04. Vaccines Flashcards
Vaccine Definition
Any biologically derived substance that elicits a protective immune response when administered to a susceptible host.
Immune System Basics: Pathogen; Antigen; Antibody
Pathogen: An agent that can cause disease (e.g. virus or bacteria)
Antigen: Any foreign substance that can stimulate an immune response
Antibody: Proteins made by the body to fight against foreign invaders (i.e. antigens)
Pathogens contain antigens; when pathogens invade the body, antigens stimulate the immune system. In response to the antigens, the immune system produces antibodies. Antibodies work to neutralize the pathogen.
How do Vaccines Work
Vaccines contain either parts of microbes or whole microbes that have been killed or weakened. Vaccines work by mimicking disease agents (pathogens) and stimulating the immune system to build up antibodies. Our immune system is capable of memory. If the body is later exposed to the pathogen, the immune system “remembers” and is ready to fight off the pathogen
Immunity definition
Achieved through the presence of antibodies to that disease in a person’s system. Antibodies are proteins produced by the body to neutralize or destroy toxins or disease-carrying organisms. Antibodies are disease-specific.
Active Immunity
Results when exposure to a disease organism triggers the immune system to produce antibodies to that disease. Future exposure will result in immune system recognition and production of antibodies. Takes time to develop (weeks) but is long-lasting. Can occur via: Infection and Vaccination.
Passive Immunity
Results from a person being given antibodies to a disease (rather than antibodies being produced via their own immune system.) Immunity is immediate but short-lived. Can occur via: Mother to child via placenta or breastfeeding. & Antibody containing blood products
Characteristics of Ideal Vaccine
- Produces strong humoral & cell-mediated immune response, similar to natural infection, in a single dose
- Protects against clinical disease and reinfection
- Provides protection for several years, preferably a lifetime
- Results in minimal adverse effects.
- Immunity confers protection against multiple strains of organisms.
- Can be administered simply, in a form that is acceptable to target population
- Vaccine preparations don’t require special handling (e.g. cold chain)
- Does not interfere with immune response of other vaccines given simultaneously
- Costs and benefits outweigh cost and risk of natural infection
Types of Vaccines
- Live Attenuated Vaccine
- Utilizes microorganism that has been attenuated, or weakened, so that it cannot cause disease
- Examples – MMR (measles, mumps, rubella) vaccine, varicella (chickenpox) vaccine
- Inactivated Vaccine
- Utilizes whole or part (protein or polysccharide component) of microorganism that is killed; cannot replicate in host
- Examples – Conjugate Vaccine. pertussis (whooping cough) vaccine, IPV (inactivated polio virus) vaccine
Live Attenuated Vaccines: pros and cons
Advantages:
- Generates strong immune response; both humoral and cell mediated
- Often confers life-long immunity with 1 or 2 doses
Disadvantage
- Can’t be given to those with weak immune systems
- Potential to revert to virulent form
- Requires maintenance of cold chain
- Rarely, antibodies induced by one vaccine can inhibit the immune response to another
Inactivated Vaccines: pros and cons
Advantages:
- Cannot revert to a virulent strain
- Require less stringent handling procedures
- Associated with fewer adverse effects
- Safe to give to immunocompromise
Disadvantages:
- Immune response is weaker; only humoral, no cell-mediated
- Several doses required to reach required antibody level
- Immunity wanes with time; requires booster doses
Immunization Schedules
Goal of effective immunization program is to vaccine a high proportion of susceptible persons early in life or before they are potentially exposed to the infectious agent
Keeping Vaccines Safe
Pre-licensure: Vaccine Development starts with basic laboratory and animal studies research.
- Exploratory: Basic laboratory research, scientist identify antigens that might help prevent/treat disease
- Pre-Clinical Stage – Cell/tissue & animal (mice, monkeys) studies to assess safety and ability to to provoke an immune response, suggest safe starting dose and safe administration method
- Investigational New Drug Application (IND): Submitted to US FDA, Institutional Review Board must approve clinical trial protocols
Post-licensure: Continual Monitoring
- • FDA requires vaccine manufacturers to submit samples from each vaccine lot and test results for vaccine safety, potency, & purity
- Vaccine Adverse Event Reporting System (VAERS)
- Vaccine Safety Datalink (VSD)
Eradication
reduction of an infectious disease’s prevalence in the global host population to zero. No risk of infection or disease in the absence of vaccination or other control measures
Vaccine Efficacy (definition, pros and cons)
- % reduction in disease incidence in a vaccinated group compared to an unvaccinated group under optimal conditions
- Vaccine Efficacy = IU-IV/IU X 100
- Best measured by double-blind RCT
- Commonly required prior to FDA licensure (Phase III trials)
- Advantages: control for biases by randomization, prospective active monitoring for disease, careful tracking of vaccination status
- Disadvantages: complexity and expense, lack of generalizability
Vaccine Effectiveness (definition, pros and cons)
- Ability of vaccine to prevent outcomes of interest in real-world setting
- Vaccine Effectiveness = (1-odds of vaccination among cases/among controls) x 100
- Common study design: retrospective case control (rates of vaccination compared among a set of infected cases and appropriate controls)
- Advantages: cheaper, more generalizable
- Disadvantages: biases can affect results
- Differential case ascertainment
- Differences in healthcare utilization
- Differences in susceptibility or exposure
- Crucial that case finding occurs with same degree of rigor among vaccinated and unvaccinated and that equal effort is made to establish vaccination status for both diseased and non-diseased
