creation date: 2025-12-19 13:51
tags: PharmacologyIncomplete
Vaccines
Background
Immunity
The benefits of vaccination occurs both at the individual level and at the population level.
At the individual level, a vaccine may passively or actively strengthen the body’s resistance to pathogen. If enough of a population has been immunized, herd immunity allows for nonvaccinated individuals to be protected (eg. children). High immunity rates over prolonged periods may result in eradication of disease (smallpox, 1980 and rinderpest, 2011).
Vaccine Types
Passive Immunization
Involves the injection of preformed antibodies which act against a specific pathogen rapidly. The protection is temporary as antibodies have a half-life of approximately 3 weeks and once the concentration is too low, protection dissipates.
Common indications include acute, post-exposure treatment against a pathogen or in conjunction with an active vaccine.
Examples:
- Viruses: rubella, rabies, hepatitis B
- Toxins: tetanus, botulinum, diphtheria
Active Immunization
Active immunization involves the injection of a variant of a pathogen and allowing the body’s immune system to react to the antigens to produce antibodies.
Onset is slower but immunity usually lasts longer (years to lifetime). It should be noted that natural infection produces immunity through active immunization as well.
A number of different active vaccinations are possible which is described below.
Live-attenuated
Modified functioning virus or bacterium that can replicate in the body but does not cause disease. This generates an infection similar to the natural pathogen which includes specific B-cell formation for long-term memory.
Administration
- Oral or subcutaneous/intramuscular injection in children >12 months
- Not indicated in children <9 months except for rotavirus
- Second dose used for non-responders (not booster)
- Multiple live vaccines can be given simultaneously but if not together, at least 4 weeks apart
- May be administered simulataneously with inactivated vaccines
- May become virulent again rarely - typically contraindicated in immunodeficient individuals and pregnant people
- HIV-positive individuals can be vaccinated if CD4 cell count ≥200 cell/mm3
Examples
- MMR
- Varicella
- Zoster
- Yellow fever
- Rotavirus
- Influenza (intranasal)
- Smallpox
- Adenovirus
- BCG
- Typhoid
Inactivated
Pathogens are inactivated or killed using chemical or heat so that they are unable to replicate are administered. The surface epitopes remain intact and trigger the immune response.
The response triggered is weaker but is considered safer than live vaccines. Vaccines can be whole, made up of proteins subunits (toxoids or antigenic subunits) or polysaccharides subunits (ie. cell wall).
Administration
- Intramuscular injection (deltoid or vastus lateralis)
- First dose does not provide protective immunity and multiple doses are required
- Periodic boosts are necessary to ensure sufficient antibody titers
- May not be consistently immunogenic in infants
Examples
| Type | Whole | Subunit (protein) | Toxoid (protein) | Polysaccharide |
|---|---|---|---|---|
| Vaccines | Polio, Hep A, Rabies, Typhoid, Influenza, Pertussis (cellular), Cholera | Hep B, Influenza, Pertussis (acellular), HPV (6, 11, 16, 18), Anthrax | Diphtheria, Tetanus | Hib, Pneumococcal, Meningococcal, Salmonella typhi |
Viral vector
Unrelated virus is modified and used as a nonpathogenic vector to deliver genetic code that produces the desired antigen.
In nonreplicating vector vaccines, vaccine antigens are produced following administration but new viral particles are not. In replicating vector vaccines, viral particles replicate along with vaccine antigens which propagate further antigen production.
Administration
- Injected intramuscularly but intranasal, intradermal, and oral available
- Preexisting immunity to viral vector may affect effectiveness
Examples
- Ebola virus vaccine
- COVID-19 vaccine (Janssen, Vaxzevria, Sputnik V)
Nucleic acid
mRNA that codes for specific antigen is delivered to cells. In nonreplicating mRNA vaccines, the sequence contains the desired antigen and 3’/5’ UTRs. In self-amplifying mRNA vaccines, the sequence of the antigen is included with viral replication machinery (eg. RNA polymerase) which allows for RNA amplification intracellularly.
The delivery of the vaccine can range from naked mRNA to encapsulated within nanoparticles or polyplex.
Administration
- Injected intramuscularly or intradermally
- Requires multiple doses
- No risk of infection as mRNA is not integrated to DNA nor pathogenic
- Requires strict cold-chain
Examples
- COVID-19
Populations
Pregnancy
| Vaccine | Schedule | Notes |
|---|---|---|
Infants and Children
Routine Adult
Special Considerations
Vaccines
Bacille Calmette Guerin (BCG)
Purpose
Schedule
Preparations and administration
Indications
COVID-19
Purpose
Schedule
Preparations and administration
Indications
Diphtheria, Tetanus, acellular Pertussis (DTaP/Tdap)
Purpose
Schedule
Preparations and administration
Indications
Ebola virus
Haemophilus influenzae type B
Hepatitis A
Hepatitis B
Herpes zoster (Shingles)
Human papillomavirus (HPV)
Influenza
Measles, Mumps, Rubella (MMR)
Pneumococcal
Poliomyelitis (Polio)
Rabies
Respiratory syncytial virus (RSV)
Rotavirus
Smallpox and mpox
Varicella (chickenpox)
References
Tools / Guidelines
National Advisory Committee on Immunization (NACI)
OHIP Vaccination Resources