as using defined pathogen components such as protein, sugar, or capsid, with boosters sometimes required. The Harriet Lane Handbook, Active Immunization section.

Subtypes of subunit vaccines

A. Protein subunit vaccines

Contain purified pathogen proteins.

Examples:

Acellular pertussis
Recombinant zoster vaccine
Recombinant hepatitis B vaccine

B. Virus-like particle vaccines

These contain self-assembled viral structural proteins that resemble a virus but contain no viral genetic material. They cannot replicate.

Examples:

HPV vaccine
Some hepatitis B vaccine formulations

C. Recombinant vaccines

The antigen is produced using recombinant DNA technology, often in yeast, bacteria, insect cells, or mammalian cells.

Examples:

Hepatitis B vaccine, containing recombinant hepatitis B surface antigen
HPV vaccine
Recombinant zoster vaccine

5. Polysaccharide vaccines

These contain purified capsular polysaccharides from bacteria.

Mechanism

They primarily induce a T-cell-independent B-cell response.

Consequences of T-cell-independent response

Mainly IgM, with limited class switching
Weak immunologic memory
Less effective in children younger than 2 years
Repeated doses may produce hyporesponsiveness for some antigens
Limited effect on nasopharyngeal carriage

Examples

Pneumococcal polysaccharide vaccine, PPSV23
Meningococcal polysaccharide vaccine
Typhoid Vi polysaccharide vaccine

Goodman and Gilman lists meningococcal polysaccharide vaccine, polyvalent pneumococcal vaccine and typhoid Vi polysaccharide vaccine under bacterial polysaccharide vaccines. Goodman & Gilman's The Pharmacological Basis of Therapeutics, vaccine section.

6. Conjugate vaccines

A conjugate vaccine contains a bacterial capsular polysaccharide chemically linked to a carrier protein, such as tetanus toxoid, diphtheria toxoid, or CRM197 diphtheria protein.

Why conjugation is important

Polysaccharide alone causes a poor T-cell-independent response in infants. Linking it to protein converts the response into a T-cell-dependent immune response.

This leads to:

Better response in infants and young children
Immunologic memory
Antibody class switching, especially IgG
Strong booster response
Reduced nasopharyngeal carriage and herd protection

Examples

Hib conjugate vaccine
Pneumococcal conjugate vaccines, such as PCV
Meningococcal conjugate vaccines, such as MenACWY
Typhoid conjugate vaccine

The distinction matters clinically: compared with plain polysaccharide vaccines, conjugate vaccines induce memory and improve protection in young children.

7. Nucleic acid vaccines

These do not supply the antigen itself. Instead, they provide genetic instructions that allow host cells to produce the antigen, which is then recognized by the immune system.

A. mRNA vaccines

These contain messenger RNA, usually packaged in lipid nanoparticles. Host-cell ribosomes translate the mRNA into antigenic protein.

Features

No live pathogen
No integration into human DNA
Capable of inducing antibody and T-cell responses
Rapid platform design after an antigen sequence is known

Examples

Several COVID-19 mRNA vaccines

B. DNA vaccines

These contain plasmid DNA encoding an antigen.

Features

Stable platform, often easier to store than mRNA
May require special delivery systems, such as electroporation
Used widely in veterinary medicine and under continuing development for many human indications

8. Viral-vector vaccines

These use a modified virus as a delivery system for genetic material encoding an antigen of another pathogen.

The vector enters cells, which then produce the target antigen.

Types

Non-replicating viral vectors: vector enters cells but cannot complete replication.
Replicating viral vectors: vector replicates to some degree and may produce stronger immune stimulation.

Examples

Adenoviral-vector COVID-19 vaccines
Ebola vaccine using vesicular stomatitis virus vector
Some experimental malaria, tuberculosis and HIV vaccines

Advantages

Induce both antibody and cellular immune responses
Can be manufactured using established vector platforms

Limitations

Pre-existing immunity to the vector can lower effectiveness.
Subsequent doses using the same vector may be less immunogenic.
Safety and reactogenicity vary by vector platform.

The WHO groups viral-vector and nucleic-acid platforms among newer vaccine technologies, alongside traditional live-attenuated, inactivated, polysaccharide and toxoid vaccines and modern conjugate and protein-based vaccines in its global vaccine market report.

9. Combination vaccines

A combination vaccine protects against more than one disease in one injection or formulation.

