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PGZ2024 Disease and Prevention: samenvatting alle taken
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Samenvatting van alle taken die onderdeel zijn van het blok PGZ2024.
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Taak 1: VaccinationVaccination is a way to produce active immunity. Vaccines contain antigens that stimulate the immune system
to produce an immune response.
There are two basic types of vaccines.
1. Live, attenuated (verzwakt): live vaccines are derived from “wild” viruses or bacteria. These wild
viruses or bacteria are attenuated (weakened) in a laboratory (the measles virus).
2. Inactivated: inactivated vaccines are not alive and cannot replicate. These vaccines cannot cause
disease, even in an immunodeficient person (a very vulnerable person).
Inactivated vaccines include:
- whole-cell inactivated vaccines (e.g., polio, hepatitis A, and rabies vaccines) à bacteria or viruses that
have been killed through a physical or chemical process.
- subunit vaccines (e.g., influenza and pneumococcal vaccines) à a portion of the bacteria or virus.
- toxoids (e.g., diphtheria and tetanus toxoid) à are made using inactivated toxins produced by bacteria.
- recombinant vaccines (e.g., hepatitis B, human papillomavirus [HPV], and influenza à are produced
by recombinant DNA technology.
Good to know that there are types, but you don’t have to come up with them
Immune system
The immune system develops a defense against antigens, which are substances that can stimulate the immune
system. This defense is known as the immune response and usually involves the production of:
- Protein molecules (immunoglobulins or antibodies, the most important component of humoral
immunity) by B lymphocytes (B cells)
- Specific cells, including T lymphocytes (also known as cell-mediated immunity)
2 basic mechanisms: passive and active immunity.
- Passive immunity is protection by antibody or antitoxin produced by one animal or human and
transferred to another. Passive immunity provides immediate protection against infection, but that
protection is temporary.
Passive immunity can also be acquired through the transfusion of blood products.
Example: when an infant receives antibodies from the mother. An infant will then have the same type of
antibodies as the mother. The infant is then protected from certain diseases within the first few months after
birth.
- Active immunity is protection produced by a person’s own immune system. The immune system is
stimulated by an antigen to produce antibody-mediated and cell-mediated immunity. Unlike passive
immunity, which is temporary, active immunity usually lasts for many years, often for a lifetime
o A way to acquire active immunity is by surviving an infection.
Immunologic memory = the fact that protection persists for many years after infection. After
the immune system has been exposed to an antigen, B memory cells continue to circulate in
the blood and when re-exposed to the antigen, the memory cells begin to replicate and rapidly
produce antibodies to restore protection.
o Another way to produce active immunity is by vaccination. The recipient is not subjected to
the disease and its potential complications. A vaccine contains antigens that stimulate the
immune system to produce an immune response.
, Herd immunity
Herd immunity = the resistance of a group attacked by a disease, due to the
immunity of a large proportion of its members and the consequent reduction
in the likelihood of an infected individual coming into contact with a
susceptible (vatbaar) individual.
Herd immunity can be achieved by mass immunization against infections
that are transmitted directly from person-to-person (e.g., measles, pertussis,
or influenza)
Other factors that infect herd immunity: how well the vaccination uptake is
in different population groups (bible belt).
Vaccination degree depends on the disease.
Theoretical developments in the concept of herd immunity
1. An ideal vaccine should be highly immunogenic and would
confer solid immunity against infection to all recipients.
However, when a vaccine does not grand solid immunity, the
threshold level of vaccination required to protect a population
will increase.
2. In a heterogeneous population, the R0 should account for the
factors that affect the interaction of various groups in a
population. Groups that are highly interconnected will
dominate transmission leading to a higher value of R0.
3. Simple results will no longer follow if vaccination coverage
differs depending on the risk behaviors of the groups. For example, if every highrisk person in a
population infects four individuals (R0= 4, so vaccine coverage = 75%) and every individual in
low-risk group infects only one person (R0=1, so vaccine coverage = 0%), outbreaks in theory can,
most cost-effectively, be prevented by vaccinating 75% of the high-risk group
4. Freeloaders – people who wish everyone else is vaccinated except themselves, they take advantage
of herd immunity without taking the trouble of getting the vaccine.
Effective transmission:
Contagiousness (pathogen) and susceptibility (host)
- Contagiousness (besmettelijkheid)
Basic reproductive rate R0
R0 = B x c x D
B = chance of transmission
c = number of newly infected/time
D = duration of infectious period
Infection will: disappear if R<1
become endemic if R=1
become epidemic if R>1
- Susceptibility (vatbaarheid)
o Personal immunity
o Herd immunity
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