Vaccines Flashcards
what is variolation?
Variolation: Pus taken from a smallpox blister and introduced via a scratch to an uninfected person to confer protection.
- Practiced in Africa and Asia for centuries before first reports in Europe
how was variolation popularised in Europe?
- Variolation in Europe was popularised by Lady Mary Wortley Montagu in the early 1720s, after she witnessed the practice in Turkey.
- Tested on prisoners who were given freedom in return – some of the first clinical trials
- Lady Mary’s children were inoculated and also members of the royal family
who is Onesimus and what did he do?
- Onesimus, an enslaved African, introduced the principles of smallpox inoculation (practiced in sub-Saharan Africa) to his master, Rev Cotton Mather.
- Promotion of inoculation saved many lives during an outbreak in Boston in 1721 (6 out of 280 inoculated died; 844 out of 5,889 non-inoculated).
what did Edward Jenner do in 1796?
Developed the principles of vaccination:
- infected a boy with cowpox, then infected the boy with smallpox, and the boy didn’t get smallpox
Found that infection with cowpox provides protective immunity without risk of significant disease
why did Jenner’s cowpox inoculation against smallpox work?
- Cowpox virus and smallpox virus share antigens
- Cowpox virus stimulates an immune response that cross-reacts with smallpox antigens – protection against human disease
- Vaccination primes adaptive immune response to particular antigens so first infection produces a secondary response
what is the main goal of vaccination?
generation of long-lasting and protective immunity
what are the 2 key aims of vaccination to generate immunity?
Aim 1: Eradicate disease e.g. smallpox (which caused 400 million deaths in 20th century) officially eliminated in 1979
Aim 2: reduce incidence/transmission of disease
what factors favour global eradication of infectious diseases?
- disease is limited to human - no reinvasion by microbe from animal host
- no long-term carrier state - no reinvasion
- few unrecognised clinical cases - surveillance of incidence is possible
- one or few serotypes - a single vaccine is adequate
- vaccines for smallpox are stable, cheap and effective - programme can be worldwide and is cost effective, so likely to be undertaken
what is the impact of vaccination?
Great reduction in many diseases since vaccination introduced
- e.g. Measles vaccine (MMR) saved 17M lives since 2000
why is herd immunity important?
- For infections spread by person-to-person contact, risk of disease to an unvaccinated person dramatically reduced if 80 – 95% population vaccinated.
- Herd immunity only for disease spread by person-to-person contact e.g. tetanus
- % population that need to be vaccinated depend on how transmissible infection is e.g. higher for measles and Covid
how do vaccines confer protection?
via the induction of antibodies:
- Vaccine is injected into muscle and taken up by dendritic cells
- Vaccine is transferred to nearest draining lymph node to activate T cells (CD4 and CD8)
- B cells will differentiate to plasma and memory cells to generate an immune response
- Memory is generated
what is neutralising antibody?
Antibodies that coat a pathogen can stop the pathogen sticking to host cells - this is called neutralising immunity as you don’t get an infection at all
what are the key features of effective vaccines?
- Safe – vaccine must not itself cause illness or death
- Protective – vaccine must protect against illness resulting from exposure to live pathogen
- Gives sustained protection – protection must last for several years
- Induces neutralising antibody – some pathogens infect cells that cannot be replaced (e.g. Polio virus infecting neurons), so neutralising antibody is essential to prevent such infection
-Stop the infection occuring in the first place and prevents cellular damage - Induces protective T cells – some pathogens, mainly intracellular, are more effectively dealt with via cell-mediated responses
- Practical considerations – low cost per dose, biological stability, ease of administration, few side effects
what are the 3 main types of vaccine?
- Attenuated pathogen - Virulence reduced so causes mild infection
- Living – can replicate to an extent - Killed pathogen – Unable to replicate, fixed with formaldehyde
- Non-living - Subunit – Molecular component(s) of pathogen
- Non-living
what are the features of living vaccines?
- Preparation – attenuation (not always possible)
- Administration – may be natural e.g. oral - single dose
- Mimics real infection e.g. Polio vaccine
- Adjuvant – not required
- Safety – may revert to virulence – some danger
- Unsuitable for immunocompromised
- Requires cold storage – not good in tropical countries
- Cost = low
- Duration of immunity = years
- Full immune response: IgG, IgA, cell mediated (cytotoxic T cells for viral infection)
