Vaccination Flashcards
What are vaccines? (1)
Vaccination is the induction of protective immunity to antigens in a vaccine
Why are vaccines important? (3)
Immunity to the vaccine antigens provides protective immunity to the corresponding pathogen antigens
Vaccination has enabled the elimination or control of many devastating human diseases
Vaccination against human pathogens saves millions of lives every year
Principles of vaccination (5)
A vaccine comprises one or more antigens that are present in a pathogen
Unlike the pathogen the vaccine does not cause disease
Lymphocytes that recognise the vaccine antigen(s) also recognise the same antigen(s) in the pathogen
Expansion of vaccine specific lymphocytes therefore confers protection to the antigen(s) in the corresponding pathogen
Vaccination enables the immune system to respond more rapidly and to a greater extent when the pathogen is encountered
Role of antibodies in vaccination (2)
Most vaccines in clinical use stimulate antibody production
Antibodies provide protection against many pathogens
Which antibody is used for blood borne pathogens (1)
IgG is important for humoral immunity against blood borne pathogens
Which antibody is used for mucosal pathogens (1)
IgA is important for humoral immunity against mucosal pathogens
What are Cytotoxic T lymphocytes (CTL) important for (1)
Cytotoxic T lymphocytes (CTL) are important for intracellular pathogens (viruses)
Features of effective vaccines (6)
Safe
Protective
Gives sustained protection - protection against illness must last for several years
Induces neutralising antibody
Induces protective T cells
Practical consideration
What are the practical considerations of vaccines (4)
Low cost per dose
Biological stability
Ease of administration
Few side-effects
What are the different types of vaccines (5)
Live attenuated vaccines
Inactivated (dead) vaccines
Subunit vaccines
mRNA vaccines (COVID-19
Chimeric vaccines (COVID-19
What are live attenuated vaccines? (3)
Attenuation reduces the virulence of a pathogen whilst retaining antigens that can promote an immune response
These vaccines are infectious, but they are attenuated such that they cannot cause disease in normal subjects
These vaccines are the most effective in promoting immunity, but cannot be used for subjects with defective immune systems
What is the oral polio vaccine (2)
Oral polio vaccine is a live attenuated vaccine that
contains 3 attenuated strains of the virus
Administered orally and can transiently infect the host, where the vaccine colonises the intestine and stimulates IgA production (mucosal immunity)
How was the oral polio vaccine generated? (2)
Generated by passaging the virus in monkey kidney epithelial cells, resulting in mutations in the polio genome, with the type 3 Sabin strain differing from the wildtype virus in 10 out of 7429 nucleotides
What are inactivated vaccines? (3)
Involves the production of the infectious agent, which is then inactivated (killed) before use.
They cannot replicate and hence pose less risk than live attenuated vaccines and can be used to vaccinate subjects with defective immune systems
However, as they cannot replicate they do not persist as long as a live vaccine in vaccinated subjects and may not induce protective immunity to the same extent
What is Salk inactivated polio vaccine (3)
Contains strains of 3 different polioviruses
Is administered by intramuscular injection and therefore produces less mucosal immunity than the Sabin vaccine.
Cannot revert to a virulent strain
How is Salk inactivated polio vaccine generated (2)
Vaccine is grown in cell culture, but chemically inactivated with formaldehyde
What are subunit vaccines (3)
Subunit vaccines contain parts of the pathogen:
- they can be molecules associated with the pathogen
- they can be inactivated toxins (toxoids) secreted by pathogens
Subunit vaccines may not be as immunogenic as whole pathogen, but are safer to use and to produce
What is Human papilloma virus (HPV) vaccine? (3)
Gardisil is a subunit vaccine that protects against HPV types 6, 11, 16 and 18, which are linked to cervical cancer
The antigens used are the L1 capsid proteins of these HPV types, which produce virus-like particles
Non-infectious, as no nucleic acid, but produce an antibody mediated response
What is SARS-Cov-2? (2)
SARS-CoV-2 Spike (S) protein binds to ACE-2 on target cell membranes
How can antibodies confer protection against SARS-CoV-2? (1)
Antibodies can confer protection by neutralizing SARS-CoV-2 and preventing infection
How can vaccines protect against SARS-CoV-2? (1)
Vaccines must (at least in part) produce neutralizing antibodies that block ACE2 interaction
What is a P-fizer vaccine (5)
mRNA encoding S-protein in lipid nanoparticles
Administered by injection
Fusion of lipid particles carrying mRNA with host
mRNA translated by cellular ribosome to produce spike proteins
Induce an antibody mediated response
What is Astra-Zeneca Vaccine? (3)
ChAdOx1 nCoV-19is chimeric replication-deficient virus
Modified chimpanzee adenovirus that has the sequence for S-protein
ChAdOx1 nCoV-19 infects cells, although it does not replicate it expresses the S-protein
In our lifetime, when can we be vaccinated? (4)
Childhood vaccines
Travel vaccines
Vaccines for elderly and vulnerable adults
COVID-19 vaccines
Which vaccines cannot be used for subjects with defective immune systems (1)
Live attenuated vaccines
Oral Polio vaccines
What is the problem with oral polio vaccine? (2)
Polio vaccine can revert to the
virulent form and can cause vaccine-associated
paralytic polio
