Vaccination

Question 1

What are vaccines? (1)

Answer 1

Vaccination is the induction of protective immunity to antigens in a vaccine

Question 2

Why are vaccines important? (3)

Answer 2

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

Question 3

Principles of vaccination (5)

Answer 3

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

Question 4

Role of antibodies in vaccination (2)

Answer 4

Most vaccines in clinical use stimulate antibody production

Antibodies provide protection against many pathogens

Question 5

Which antibody is used for blood borne pathogens (1)

Answer 5

IgG is important for humoral immunity against blood borne pathogens

Question 6

Which antibody is used for mucosal pathogens (1)

Answer 6

IgA is important for humoral immunity against mucosal pathogens

Question 7

What are Cytotoxic T lymphocytes (CTL) important for (1)

Answer 7

Cytotoxic T lymphocytes (CTL) are important for intracellular pathogens (viruses)

Question 8

Features of effective vaccines (6)

Answer 8

Safe
Protective
Gives sustained protection - protection against illness must last for several years
Induces neutralising antibody
Induces protective T cells
Practical consideration

Question 9

What are the practical considerations of vaccines (4)

Answer 9

Low cost per dose
Biological stability
Ease of administration
Few side-effects

Question 10

What are the different types of vaccines (5)

Answer 10

Live attenuated vaccines

Inactivated (dead) vaccines

Subunit vaccines

mRNA vaccines (COVID-19

Chimeric vaccines (COVID-19

Question 11

What are live attenuated vaccines? (3)

Answer 11

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

Question 12

What is the oral polio vaccine (2)

Answer 12

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)

Question 13

How was the oral polio vaccine generated? (2)

Answer 13

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

Question 14

What are inactivated vaccines? (3)

Answer 14

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

Question 15

What is Salk inactivated polio vaccine (3)

Answer 15

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

Question 16

How is Salk inactivated polio vaccine generated (2)

Answer 16

Vaccine is grown in cell culture, but chemically inactivated with formaldehyde

Question 17

What are subunit vaccines (3)

Answer 17

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

Question 18

What is Human papilloma virus (HPV) vaccine? (3)

Answer 18

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

Question 19

What is SARS-Cov-2? (2)

Answer 19

SARS-CoV-2 Spike (S) protein binds to ACE-2 on target cell membranes

Question 20

How can antibodies confer protection against SARS-CoV-2? (1)

Answer 20

Antibodies can confer protection by neutralizing SARS-CoV-2 and preventing infection

Question 21

How can vaccines protect against SARS-CoV-2? (1)

Answer 21

Vaccines must (at least in part) produce neutralizing antibodies that block ACE2 interaction

Question 22

What is a P-fizer vaccine (5)

Answer 22

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

Question 23

What is Astra-Zeneca Vaccine? (3)

Answer 23

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

Question 24

In our lifetime, when can we be vaccinated? (4)

Answer 24

Childhood vaccines
Travel vaccines
Vaccines for elderly and vulnerable adults
COVID-19 vaccines

Question 25

Which vaccines cannot be used for subjects with defective immune systems (1)

Answer 25

Live attenuated vaccines
Oral Polio vaccines

Question 26

What is the problem with oral polio vaccine? (2)

Answer 26

Polio vaccine can revert to the
virulent form and can cause vaccine-associated
paralytic polio