Vaccines 2 Flashcards
What are the five key functions vaccines aim to achieve?
-Induce immunologic memory
-Prevent infection (rarely, e.g., HPV VLP)
-Prevent disease (e.g., polio)
-Reduce transmission (via secretory IgA)
-Enable herd immunity (~80-95% coverage)
Why do most vaccines prevent disease but not infection?
They block systemic spread (e.g., polio to CNS) but not local replication (e.g., gut shedding).
How do vaccines reduce transmission?
Secretory IgA (mucosal) and IgG neutralize virus in secretions (e.g., nasal, intestinal).
What immune responses are critical for? (give examples):
-Polio: IgA (gut) + IgG (systemic) to block CNS invasion.
-HIV: CTLs + broadly neutralizing antibodies (unachieved).
Compare vaccine types:
- Live/attenuated (Sabin polio/MMR): Strong immunity but reversion risk.
-Subunit (HPV L protein VDL): Safe but needs adjuvants.
-DNA/RNA (COVID-19): Rapid design and no cold chain
What are VLP vaccines? Give an example.
Virus-like particles (non-infectious capsids); e.g., HPV L1 protein produced in yeast.
How do DNA vaccines work?
Plasmid DNA encodes antigens → host cells express them, inducing CTLs + antibodies.
Name two viral vectors and their advantages:
-Poxviruses (e.g., MVA): Large genome for multiple genes.
-Adenoviruses (e.g., ChAdOx): Strong T-cell responses.
What are advantages of adenovirus vectors (e.g., AstraZeneca)?
Cold-chain stability, strong T-cell responses, no adjuvant needed.
Why do replication-incompetent vectors avoid pre-existing immunity issues?
Use rare serotypes (e.g., ChAdOx) or animal-derived adenoviruses (e.g., gorilla Ad).
Why is there no HIV vaccine?
Rapid mutation, immune evasion, integrated provirus, lack of correlates of protection.
What limits DNA vaccine efficacy in humans?
Low immunogenicity; solutions: electroporation, cytokine-encoding plasmids (e.g., IL-12).
How do adjuvants (e.g., alum, ISCOMs) enhance vaccines?
Alum prolongs antigen release; ISCOMs promote CTL responses via cytosolic delivery.
