Vaccination

Question 1

Purpose of vaccination

Answer 1

To induce protective levels of immunity at appropriate site, of relevant nature and of adequate duration
Aim is to protect individuals against infection and clinical disease, and to eradicate disease or otherwise protect whole population
Major causes of mortality and morbidity are now rare due to vaccination

Question 2

Principles of herd immunity

Answer 2

Results in less risk to individuals who have not developed immunity
Chain of infection is disrupted when large numbers of a population are immune
Smaller probability of a susceptible individual coming into contact with an infectious individual
Herd immunity threshold 80-95%

Question 3

Primary and secondary responses following antigen exposure

Answer 3

Primary: 7-20 day latent period, IgM is only response
Secondary: 5-7 day latent period, IgG, IgA and IgE response
T-cell dependent

Question 4

Objective of atteuation

Answer 4

Produce modified organism which mimics natural behaviour of original microbe without disease
Attenuate the virulence components while maintaining the immunogenic components
Viral vaccines e.g. rotavirus, MMR, polio

Question 5

Live attenuated vaccines

Answer 5

Do not need adjuvant, lower dose antigen injected
Ability to replicate within host provides for higher more sustained dose of antigen
Administration by natural portal of infection allowing immune responses at site of natural infection e.g. polio
Ability to infect cells leads to activation of cytotoxic T cell populations, important for intracellular microorganisms

Question 6

Disadvantages of live attenuated vaccines

Answer 6

Insufficient attenuation
Reversion to wild type
Heat lability
Administration to immunodeficient/ at risk patients- e.g. immunodeficient, malignancy or pregnancy

Question 7

Killed vaccines

Answer 7

Used when live attenuated vaccine unavailable or reversion to wild-type is real concern
Need to ensure that live un-attenuated microorganisms are completely removed and that important immunogenic components are not destroyed

Question 8

Advantages and disadvantages of killed vaccines

Answer 8

Satisfactory heat lability, non-infectious relative safety, ease of generation
Generally less immunogenic with immunization usually by multiple administrations with need for adjuvant, mainly humoral immunity (IgG) with little cytotoxic T-cell involvement, administration by parenteral route- not natural port of infection

Question 9

Subunit vaccines

Answer 9

Whole organism contains many antigens, vaccination with isolated immunogenic components may avoid problems such as hypersensitivity, increases potential for totally synthetic products, identification and generation of invariant antigen/ immunogens is the real challengs

Question 10

Subunit vaccine examples

Answer 10

Subcellular e.g. miningococcal
Toxoids e.g. diphtheria/ tetanus
Proteins e.g. Hep B

Question 11

Diphtheria

Answer 11

Gram +ve toxin prevents cells from making new proteins, in children under 5 years had fatality rate of 20%, spread by direct physical contact or breathing the aerosolized secretions of infected individuals
Upper respiratory tract illness with sore throat and low grade fever leading to breathing and swallowing difficulties and obstruction to breathing, abnormal cardiac rhythms leading to heart failure, paralysis of neck, throat or respiratory muscles
Severe cases hospital intensive care units administered diphtheria antitoxin

Question 12

Diphtheria vaccine

Answer 12

Vaccine prepared from the toxin absorbed on aluminium hydroxide or aluminium phosphate to improve antigenicity
High dose vaccine used in children up to 10 years old, low dose used in individuals over 10 years where satisfactory immune response is shown
Single-antigen diphtheria vaccine is not available but given as a combination product containing other vaccines

Question 13

Tetanus

Answer 13

Characterised by muscular rigidity and intermittent spasms, only vaccine preventable disease which is non communicable
Caused by a neurotoxin which grows anaerobically in a contaminated wound, toxin taken up by nerves and blocks inhibitory synapses
Can never be eradicated as the spores are commonly present in the soil

Question 14

Types of tetanus

Answer 14

Local tetanus: muscle spasms in areas contiguous to wound, spasms may continue for several weeks, may precede generalised tetanus
Generalised tetanus: spasms of the jaw and neck muscles, proceeds to involve muscles of the throat, abdomen and extremities, complete recovery may take months

Question 15

Pertussis/ whooping cough

Answer 15

Caused by bacteria spread by droplet infection, ranges from mild disease to death, commonly lasts 2-3 months even when treated with antibiotics, can involve a degree of lung collapse or bronchopneumonia, CNS effects involve altered consciousness or convulsions from lack of oxygen or small bleeding into the brain, potential for permanent brain damage

Question 16

Pertussis subunit vaccine

Answer 16

Prepared from highly purified selected components of pertussis organism, adsorbed onto adjuvants
Acellular vaccines differ, potentially resulting in differences in efficacy and frequency of adverse effects

Question 17

Polio

Answer 17

Acute viral disease, highly infectious, transmission by contact with faeces or pharyngeal secretions
Invasion through GI tract by one of three serotypes, virus replicates in gut and has high affinity for nervous tissue, spread through body via bloodstream or retorgrade axonal transport to CNS
Flu like symptoms to aseptic meningitis and death

Question 18

History of polio vaccines

Answer 18

Until 2004 OPV was used for routine immunisation in UK, both OPV and IPV provide individual immunity, OPV reduces the frequency of symtpomless excretion of wild virus and hence better for community
Current polio vaccine (IPV) is killed, made from polio virus strains

Question 19

Haemophilus influenzae type B (bacterial)

Answer 19

Spread by droplet infection, causes bacterial meningitis, septicaemia and death
Vaccine introduced in 1992, following vaccine cases of HiB in children under 5 years fell by 98%

Question 20

HiB vaccine- subunit

Answer 20

Vaccine against Hib first produced in 1970s, effective inchildren >18 months
Conjugated HiB vaccnes linked capsular polysaccharide coat to proteins improved vaccine immunogenicity, particularly in under 1yrs
Hib conjugate vaccine introduce in 1992 and now part of 5 in 1 vaccine