Micro 7 - Vaccines

Question 1

What is the R0?

Answer 1

o R0 = the number of people that one sick person will infect on average in a totally susceptible population i.e. the basic reproductive rate
o If the R0 is reduced to <1, transmission of the disease is halted [measles R0 = 18 = high]
o The higher the R0 number, the more contagious the disease is

Question 2

What is the herd immunity threshold (HIT) and how is it calulated?

Answer 2

% of fully immune people required to stop the spread of disease

1-1/R0

Question 3

• Immune response process to vaccine:

Answer 3

o APC macrophage/DC  detect PAMPs (pathogen associated molecular pattern) + DAMPs (damage associated molecular pattern)  take up antigen via PRR (pattern recognition receptor) APC present antigen to naïve helper T-cell  activated T-cell  activates associated B-cell  plasma cells  antibody production:
 Neutralisation of infectivity
 Antibody-dependent cellular cytotoxicity

Question 4

Advantages and disadvantages of an inactivated vaccine + toxoid vaccine

Answer 4

o	Advantages:
	Stable	
	Constituents clearly defined
	Unable to cause infection				
o	Disadvantages:
	Shorter lasting immunity – need several doses
	Local reactions common
	Adjuvant needed

Question 5

• Vaccination with a live vaccine not recommended if

Answer 5

o Pregnant
o Immunocompromised
o The patient is receiving systemic high dose steroids - immunosuppressed
o The patient has received immunoglobulin in the past 3 months – you have given them the antibodies therefore they might not produce a response

Question 6

Describe

inactivated
live
toxoid
subunit
conjugate
heterotypic
viral vectored
nucleic acid

vaccines

Answer 6

inactivated
o Whole microorganism is destroyed by heat, chemicals, radiation or antibiotics  no risk of causing infection

live
o Live organisms are modified to be less virulent
toxoid

o Inactivated toxin components

subunit
o Protein components of the microorganism or synthetic virus-like particles are used

conjugate
o Poorly immunogenic antigens are paired with a protein that is highly immunogenic (adjuvant)

heterotypic
o Using pathogens that infect other animals but do not cause disease in humans/cause mild disease

viral vectored
o Use of a modified virus (e.g. adenovirus) to deliver genetic code for an antigen

nucleic acid
o Use DNA/RNA from pathogen

Question 7

Which polio vaccine is live and which is inactivated

Answer 7

OPV = live attenuated - Sabin (oral)

IPV = inactivated - Salk (injection)

Question 8

What is the job of adjuvants?

Examples of adjuvants?

Answer 8

o Added to enhance the body’s immune response to a vaccine
o Help keep antigens near the site of injection – easily accessed by the immune system cells

o	Al (OH)3 – aluminium hydroxide
o	AlPO4 – aluminium phosphate 

o Mild reaction near the injection site

Question 9

Common components of vaccines

Answer 9

Active components
Adjuvants 
Antibiotics
Stabilisers
Preservatives
Trace components

Question 10

Prerequisites for Successful Disease Eradication (i.e. Smallpox)

Answer 10

• No animal reservoir
• No latent reservoir of infection and no integration of pathogen genetic material into the host genome

• Antigenically stable pathogen with only one/few strains

• Vaccine must induce a lasting immune response
• High coverage required for very contagious pathogens (e.g. measles)

Question 11

COVID Vaccines
Side effects
• Adenoviral vectored vaccines
• Mrna vaccines

Answer 11

• Adenoviral vectored vaccines – risk of
o VITT vaccine induced thrombotic thrombocytopenia
 Comes on 4-42 days post vaccination
 Antibody mediated (platelet factor four antibodies)
 Treat with immunoglobulin
 In severe cases, treat with plasma exchange
 Most common presentation is a clot in the brain

o Capillary leak syndrome

•	Mrna vaccines – Pfizer/Moderna
o	Lymphadenopathy
o	Myocarditis
	Rare
	Predominantly affects males
	Onset 2-3 days after second dose
o	Pericarditis