Examples

DTaP
DTaP-IPV
DTaP-HepB-IPV
DTaP-IPV-Hib
MMR
MMRV
Hepatitis A and hepatitis B combination vaccine
Pentavalent vaccine: DPT, hepatitis B and Hib
Hexavalent vaccine: DTaP, IPV, Hib and hepatitis B

Advantages

Fewer injections
Better adherence to immunization schedules
Fewer clinic visits
Simplified logistics and record-keeping

A combination vaccine is not necessarily a separate antigen technology. For example, it can combine toxoids, inactivated antigens, protein subunits and conjugate components.

10. Classification by valency

Valency denotes the number of strains, serotypes, or antigenic types included.

Monovalent: one antigenic type
Example: monovalent hepatitis B vaccine.
Bivalent: two types or strains
Example: bivalent oral poliovirus vaccine.
Trivalent: three types or strains
Example: trivalent influenza vaccine.
Quadrivalent: four types or strains
Example: quadrivalent influenza vaccine or quadrivalent meningococcal vaccine.
Multivalent or polyvalent: several antigenic types
Example: PPSV23, which targets multiple pneumococcal serotypes; multivalent HPV vaccines.

Valency should not be confused with the number of diseases prevented by a combination vaccine.

11. Classification by route of administration

Oral vaccines

OPV
Rotavirus vaccine
Oral typhoid vaccine
Some oral cholera vaccines

They can stimulate intestinal mucosal immunity.

Intranasal vaccines

Live attenuated influenza vaccine

Intradermal vaccines

BCG
Some rabies vaccine schedules

Subcutaneous vaccines

MMR
Varicella
Yellow fever

Intramuscular vaccines

DTaP/Tdap
Hepatitis A and B
IPV
HPV
Influenza vaccines
Pneumococcal and meningococcal vaccines
Most COVID-19 vaccines

12. Classification by effect on the immune system

Active immunization

Administration of antigen or genetic antigen instructions to stimulate the recipient's own immune response.

Examples:

All routine vaccines
Toxoids
Live, killed, subunit, conjugate, vector and mRNA vaccines

Features:

Protection develops after days to weeks
Generates memory
Generally long-lasting, though boosters may be necessary

Passive immunization

Administration of preformed antibodies. This is not vaccination in the strict sense.

Examples:

Rabies immunoglobulin
Tetanus immunoglobulin
Hepatitis B immunoglobulin
Antivenom
Maternal antibodies transferred across the placenta
Some monoclonal antibodies, for example preventive antibodies against RSV

Features:

Immediate but temporary protection
No immunological memory

Summary table

Vaccine type	Main material	Typical immune response	Examples	Main limitation
Live attenuated	Weakened live organism	Strong humoral and cellular immunity	BCG, MMR, varicella, OPV, rotavirus	Avoid in severe immunodeficiency and pregnancy
Inactivated	Killed whole organism	Mainly antibody response	IPV, rabies, hepatitis A, injectable influenza	Multiple doses and boosters
Toxoid	Inactivated toxin	Antitoxin antibody	Tetanus, diphtheria	Periodic boosters needed
Protein/subunit	Selected antigenic protein	Mainly antibody, sometimes T-cell response	Hepatitis B, acellular pertussis, zoster	Often needs adjuvant and boosters
Virus-like particle	Noninfectious protein shell	Strong neutralizing antibody response	HPV	Limited to included antigen types
Polysaccharide	Bacterial capsule antigen	T-cell-independent antibody response	PPSV23, typhoid Vi	Weak in children under 2 years, little memory
Conjugate	Polysaccharide linked to protein	T-cell-dependent response with memory	Hib, PCV, MenACWY, typhoid conjugate	More complex and costly production
Viral vector	Vector virus carrying antigen gene	Antibody plus T-cell response	Ebola and some COVID-19 vaccines	Anti-vector immunity may affect response
mRNA/DNA	Genetic instructions for antigen	Antibody and T-cell response	mRNA COVID-19 vaccines	Storage and delivery constraints vary
Combination	More than one antigen/product	Depends on components	DTaP-IPV-Hib, MMR, pentavalent	Compatibility and schedule complexity

Key distinction to remember:

Live vaccines replicate minimally and usually give strong, durable immunity.
Inactivated, toxoid and subunit vaccines cannot replicate and commonly need repeated doses or boosters.
Plain polysaccharide vaccines have poor memory responses in young children.
Conjugate vaccines overcome this limitation by attaching polysaccharide to a protein carrier.

This is a shared conversation. Sign in to Orris to start your own chat.