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4.4 Vaccines
How vaccines work
What are the known vaccines? the beginning of vaccination, as well as the
Diseases preventable by vaccination are doses, are therefore not random but based on
infectious ones (viral or bacterial). Examples are certain tried and tested criteria.
vaccines against rotavirus and meningococcus An example of this review is the tetanus
B, which are tested, safe, internationally vaccine that used to be given every ten years,
approved vaccines, but are not mandatory in but the period was extended lately, because it
many countries. There are also vaccinations was realised that people still had immunity to
that are internationally required., i.e., vaccines tetanus.
that must be administered in travellers’
appointments, i.e., in international vaccination How long does a vaccine take to be
centres when we go to certain countries. prepared?
Yellow fever is an endemic disease in some The same time as other drugs (medicines)
countries and since we can only enter these which are not vaccines. The rules of preparation
countries by taking the vaccine, there is an are established at international level and go
obligation to take it. Hepatitis A is a vaccine through several phases. A pre-clinical phase
that, in a lot of countries, is administered to corresponds to the research phase (laboratory).
people who travel to certain areas of Africa Molecular studies, biochemical studies and
or some South American countries, but not to characterisation are necessary. Then studies
all. It is known that hepatitis A was a common on cellular lines and later on animal models.
disease in the 1960/70s, and people who were Then moving on to the clinical phase, which
born until the 1960s do not need to take this involves humans and also has 3 to 4 phases.
vaccine, because they already had the disease.
However, for those who were born later, it is The clinical phase consists of the 1 phase
st
recommended they get vaccinated when they performed initially in some individuals, the 2
nd
are travelling. phase performed in selected individuals and
the 3 phase, a true clinical trial. In this phase,
rd
Across Europe and other parts of the world there is a drug and there is a placebo, and
national vaccination programs exist, whose they are administered “blindly”. The doctors do
schemes reveal the age at which vaccines are not know to which patient they administer the
normally administered. There are variations drug in order to assess their response and if it
between different countries. There are specific is the intended one. The question of phase 3
reasons though, why vaccines are given at studies not being representative is not correct,
certain ages and doses. For example, VASPR, since the regulatory authorities, both American
vaccine against measles, parotitis and rubella. and European, are extremely strict in the
It is often given at 12 months because it has requirements of the sample being studied.
a component, ovalbumin, which can cause Randomised trials are mandatory and must be
allergic reactions. Children at 12 months of compared it not only with the placebo, but with
age have already started eating eggs, so it is the drug.
already known if they are allergic to it. Allergic
reactions to ovalbumin are rare. The date of There can be a 4 phase. It is the one where the
th
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