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Problems with Vaccines
Not all vaccination programs are completely successful in eradicating a disease. One
that was, is the smallpox vaccine. This disease was caused by the variola virus. 12-30%
of sufferers died while many who recovered were often blinded. In 1967, WHO (the
World Health Organisation) vaccinated more than 80% of the world’s population who
were at risk and when a case was reported all
possible contacts in the area were vaccinated
(ring vaccination).
Eradication in rural areas proved a challenge, but
the last case occurred in Somalia in 1977 and in
1980, WHO declared the world free of smallpox.
Reasons for the success of the vaccine
included:
1. The variola virus did not mutate and change its antigens.
2. It was made from a live harmless strain of a similar virus, so it mimicked a
natural infection, multiplying and continually presenting the immune system with
a large dose of antigens.
3. It could be freeze-dried and kept for six months aiding distribution.
4. Infected people were easy to identify.
5. It was easy to administer and the disease did not linger in the body.
6. Smallpox does not infect animals.
Less successful vaccination programs have included those against measles, tuberculosis,
malaria and cholera.
Measles
This disease offers the promise of eradication if worldwide surveillance was followedup by vaccination.
However, so far it has failed because:
1. A poor response to the vaccine has been shown by some children, who need
boosters.
2. High birth rates and shifting populations make
following-up cases difficult.
3. Migrants and refugees may spread the disease.
4. Measles is highly infective and 95% immunity of a
population is required to prevent transmission.
5. The vaccine only has a 95% success rate.
Problems with Vaccines
Tuberculosis
This disease was once thought to have been eradicated, but is actually showing a
resurgence.
The reasons include:
1. Some TB bacteria are resistant to drugs used to treat
them because they can mutate.
2. AIDS can allow TB to infect an individual due to their
compromised immune system.
3. Poor housing and homelessness lowers peoples' natural
resistance.
4. There have been breakdowns in the TB control program.
5. It is actually caused by two different bacteria with two different antigens,
which can live inside human cells, making them hard to fight.
6. It can be carried in cattle.
Malaria
This is a disease caused by Plasmodium, a
protoctist (eukaryotic) that has hundreds or even
thousands of different antigens. It also has three
different stages in its life cycle, meaning that
developing a vaccine is incredibly challenging and
has not yet been achieved.
Cholera
This disease is caused by Vibrio cholerae, which can live in the
intestines where antibodies - produced by vaccines that are
injected - cannot get to it. An oral vaccine is in development.
Sickle Cell Anaemia
This is not caused by an infectious agent, it is a genetic disorder. There is no
antigen to produce antibodies against. It cannot be prevented using vaccination,
but the use of bone marrow transplants has been shown to help in some cases.
Problems with Vaccines
Read through the text and indicate whether the following
statements are true or false:
The variola virus is able to mutate into many different
forms.
The smallpox vaccine was not affected by transport and
storage.
It was difficult to know who was suffering from small pox.
Some children need to have the measles vaccination more
than once.
There is a small chance of contracting measles even if you
have had the vaccination.
There are fewer TB cases now than ten years ago.
There is close correlation between the incidence of AIDS
and the incidence of TB.
TB is caused by one strain of bacteria.
Other animals as well as humans can be affected by TB.
Malaria is caused by a prokaryotic pathogen.
Plasmodium species present many different antigens.
Oral vaccines are able to enter the digestive system.
Genetic disorders are caused by pathogens.
Sickle cell anaemia can be treated by vaccination.