Vaccines Flashcards
goals of vaccination
- to generate pathogen-specific memory T and B lymphocytes
- to enhance mucosal immunity
the vaccinated individual possesses the ability to ?
mount a rapid secondary immune response that results in the accelerated elimination of the pathogen and protection from clinical disease
results of vaccination
- increased numbers of antigen-specific T and B lymphocytes
- immune cells more sensitive to activation by antigen
- higher affinity neutralizing antibodies, isotype switching, and mucosal production of antibody
requirements for effective vaccines
- safe with few side effects
- protective
- sustained protection (several years)
- induces NEUTRALIZING antibody of the appropriate isotype
- induces protective cytotoxic T cells (if required)
- low cost, stable, ease of administration
live vaccines (attenuated or heterologous) - description
live pathogen with lesser virulence
live, heterologous vaccines
*closely related but of lesser virulence
*presence of cross-reactive antigen
ex = smallpox
live, attenuated vaccines
selected to be less virulent
ex = yellow fever
methods of attenuation for vaccines
- passage of virus in non-human host cells
- mutation or deletion of viral or bacterial virulence gene resulting in infectious but avirulent strain
- use of infectious agent that does not produce clinical disease in humans
advantages of live vaccines
*strong humoral AND cellular response
*long-lived immunity (single dose required)
*potential for development of herd immunity
herd immunity
diminished risk of spread of pathogen to individuals that have not been vaccinated (usually > 80% vaccination in the general population)
disadvantages of live vaccines
*danger of reversion to virulence (contraindicated in immunocompromised and pregnant patients)
*transfer to less responsive individuals
*may not be stable under all storage conditions
*may be expensive to distribute
examples of live vaccines
smallpox
MMR
Sabin (polio)
intranasal influenza
killed (inactivated) vaccines - description
inactivated pathogen that retains antigen structure
examples of killed (inactivated) vaccines
injected influenza
salk (polio)
advantages of killed vaccines
safe (no possibility of reversion to virulent form)
stable
disadvantages of killed vaccines
generally humoral response ONLY
may be short-lived (booster shot required)
subunit (acellular) vaccines - description
antigen only (e.g. surface protein or polysaccaride)
*can be toxoid or conjugate
toxoid subunit vaccines
denatured toxin with intact receptor binding site
(ex = tetanus and diptheria)
conjugate subunit vaccine
bacterial polysaccharide chemically coupled to protein
(ex = haemophilus influenza)
advantages of subunit (acellular) vaccines
safe (not virulent)
stable
lower chance of adverse reactions
disadvantages of subunit (acellular) vaccines
generally humoral response ONLY (weaker)
may be short-lived (booster shots required)
expensive to prepare
generally require ADJUVANT for maximal response
problem with CONJUGATE acellular polysaccharide vaccines
*problem = children < 2 yo do not respond well due to limited T-cell independent B cell function
*solution = conjugate vaccines to those that use a protein carrier to elicit antigen-specific T cells
examples of CONJUGATE acellular polysaccharide vaccines
*Haemophilus influenza
*Streptococcus pneumonia
*Neisseria meningitidis
linked recognition by T and B cells in conjugate vaccines
1) bacterial polysaccharide covalently linked to a toxoid protein
2) antigen-specific B cell reacts with polysaccharide and presents the toxoid protein on HLA class II
3) toxoid-specific T cells recognize the toxoid
nucleic acid (mRNA) vaccines
examples = COVID-19 vaccines (pfizer and moderna)
methods for targeting vaccines
1) what type of immune response is required?
2) what route of administration should be used?
adjuvants - primary role
enhance immune responses by promoting maturation and activation of dendritic cells
types of adjuvants used
*aluminum salts
*liposome-type adjuvants
*flagellin/F1/V (for yersinia pestis)
*cytokines and TLR agonists
