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PGZ2024 Case summary (Disease and prevention module cases summary)

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This document is an indepth summary of all answers to learning goals of all cases in the PGZ2024 module (disease and prevention). It saves you the time of reading the whole literature as it includes all what you need to understand for passing the exam. Good luck!

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pgz2024
case summary
answers to learning goals
disease and prevention module
exam summary for cases in pgz2024

➔Case 1: Immunity and Vaccinations:

Immunity → the ability of the human body to tolerate the presence of (pathogens) material
indigenous to the body and to eliminate foreign substances.
- 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 involved the production of:
1. Protein molecules (immunoglobulins or antibodies) by B-lymphocytes
2. Specific cells, including T-lymphocytes (also known as cell-mediated
immunity)

How the vaccine works in the body to cause the immunity:
- They do this by introducing something called an antigen into the body, which imitates
an infection and primes the immune system to respond. → that way if we encounter
certain disease-carrying organisms, known as pathogens - in the future, our body already
has a plan of attack (has the antibodies)

Role of:
- B-Lymphocytes → create a protein called an antibody. These antibodies bind to
pathogens or to foreign substances, such as toxins, to neutralize them. Example: an
antibody can bind to a virus, which prevents it from entering a normal cell and
causing infection.
- T-Lymphocytes → T cells wipe out infected or cancerous cells. They also direct the
immune response by helping B lymphocytes to eliminate invading pathogens.

Types of Immunity:
1. Passive immunity:
- Production 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.
- Most common form of passive immunity → that which an infant
receives from the mother. Passive immunity can also be acquired through
the transfusion of blood products.

2. Active immunity:
- Protection produced by a person’s own immune system. Immune
system is stimulated by an antigen to produce antibody-mediated and
cell-mediated immunity.
- Active immunity lasts for many years, often for a lifetime

, - Ways of acquiring active immunity:
1. To survive infection without the disease-causing form of the
organism. When people recover from an infectious disease, they
will have a lifelong immunity to that disease
2. Another way to produce active immunity is by vaccination.

Many factors may influence the immune response to vaccination:
- Presence of maternal antibody
- The nature and dose of antigen
- The route of administration
- The presence of an adjuvant
- Host factors, such as: age, nutrition, genetics and coexisting disease

Classification of Vaccines:
Their characteristics are different and determine how each type is used:
1. Live, attenuated:
- Derived from “Wild” viruses or bacteria. These wild viruses or bacteria
are attenuated (weakened) in a lab. Example: the measles virus used as a
vaccine today was isolated from a child with measles disease in 1954.
- To produce an immune response, live, attenuated vaccines must
replicate in the vaccinated person. These vaccines do not cause the
disease and if they do it is a milder form than the natural disease.
- The immune response to a live, attenuated vaccine is identical to that
produced by the natural infection because the immune system does not
differentiate between an infection with a weak vaccine and an infection
with a wild virus.
- A live,attenuated vaccine may cause severe or fatal infections as a result
of uncontrolled replication of the vaccine virus or bacteria. → this
occurs only in persons with a weakened immune system (e.g, from
leukemia)
- One dose can be enough.

2. Inactivated:
- Inactivated vaccines are not live and cannot replicate. These vaccines do not
cause the disease, even if an immunodeficient person.
- Inactivated antigens are not affected by circulating antibody than are live
antigens, so they may be given when antibody is present in the blood
- The immunity provided by inactivated vaccines are NOT as long-lasting as that
obtained from live, attenuated vaccines.
- Multiple doses over time → are needed to obtain ongoing immunity.

,Herd immunity:
- “Herd immunity” or “herd protection” refers to the resistance of a group attacked by a
disease because of the immunity of a large proportion of the members and the consequent
lessening of the likelihood of an infected individual coming into contact with a
susceptible individual.
- Based on the “herd immunity” concept → elimination of an infectious agent from a
population can be achieved even if it is not possible to vaccinate the entire
population.
- The idea of herd immunity is based on the relationship between the transmission
dynamics of infectious agents and population immunity.

How to achieve it:
- Herd immunity → achieved by mass immunization against infectious diseases that are
transmitted directly from person to person (e.g. measles), especially those for which
humans are the only reservoir or one of the important reservoirs of infection.
- Herd immunity CAN NOT be achieved when infectious are not transmitted from
person to person and humans are not an important reservoir of infection (e.g.
tetanus)
- Herd immunity concept → The simple “herd immunity threshold” concept assumes
that vaccines induce solid immunity against infection in a randomly mixing
population. → the key determinants of herd immunity are based on the basic
reproduction number R0 (the average number of others individuals each infected
individual will infect in a population that has no immunity to the disease)
- In order to eliminate or eradicate an infection, the proportion of immune
individuals in a population must be equal to or greater than (1-1/R0)

IMP Extra Aspects about Herd immunity:
1. An ideal vaccine should be highly immunogenic and would confer solid
immunity against infections to all recipients. BUT, if a vaccine does not
grant solid immunity, the threshold level of vaccination required to protect
a population will increase.
2. In a heterogenous population, the “R0” in the formula should also
account for the factors that affect the interaction of various groups in a
population. → groups that are highly interconnected will dominate
transmission resulting in a higher value of R0, requiring a large
vaccination threshold.
3. Non-random vaccine uptake: Simple results will no longer follow if
vaccination converges depending on the risk behaviors of the groups.
Example: if every high-risk person in a population infects four individuals

, and every individual in low-risk group infects only one person, outbreaks
in theory can most effectively be prevented by vaccinating 75% of the
high-risk group. But problems will arise if the high-risk persons are least
likely to be vaccinated or if they mix with unvaccinated individuals
homogeneously.
4. “Freeloaders” - people who wish that everyone else around them is
vaccinated except themselves create a special scenario. They take the
advantage of herd immunity without taking the trouble of getting the
vaccine.

Role of vaccination programs:
- The overall aim of a national vaccination program is to protect the population from
vaccine preventable diseases and reduce the associated mortality and morbidity. -
- Reduce burden on the health system
- Reduce disease spread, preventing complications and deaths from vaccine preventable
diseases.

Role of social media in decision making for vaccines:
- Web 2.0 → internet applications that enable users to create and upload new
content, comment on existing content and share content with other users, e.g.
discussion boards, web blogs, and social media websites such as facebook →
enables two-way and multi-way communication
- Actors in Web 2.0:
1. The decision maker (referred to as the user) as the receiver of information
obtained on the internet
2. Health-communicators who use Web 2.0 to disseminate evidence-based facts
about vaccination as well as messages providing support for recommended
vaccinations e.g. via social media
3. Anti-vaccination activists who use Web 2.0 to disseminate messages, facts and
beliefs that oppose some or all recommended vaccinations

IMP: Decision process in the individual has 3 stages:
1. Pre-decisional phase: where individuals consider their options, usually to either
vaccinate within the recommended time frame, with delay or not at all.
2. Decisional phase: individuals here evaluate potential outcomes of alternative
actions (such as vaccinating or not) based on the obtained information. Current
theories of health behavior assume that individuals must first perceive themselves
as being at risk before they take proactive action.
- Risk perception: has been conceptualized as a combination of one's
beliefs about the likelihood of being affected by a negative event and

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