FunMed Week 8: Vaccination

Question 1

1. Briefly explain how a live attenuated vaccine works and give TWO examples of a live attenuated vaccine. (2 marks)

Answer 1

A live attenuated vaccine uses a weakened form of a pathogen (1/2 mark)
that can trigger a mild infection and subsequent immunity to the pathogen without causing the illness (1/2 mark)

Examples include MMR, nasal flu vaccination, rotavirus vaccine, shingles vaccine (1/2 mark each)

Question 2

1. What is COVAX? (1 mark)

Answer 2

COVID-19 Vaccines Global Access, abbreviated as COVAX, is a worldwide initiative aimed at equitable access to COVID-19 vaccines

Question 3

1. Briefly explain the different roles of IgG and IgM antibody in response to infection. Explain the process of immunological memory (3 marks)

Answer 3

Immunoglobulin M (IgM) – IgM antibodies are produced as a body’s first response to a new infection or to a new “non-self” antigen, providing short-term protection.(1/2 mark) They increase for several weeks and then decline as IgG production begins (1/2 mark).

Immunoglobulin G (IgG) –Specific IgG antibodies are produced during an initial infection or other antigen exposure, levels rise in the first few week then decreasing and stabilizing, but never disappearing (1/2 mark). IgG antibodies form the basis of long-term protection against microorganisms. (1/2 mark)

Low levels of IgG retained following previous exposure via infection or vaccination are the basis of the response to re-exposure allowing a faster immune response and the prevention or amelioration of infection. (1 mark)

Question 4

1. Give an example of a viral vector vaccine against COVID 19 (1 mark). Describe the mechanism of action (2 marks)

Answer 4

AstraZeneca/Oxford COVID vaccine is a viral vector vaccine. (1 mark)

Genetic material encoding the spike protein from the COVID-19 virus (1/2 mark) is placed in a modified version of an adenovirus vector (1/2 marks). The vector delivers the genetic material from the COVID-19 virus that gives cells instructions to make copies of the S protein (1/2 mark). Once the cells display the S proteins on their surfaces, the immune system responds by creating antibodies which will trigger an accelerated immune response if the virus is encountered (1/2 mark).

Question 5

1. Define vaccine hesitancy (1 mark)

Answer 5

Delay in acceptance or refusal of safe vaccines despite availability of vaccine services. (1 mark)

Question 6

explain how inactivated vaccines work [2]

do you need boosters? [1]

give two examples [2]

Answer 6

1. Not alive. Cannot replicate
2. Do not cause disease – even in immunodeficient groups
3. Less effective than live-attenuated: require multiple doses
   
   1. First dose: primes the immune system
   2. Protective immunity after 2^nd or 3^rd dose
4. The immune response to an inactivated vaccine is mostly antibody production (unlike closely resembled immune response in attenuated vaccines)
   
   1. (why you need boosters because antibody decrease over time)
5. Examples:
   
   1. Rabies vaccine
   2. Japanese encephalitis vaccine

Question 7

explain how subunit vaccines produce immune response

Answer 7

1. Do not contain any whole bacteria or viruses at all – instead antigens from original pathogen
2. Means a more targeted immune response
3. Hep B
4. Subunit vaccines use only part of a target pathogen to provoke a response from the immune system.

Question 8

explain how toxoid vaccines work [1]
give two examples [2]

Answer 8

1. Toxoid vaccines are made using inactivated toxins produced by bacteria or virus
2. These protein-based toxins are inactivated using heat, chemicals, or other methods
3. The vaccine antigens are not actively multiplying and do not spread to unimmunized individuals.
4. Some vaccines are made with inactivated versions of these toxins
   
   1. Immune response is to the toxin not the whole germ
5. They trigger a strong immune response.
6. Examples:
   
   1. Diphtheria
   2. Tetanus

Question 9

explain how conjugate vaccines work

give two examples

Answer 9

1. Produced by chemically attaching a polysaccharide from the surface of bacteria to a protein molecule through a process called conjugation
   
   1. In most conjugate vaccines, the polysaccharide is attached to diphtheria or tetanus toxoid protein
2. Great safety record
3. Attaching the polysaccharide antigen to a protein makes it possible to prevent bacterial infections in populations where a polysaccharide vaccine is not effective or provides only temporary protection.
4. Long lasting protection: protection of infants and toddlers
5. Examples:
   
   1. MenC
   2. PVC (children’s pneumococcal vaccine): Streptococcus pneumoniae

Question 10

describe the overall use of subunit vaccines

Answer 10

1. 1. Do not contain any whole bacteria or viruses at all – instead antigens from original pathogen
   2. Means a more targeted immune response

Question 11

why do we need boosters for vaccines?

Answer 11

1. Vaccination produces an initial surge in the number of immune cells churning out antibodies and other molecules, which then slowly drops.
2. Leaves behind a small pool of long-lasting ‘memory’ B and T cells that patrol the body for future infections by that pathogen
3. Boosters cause:
   
   1. Antibody-making B cells to multiply, elevating the levels of antibodies against the pathogen once more.
   2. Therefore the pool of memory B cells left behind will be larger than before
   3. Leads to a faster, stronger response to subsequent exposures.
   4. Also: cause a process called affinity maturation, in which ‘engaged’ B cells — those that have been triggered by the vaccine — travel to the lymph nodes:
      
      1. Here, they gain mutations, making the antibodies they produce bind to pathogens more strongly, potentially enhancing their potency.
      2. With repeated exposures to the same antigen, a host will produce antibodies of successively greater affinities.

