Diseases preventable by traditional vaccines
Polio is a viral infection that can result in permanent
More than half of all cases are in children
under age three but anyone can be affected. Poliovirus is spread by person-to-person
contact, and contact with infected faeces or with secretions from the nose or
mouth. The virus establishes itself in the intestines, from where it can enter
the blood and invade the nervous system. In severe cases, the brainstem can be
infected, leading to respiratory failure and death. As the virus multiplies it
destroys nerve cells that activate muscles, particularly in the legs, so that
these muscles no longer function.
There is no
cure for polio and immunization is the only effective way to prevent the disease.
Since 1955, when the first effective polio vaccines
were introduced, the disease has been practically eliminated as a public health
problem in the industrialized countries. In 1988 the World Health Assembly resolved
to eradicate polio globally by the end of the year 2000.
12 years, thanks to the efforts of national governments working with WHO, Rotary
International, UNICEF and other partners, the number of reported cases fell markedly
from an estimated 350,000 to approximately 3,500 in 2000, according to WHO.
polio is within sight of eradication worldwide. Large parts of the world are polio-free,
including the WHO Regions of the Americas, Western Pacific, and Europe. However,
the fragility of the progress is reflected by recent outbreaks that have occurred
where immunization programmes have broken down because of war or other disruption.
During 2000, reservoirs of poliovirus infection in South Asia and West/Central
Africa are targeted for accelerated eradication activities.
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Diphtheria is a bacterial infection caused by the organism
Corynebacterium diphtheriae. The spread of infection requires close contact between
When an infected person coughs or sneezes, droplets
containing the bacteria may enter the nose or throat of another person. While
some people experience few or no symptoms, others develop infection in the throat
and respiratory tract which can result in obstructed breathing and death. Even
with treatment, one in ten affected persons dies of the disease. The infection
can also cause damage to the heart and nervous system. In tropical environments,
the skin can be affected.
A safe and effective
vaccine has long been available for diphtheria; it is usually given together with
vaccines against tetanus and pertussis
in the triple vaccine known as DTP.
3000 people, mostly children, die of diphtheria each year. There have been recent
epidemics of the disease in Russia and other Eastern European countries, and some
of those affected have been adults.
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Pertussis is caused by infection with
the bacterium Bordetella pertussis. It is spread by droplets and direct contact
and is highly contagious.
Each year, about 296 000 people,
mostly young infants, are killed by the disease worldwide, and at least 45 million
suffer from the illness with prolonged and exhausting bouts of coughing that may
continue for up to 3 months. Some children also suffer seizures and neurological
In recent years there have been reported
increases in the incidence of pertussis, including in several industrialized countries.
Immunity to infection is not permanent, even after infection with B. pertussis.
This partly explains the number of cases observed in adolescents and adults in
Vaccines based on whole killed
B. pertussis bacteria (known as "whole-cell vaccines") have been used effectively
and safely for several decades to prevent infection.
but usually mild, adverse reactions associated with these vaccines, such as fever
and localized side effects (redness, swelling and pain at the site of injection)
and a fear of extremely rare but serious neurological events, reduced public acceptance
of these vaccines in the 1970s in some countries, and led to the development of
a new generation of vaccines that contain components of the bacterium instead
of all of it. These products, known as "acellular" vaccines, provoke fewer of
the frequent mild-to-moderate reactions seen with the whole-cell vaccines, while
severe adverse effects are equally rare in both types of vaccine. The best acellular
vaccines are as effective as the best whole-cell vaccines. Acellular vaccines
are considerably more costly, however, and therefore whole-cell vaccines continue
to be the most widely used. Both whole-cell and acellular vaccines can be given
in combination with tetanus and diphtheria vaccines.
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Tetanus is caused by infection with a bacterium, Clostridium tetani, which is
present in the soil, in animal dung and in faeces and enters the body through
The bacterium produces a toxin which can make
skeletal muscles unusually rigid, and may result in spasms. Because these spasms
may affect the facial muscles, tetanus is sometimes known as lockjaw. Ultimately,
breathing may become difficult or impossible, resulting in death. Neonatal tetanus,
which affects newborn babies, usually results from unsafe delivery in unhygienic
conditions or without skilled birth attendants. Unsterile cutting and care of
the umbilical cord is a frequent source of infection. As with many other infectious
diseases, poverty greatly increases families vulnerability.
There are an estimated 200 000 deaths from neonatal tetanus each year. However
the total number of tetanus deaths is much greater because mothers, older children
and others can also be affected. WHO estimates that there are some 509 000 deaths
altogether each year. Safe and effective vaccines against tetanus has been available
for decades and are usually given with those for diphtheria
the World Summit for Children in 1993 the WHO has been working to eliminate neonatal
tetanus as a public health problem. Strategies that governments can employ to
achieve this goal include:
- Ensuring that
all pregnant women receive at least two doses of tetanus vaccine
safe clean delivery for all women.
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Measles is a serious
illness caused by a virus of the paramyxovirus family. It is a highly contagious
infection, spread by droplets, with an incubation period of between 7 and 18 days.
Infected individuals may suffer fever, cough, rash,
conjunctivitis, diarrhoea, ear infections and pneumonia. A less frequent but serious
consequence of infection is encephalitis, or inflammation of the brain.
kills an estimated 777,000 people, most of whom are children, worldwide each year
and also causes permanent disabilities for some of its survivors, including blindness,
deafness and brain damage. Complications of the disease are much more common in
low-income countries, and in malnourished children, than in industrialized countries.
Although there is no specific treatment for measles, the number of cases of illness
that prove fatal (between 3 per cent and 5 per cent in developing countries, and
up to 30 per cent in some situations) can be reduced by effective case management,
including oral rehydration therapy and the use of vitamin A supplements.
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