Microbiology and Immunology 3820A Lecture Notes - Lecture 5: Sick Individuals, The Who, Poxviridae
18 Oct 2018
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LECTURE 5 STUDY NOTE – VACCINES
LEARNING OBJECTIVES
✓ Herd Immunity
✓ History of Vaccines
✓ Types of Licensed Vaccines
✓ Adjuvants
✓ Next generation vaccines
✓ Challenge with vaccination
MOST EFFECTIVE WAYS TO PREVENT INFECTIOUS DISEASES ARE
1. Prevent Transmission
o Blocking any of the steps in the chain of infection
o Vaccination are particularly important for those who are susceptible
2. Prevent Infection
o Vaccination to elicit immune protection in host
o If you are susceptible to the pathogen, you will get sick
WHAT ARE VACCINATIONS?
• Vaccination is the intentional exposure to pathogens in a form
that cannot cause an infectious disease
• Protect against pathogens that have a high morbidity and
mortality rate
PURPOSE OF VACCINATIONS
• For the recipient to develop long term immune protection against the pathogen
• Vaccinated person mounts a memory immune response to same pathogen → more protective
response
HERD IMMUNITY
• Protects susceptible individuals by stopping
transmission of a pathogen
o The risk of infection is reduced when the # of
individuals who can spread the pathogen is
reduced
• Let’s say you are immune to a particular pathogen… whether that be by natural/vaccine exposure, if
someone is transmitting the pathogen you are immune to, it will enter you and be destroyed
immediately
• You are indirectly protecting those around you
• Only effective when a sufficient # of people are immune
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• If you have 2 sick people in a population and majority of the people are HEALTHY but NOT IMMUNE,
the pathogen will be transmitted around very quickly
• If you increase the amount of people who have been vaccinated (in yellow) a “wall is formed around
the sick individuals and a wall around these who are highly susceptible to infection”
• Increased persons who are immunized = decreased amount of infection
WHEN CAN DISEASE OUTBREAKS OCCUR?
• Disease outbreaks can occur when immunity falls below a critical percentage in a population
EXAMPLE WITH MEASLES
• If one individual enters a room and has measles, that is going to spread to 12-18 individuals within
the room
• Herd Immunity Threshold: 92-94% of people must be vaccinated or have immunity against measles
in order to prevent the spread (HERD IMMUNITY)
BREACHING HERD IMMUNITY → BIGGEST THREAT TO VACCINATIONS
• The UK MMR vaccine controversy in 1998
• Andrew Wakefield claimed that he did studies which found MMR vaccines caused autism
• He RETRACTED THE PAPER 2 YEARS LATER
• Damage has already been done though and this is still an immense fear today
WHAT HAPPENED TO ANDREW WAKEFIELD?
• Brought to court and stripped of his medical licence
• He committed an elaborate fraud by faking the data
THE OTHER UNFORTUNATE VARIABLE THAT MADE THIS BELIEVABLE TO
CONSUMERS?
• Autism was known, but the diagnosis for it was not well established
• This was starting to change at that time of the MMR vaccination scandal
• The diagnosis for autism were getting better/clearer and as a result:
3
o An increased amount of autism cases were getting diagnosed at the same time the whole
MMR vaccination scandal was the hot topic
ANDREW WAKEFIELD’S STUDY SPARKED NEW MEASLES CASES/OUTBREAKS
• Immunization rates decreased and number
of infections increased
• Majority of people getting measles are
unvaccinated
• MMR reappeared because people were not
getting the vaccination they needed
• 2015 Disneyland outbreak → occurred in 1
day (189 from 24 states)
SEVERAL STUDIES THEREAFTER
• Have failed to support an association
between MMR vaccine and autism
• These studies used proper CONTROL groups which were lacking in Andrews Study
VACCINATIONS IN CANADA
• 1.5-3% of children in Canada have NEVER had a vaccination
• 20% of parents believe that vaccines are directly related/linked
to autism
• 37% of parents believe that a vaccine can cause the same disease
that it is meant to prevent
• Significant numbers of parents do NOT BELIEVE IN HERD
IMMUNITY
• 70% of parents are concerned about the potential side effects from vaccines
• A minority believe that homeopathy and chiropractic manipulations can eliminate the need for
vaccines
• Vaccine hesitancy is INCREASED (in Canada as well)
EXAMPLE → SMALL POX & POLIO
• Declared eradicated in 1980
• Polio initiative is global and is to be eradicated and began in 1988-present day
o World leaders get together on matters such as this
INTRODUCTION OF VACCINES IN USA AND DISEASE NOTIFICATION
• There is clear evidence that vaccinations actually reduce the incidence of disease
Document Summary
Most effective ways to prevent infectious diseases are: prevent transmission, blocking any of the steps in the chain of infection, vaccination are particularly important for those who are susceptible, prevent infection, vaccination to elicit immune protection in host. If you are susceptible to the pathogen, you will get sick. What are vaccinations: vaccination is the intentional exposure to pathogens in a form that cannot cause an infectious disease, protect against pathogens that have a high morbidity and mortality rate. For the recipient to develop long term immune protection against the pathogen: vaccinated person mounts a memory immune response to same pathogen more protective response. Herd immunity: protects susceptible individuals by stopping transmission of a pathogen, the risk of infection is reduced when the # of individuals who can spread the pathogen is reduced. If you have 2 sick people in a population and majority of the people are healthy but not immune, the pathogen will be transmitted around very quickly.