Question 12

what is affinity maturation?

how can you artificially cause this?

Answer 12

1. Also: cause a process called affinity maturation, in which ‘engaged’ B cells — those that have been triggered by the vaccine — travel to the lymph nodes:
   
   1. Here, they gain mutations, making the antibodies they produce bind to pathogens more strongly, potentially enhancing their potency.
   2. With repeated exposures to the same antigen, a host will produce antibodies of successively greater affinities.

Question 13

what are the roles of B cells in adaptive immunity? e.g. when niave B cells encounter an antigen?

Answer 13

1. In the lymphatic system, naive B cells encounter an antigen, which starts the maturation process for the B cell.
2. it quickly divides (clonal expansion) in order to become either a memory B cell or an effector B cell, which is also called a plasma cell. Antibodies can bind to antigens directly
   
   1. The antigen must effectively bind with a naive B cell’s membrane-bound antibody in order to set off differentiation.
3. Memory B cells express the same membrane-bound antibody as the original naive B cell, or the “parent B cell”. Plasma B cells produce the same antibody as the parent B cell, but they aren’t membrane bound. Instead, plasma B cells can secrete antibodies.
4. B cells also express a specialized receptor, called the B cell receptor (BCR). B cell receptors assist with antigen binding, as well as internalization and processing of the antigen.

Question 14

what is is the role of T cells [3] in adaptive immunity?

Answer 14

1. T cells:
   
   1. Cytotoxic T cells: destroy virus infected cells
   2. Suppressor T cells: deactivate T and B cells when needed
   3. Helper T cells: activate antibody and cell mediated immune response

Question 15

what is the role of antigen presenting cell in adaptive immunity?

give 3 examples of APCs

Answer 15

1. Antigen-presenting cell (APC): When a pathogen is detected, these APCs will phagocytose the pathogen and digest it to form many different fragments of the antigen. Antigen fragments will then be transported to the surface of the APC, where they will serve as an indicator to other immune cells
2. Examples:
   
   1. dendritic cells, macrophages, Langerhans cells and B cells.

Question 16

where do you find dendritic cells? [4]

what is the main role?

Answer 16

Dendritic cells: process antigen material; they are present in the skin (Langerhans cells) and the lining of the nose, lungs, stomach, and intestines

The main function of these innate cells is to capture, process, and present antigens to adaptive immune cells and mediate their polarization into effector cells (1). ​

Question 17

how do recombinant vaccines work?
give two examples

Answer 17

1. Bacterial or yeast cells used to manufacture the vaccine
2. A small piece of DNA is taken from the virus or bacterium against which we want to protect and inserted into the manufacturing cells
   
   1. (For example, to make the hepatitis B vaccine, part of the DNA from the hepatitis B virus is inserted into the DNA of yeast cells.
   2. These yeast cells are then able to produce one of the surface proteins from the hepatitis B virus, and this is purified and used as the active ingredient in the vaccine)
3. Examples:
   
   1. HPV vaccine
   2. MenB
   3. Hep B

Question 18

which antigens can be used for recombinant protein vaccines? [2[

Answer 18

Antigens used include:

Surface polysaccharides
Surface proteins

Question 19

give two examples of toxoid vaccine

Answer 19

1. Diphtheria
2. Tetanus

Question 20

what are rna vaccines?

give two e.g.s

Answer 20

RNA vaccines use mRNA (messenger RNA) inside a lipid (fat) membrane.

This fatty cover both protects the mRNA when it first enters the body, and also helps it to get inside cells by fusing with the cell membrane.

Covid-19 vaccines from Moderna and BioNTech instead deliver a genetic molecule called messenger RNA (mRNA) directly to cells. These encode an antigen—namely the spike protein from the outer coating of SARS-CoV-2 that lets the virus grab onto our cells. The human cell’s own machinery then makes the antigen from the mRNA template and the resulting protein provokes an adaptive immune response. Thus, the body learns to identify, target, and destroy that protein, including live virus particles.

The Pfizer BioNTech and the Moderna COVID-19 vaccines are both RNA vaccines.

Question 21

what are virus-like particle vaccines?

give 2 e.g.s

Answer 21

Virus Like Particles

Virus-like particles (VLPs) are molecules that closely resemble viruses, but are non-infectious because they contain no viral genetic material.

As each VLP has multiple copies of an antigen on its surface it is more effective at stimulating an immune response that a single copy. In some cases, the structural proteins of the VLP can act as adjuvants, helping to strengthen the immune response to the primary target antigen.

A handful of VLP-based vaccines are currently used worldwide:

Hepatitis B vaccine

HPV vaccine

Question 22

what is an adjuvant?

Answer 22

Adjuvants are often added to subunit vaccines.

These are substances which help to strengthen and lengthen the immune response to the vaccine. As a result, common local reactions (such as a sore arm) may be more noticeable and frequent with these types of vaccines.