L12 - Immunisation Flashcards
What is passive immunity?
Immunity produced by the transfer to one person of antibodies that were produced by another person. Protection from passive immunity diminishes in a relatively short time, usually a few weeks or months
What is active immunity?
The immunity which results from the production of antibodies by the immune system in response to the presence of an antigen
Exploits “immunological memory”
Secondary vs. primary response
Faster to develop
Greater in magnitude
May be qualitatively better (e.g higher affinity antibody)
What is the most effective antibody?
IgG
What is herd immunity?
Immunisation can protect:
• The individual
• The population – disease declines in majority of population is immune
Thresholds for different diseases
RO is the number of people in an unprotected population an infected person can transmit the disease to
Threshold is the percentage of the population that needs to be vaccinated in order to protect the entire population
Measles is extremely contagious and can spread through the air so has a high RO so needs a high threshold
Measles
A highly infectious viral disease; patients develop a rash and a fever
Serious complications can occur:
– Ear infection, which can lead to hearing loss
– Pneumonia, particularly in young children
– Sub-acute sclerosing panencephalitis (SSPE): a rare but fatal complication involving the CNS
Herd immunity & measles
MMR vaccine introduced in 1988
Need 83-94% of population immune to prevent outbreaks
1998 paper from Wakefield and colleagues linked MMR vaccine to autism
The paper was subsequently retracted but bad publicity resulted in a decline in uptake of vaccination and outbreaks are occurring
When has a country eliminated a disease?
A country has ‘eliminated’ the disease when it has stopped it freely circulating for at least three years
Requirements for an effective vaccine
- Safe
- High level of protection
- Long-lasting protection
- Right type of response
- Low cost
- Stable
- Easy to administer
- Minimal side-effects
What are the 5 types of vaccine?
Inactivated
Attenuated
Subunit
Toxoid
Conjugate
Inactivated vaccines
Dead/inactivated organisms
Have lost disease producing capacity
e.g. Salk polio vaccine (parenteral injection)
Attenuated vaccines
Live but virulence disabled
Attenuation takes an infectious agent and alters it so that it becomes harmless or less virulent
Examples: • Vaccinia (smallpox) • Sabin (polio) • MMR (measles, mumps & rubella) • BCG (tuberculosis)
Pros of live vaccines
- Single dose effective
- May be given by natural route
- May induce local and systemic immunity
- May induce right type of response
Cons of live vaccines
- Reversion to virulence
- Possibility of contamination
- Susceptible to inactivation
- Causes disease in immunocompromised host
The global polio eradication initiative
In 1988, the World Health Assembly (WHA) voted to launch a global goal to eradicate polio via high routine coverage with 3 doses of oral polio vaccine
- 1988: Endemic in >125 countries
- 2016: Endemic in 3 countries: Afghanistan, Pakistan and Nigeria
- Children affected by polio reduced from 1000 per day in 1988 to about 5 per day in 2006
- 99% eradicated
What is polio caused by?
Caused by an enterovirus, spread through faeco-oral route
Member of the picornaviridae: positive sense RNA, translated into a large polypeptide which is cleaved post-translation
What is a subunit vaccine?
A fragment of a pathogen, typically a surface protein, that is used to trigger an immune response and stimulate acquired immunity against the pathogen from which it is derived
Subunit vaccines need to have an antigen otherwise the B cells cannot recognise the infection
Examples: • Hepatitis B • Diptheria • Tetanus • Pneumococcal
What is a toxoid vaccine?
Toxoid vaccines contain a toxin or chemical made by the bacteria or virus. They make you immune to the harmful effects of the infection, instead of to the infection itself
Examples:
• Diphtheria
• Tetanus
What are conjugate vaccines?
Conjugate vaccines combine a weak antigen (polysaccharide) with a strong antigen (proteins) as a carrier so that the immune system has a stronger response to the weak antigen
Converts TI-2 polysaccharide antigen to a TD form
Allows young children to respond
Examples:
• Hib (Haemophilus influenzae type b)
• MenC (meningococcus type C)
• Pneumococcal conjugate vaccines (Prevnar 13®)
What is reverse vaccinology?
Whole genome screening to identify proteins that could be used as vaccines
Approach used to develop vaccine against Neisseria meningitidis group B
What are adjuvants?
Immunology’s ‘dirty little secret’
A substance administered with an antigen to promote the immune response
How do adjuvants enhance the immune response?
By providing a “depot”
By immunostimulatory properties
How do adjuvants act?
- Activate dendritic cells via TLRs or NLRs
- Cause release of endogenous danger signals
- Promote antigen uptake by dendritic cells
- Stimulate release of chemokines/cytokines
- Promote ‘cross-presentation’ of exogenous antigens by class I
