Vaccines Flashcards
What is passive immunisation?
Passive immunity is a short-term immunity which results from the introduction of antibodies from another person or animal
What’s a limitation of passive immunisation?
only humoral (antibody) mediated
What’s an advantage of passive immunisation?
- Gives immediate protection
- Effective in immunocompromised patients
What are disadvantages of passive immunisation?
- short-lived
- Possible transfer of pathogens
- “Serum sickness” on transfer of animal sera
What are some examples of passive immunisation?
- Specific Immunoglobulins (Ig)
- Human Normal Immunoglobulin (HNIG)
- Convalescing serum eg., SARS Co-V2
What is a vaccine?
Antigenic substance prepared from the causative agent of a disease
What are 2 forms of active immunisation?
- Non-Living Vaccines (whole killed and toxoids)
- Live Attenuated Vaccines
What is the whole microbe vaccine?
- Bacteria or viruses grown in vitro and inactivated using agents such as formaldehyde or Β-propionolactone
- Formaldehyde stops bacteria from being infectious
What is a non-living vaccine?
- do not cause infection
- antigens contained in it induce an immune response that protects against infection by non-self antigen recognition
What are cell-free toxoids?
Can be non-living vaccines
What are some problems with whole killed vaccines?
- The organisms must be grown to high titre in vitro (viruses and some bacteria difficult/expensive to grow in the lab)
- Whole pathogens can cause excessive reactogenicity (i.e. adverse reactions, excessive immunological responses)
- Immune responses are not always close to the normal response to infection, e.g. no mucosal immunity, no CD8 Tc responses
- Usually need at least 2 shots
What are some examples of bacterial whole killed vaccines?
- Diphtheria - formaldehyde treated toxin - rendered a non-toxic “toxoid”
- Tetanus - toxoid
- Pertussis (whooping cough) - killed whole bacteria (Bordetella pertussis) given with the two above as DTP
- 3-doses
- UK has now moved to acellular pertussis
(aP), not whole cells
- Cholera - heat-killed bacteria
What are some examples of viral whole killed vaccines?
- Polio vaccine (Salk) - inactivated virus-IPV
- Influenza vaccine - inactivated virus
- Hepatitis A vaccine - inactivated virus
- Rabies vaccine - inactivated virus
- SARS-Co-V2 (Valneva) - inactivated virus
How do viral vaccines work?
The organisms replicate within the host and induce an immune response which is protective against the wild-type organism but does not cause disease
Is using whole killed vaccines or dead ones better?
Using whole virus or bacteria usually gives better protection as can replicate rather than dead ones
What is attenuation?
- Where an organism is cultured in such a way that it does not cause disease when inoculated into humans
- It has lost its pathogenicity but retains its antigenicity – (i.e. shape)
What are the advantages of live attenuated vaccines?
- Immune response that follow real infection because its not fixed – no shape change, more closely mimics
- Better immune response so doses are required, so the scale of in vitro growth needed is lower
- Route of administration may be more favourable (oral)
- Fewer doses may be required to provide protection
What are problems with live attenuated vaccines?
- Often impossible to balance attenuation and immunogenicity
- Reversion to virulence (harmfulness)
- Transmissibility
- Live vaccines may not be so attenuated in immunocompromised hosts
What are bacterial examples of attenuated vaccines?
- Bacille Calmette-Guérin (BCG): Mycobacterium bovis grown over many passages in vitro
- Gives some protection against TB (tuberculosis)
- Salmonella typhi: temperature sensitive strain given orally
What are viral examples of attenuated vaccines?
- Poliomyelitis (Sabin) - widely used to bring polio to the brink of eradication
- Vaccinia virus - used in billions of doses to eradicate smallpox due to cross-reactivity between itself and the variola virus
- Measles, Mumps and Rubella - 3 given together as MMR
What are examples of some pathogens lacking vaccines?
- HIV
- Malaria
- Herpes Simplex Virus
etc
Why might some pathogens not have vaccines?
- Pathogen too difficult to grow
- Killed pathogen not protective (shape change)
- Impossible to obtain attenuated and suitably immunogenic strain
- Too many strains causing disease etc.
What are some new vaccine approaches?
- Recombinant Proteins
- Synthetic Peptides
- Live Attenuated Vectors
- mRNA Vaccines
- Polysaccharide-Protein Conjugates
What are the stages of vaccination?
- Engage the innate immune system
- Danger signals that activate the immune system, triggers such as molecular fingerprints of infection – PAMPs (pathogen associated molecular patterns)
- Engage TLR receptors
- Activate specialist APC (antigen presenting cell)
- Engage the adaptive immune system
- Generate memory T and B cells
- Activate T cell help
