vaccinations

• life expectancy has increased due to improvement in health of young people, less deaths due to communicable diseases
• vaccines contain antigens
• expose immune system to antigen without causing disease
• vaccination 


  refers to having received the vaccine (getting injection)
• immunisation 


  means receiving and becoming immune to a disease, as a result of being vaccinated
• vaccines induce active immunity (and memory) to that acquired by exposure to natural infection (without risk of disease)
• immunological memory allows 


  rapid recognition and response to infection, prevents or modifies effects of disease
• measles vaccine 


  annual number notified cases and death (vaccine introduced in 1968)
• good vaccine

  • elicit response without causing disease
  • safe
  • stable (no need for cold chain)
  • cost
  • ease of administration (oral preferred)
  • long term protection (single dose is good enough)
  • interrupt spread of infection
• types of vaccines

  • live (artificially reduced virulence)
  • inactivated (killed)
  • subunit vaccine -toxoid, surface protein, viral vector, DNA and RNA vaccines
  • passive immunotherapy
• Polio causes

  • paralysis of muscles
  • 1 in 200 infections result in irreversible paralysis
  • present in Afghanistan and Pakistan (endemic)
• polio spread through 


  faecal oral route
• serotypes 


  Brunhilde, Lansing, Leon
• polio disease caused by different serotypes, different antibodies produced so vaccine needs to provide immunity to all 3
• live attenuated viruses

  • inexpensive
  • easily administered
  • antibodies in blood prevent spread to CNS
  • mucosal immunity prevents viral replication in the gut
  • passive immunity of persons in close contact
  • life long immunity
• live attenuated viruses (disadvantages)

  • unable to give to pregnant or immunocompromised
  • could revert to virulent form
  • unstable vaccine
• killed vaccine (polio)

  • 3 serotypes -chemically inactivated
  • cannot cause circulating vaccine derived polio virus
  • antibodies prevent spread to CNS
• killed vaccine (disadvantages)

  • injection
  • no effect on viral replication in gut or viral transmission in stool
• inactive vaccine advantages

  • cannot cause infection
  • can be given to immunosuppressed and pregnant individuals
• disadvantages of inactive vaccine

  • less immunogenic
  • require booster
• adjuvant

  • carry vaccine antigen and slow its release
  • provoke local inflammatory response
• adjuvant example 


  aluminium hydroxide
• polio 


  type 2 and type 3 eradicated, type 1 only in 2 countries
• T cells can be used as immunotherapy
• toxoid vaccine (tetanus vaccine)

  • spores of tetanus are widespread
  • causes neurotoxins producing muscle spasms, start with lock jaw
  • seizures can be triggered
  • children are routinely offered tetanus vaccine
• surface protein vaccine (Hep B vaccine)

  • blood of infected, purify out protein
  • inactivate
  • risk of viral transmission
  • expensive
  • using DNA recombination technology now
• viral vector vaccine (SARS-CoV-2)

  • spike protein
  • gene sequencing
  • modified virus, so cells express spike protein
  • and body produces antibodies against spike proteins
• DNA vaccines

  • injecting nucleic acids encoding antigens
  • result in expression in situ and elicits immune response
  • delivered in plasmid

  concern about genomic incorporation could activate oncogenes
• several DNA vaccines licenced for veterinary use
• mRNA

  • encapsulated in lipid vesicle to protect
  • Moderna and Pfizer Covid19 vaccine first mRNA vaccines for mass immunisation in humans
  • encode full length or receptor binding domain of SARS-CoV-2 viral spike protein
  • requires careful long term storage
• primary failure 


  individual fails to make adequate immune response, to initial vaccination so infection is possible any time after vaccine
• secondary failure 


  individual makes adequate immune response initially, immunity wanes over time (feature of most inactivated vaccines, need booster)
• herd immunity

  • more immune individuals, less likely susceptible person comes into contact with person with infectious disease
  • prevents spread of disease and protects groups who cannot be vaccinated
  • disease spread is contained
• vaccine rates are declining because

  • vaccine hesitancy -reluctance or refusal to vaccinate despite availabilty of vaccines