Vaccine-Preventable Diseases: An Overview
Global statistics from eight vaccine-preventable
Annual cases (estimated)
Annual deaths (estimated)
Tetanus (including 215 000 neonatal)
Haemophilus influenzae b (Hib)
B actual deaths based on projections of future mortality resulting
from current annual infection rate
Source: WHO World Health Report 1999, and WHO
Department of Vaccines and Biologicals
Summary of Major Vaccine-Preventable
Polio is caused by a
viral infection (poliovirus) that invades the nervous system
and can cause paralysis in a matter of hours. One in 200
infections leads to paralysis (usually the legs) and its
effects are irreversible. Between 5 and 10 percent of patients
die when their breathing muscles are paralysed.
- People catch the virus through direct person-to-person
contact, through contact with infected secretions from the nose
or mouth or by contact with infected feces. The virus enters
through the mouth and nose, multiplies in the throat and intestinal
tract, and then is absorbed and spread through the blood and
to the spinal cord and brain.
- The virus begins to cause symptoms between
5 to 35 days (average 7 to 14 days) after infection. According
to the World Health Organization, it can strike at any age,
but over 50 percent of all cases involve children under three.
There is no cure for polio; immunization is the only way to
prevent the disease.
Diphtheria is an infectious
disease that spreads from person to person through respiratory
droplets from the throat via coughing and sneezing. The
disease normally breaks out 2 to 5 days after infection.
Two forms of diphtheria bacteria occur: one produces toxin
and the other does not. Damage is done by the toxin.
- The disease usually affects the tonsils,
pharynx, larynx and occasionally the skin. Symptoms range from
a moderately sore throat to toxic life-threatening diphtheria
of the larynx or of the lower and upper respiratory tracts.
This occurs because the disease results in the formation of
a membrane in the throat that may get so big it completely blocks
the larynx, causing death by suffocation.
- Other serious complications of diphtheria
involve diphtheric-myocarditis (toxic damage to heart muscles)
and neuritis (toxic damage to peripheral nerves) and can be
fatal - about 1 person in 10 (10 percent) still dies in spite
of treatment. Untreated patients are infectious for up to four
- Unless immunized, children and adults may
be infected repeatedly with the disease. The most effective
method of epidemic control is mass immunization of the entire
population. The most effective method of prevention is immunization
in early childhood, often followed by booster doses at school
cough) is a highly contagious bacterial disease involving
the respiratory tract and caused by infection with Bordetella
pertussis bacteria. It is transmitted through direct
contact with discharges from respiratory mucous membranes
of infected persons carried in the air. The bacteria invade
the nose and throat, the trachea, and the bronchial tubes
of the lungs, causing symptoms in about a week.
- The typical illness lasts 6 to 12 weeks,
starting with symptoms similar to the common cold and progressing
to spasms of coughing after 10 to 12 days.
- Worldwide, B. pertussis causes some
45 million cases of pertussis, 90 percent of which occur in developing
countries. Although pertussis may occur at any age, most serious
cases (including brain damage) and the majority of fatalities
are observed in early infancy, a time when pertussis is most severe.
Vaccines are the most rational approach to pertussis control -
if children are not immunized, they have an 80 percent chance
of contracting whooping cough before the age of five.
Measles is a highly
contagious viral illness characterized by a fever, cough
and spreading rash. For children, it is the most contagious
of the child killers. Caused by the paramyxovirus, it is
spread by droplets from the nose, mouth or throat of an
- The incubation period usually lasts 10
days (with a range from 7 to 18 days) from exposure to the onset
of fever. The disease is characterised by prodromal fever, conjunctivitis,
coryza, cough and the presence of Koplik spots (reddish spots
with a white centre) on the buccal mucosa. A characteristic
red rash appears on the third to seventh day beginning on the
face, becoming generalised and lasting 4 to 7 days.
- The frequency of complications varies in
different parts of the world. In industrialised countries, complications
occur in around 10-15 percent of cases and include diarrhoea,
otitis media, pneumonia, croup and typically, encephalitis.
In the developing countries at least three-quarters of cases
can be expected to have at least one complication and some have
multiple systems involvement. The case fatality rates in developing
countries are normally estimated to be 3-5 percent, but may
reach 10-30 percent in some situations. The three major causes
contributing to the high case-fatality rate are pneumonia, diarrhoea
- Measles can also lead to life-long disabilities,
including blindness, brain damage and deafness. Half of the
childhood corneal blindness in developing countries is attributable
to vitamin A deficiency, and half to measles infection. There
is no specific treatment of measles but case-fatality rates
can be reduced by effective case management, including the use
of vitamin A supplements. Immunization is the only way to prevent
Tetanus is caused by
naturally occurring bacteria that enter a body through open
wounds. Sometimes called "lockjaw," it is caused by a toxin
produced by bacteria called Clostridium tetani, which
is found in soil, stool and manure, and on anything lying
on the ground. It causes a generalized increased rigidity
of skeletal muscles, causing spasms, stiffness and arching
of the spine. Ultimately breathing becomes more difficult,
spasms occur more frequently, and in 70 to 100 percent of
the cases, mothers and infants will die.
- Neonatal tetanus (NT) - which affects newborn
babies - generally occurs during the first few days of life
and when a woman delivers her baby in unsanitary conditions,
often when a delivery occurs at home with no skilled birth attendant
- In the absence of immunization, transmission
occurs when bacteria comes in contact with broken skin, such
as that resulting from umbilical wounds and circumcisions. Poverty,
poor hygiene, and limited access to health services amplify
the risk for disease transmission during childbirth.
- Neonatal tetanus is the second leading
cause of death from vaccine-preventable diseases among children
worldwide. Maternal tetanus - affecting the mother - also occurs
as a result of poor hygienic practice at the time of delivery
or through gynecological complications. Immunizing women of
child-bearing age and women who are pregnant is an effective
method for preventing both neo-natal and maternal tetanus.
Tuberculosis (TB) is
a disease caused by Mycobacterium tuberculosis. The
initial infection may go unnoticed and remain latent/dormant
without symptoms but others may still be infected. Every
second, someone in the world is newly infected with TB,
and 1.5 million die annually from the disease.
- Although the disease is most common in
adults, it is usually more serious in infants, children and
adolescents. The disease can be reactivated after years of dormancy,
and is spread by prolonged close contact with an infected individual
through airborne droplets from a cough or sneeze by someone
who is infected with the organism.
- BCG vaccine (Bacillus Calmette-Guerin)
was developed in 1921. Early immunization is only effective
in preventing the most dangerous forms of TB (miliary forms
and meningitis) which occurs primarily in children. The vaccine
is given at or soon after birth, and coverage is the highest
of all the Expanded Programme on Immunization (EPI) vaccines
- over 85 percent globally. It has also been shown that the
vaccine provides cross-protection against leprosy.
Type b (Hib)
type b (Hib) is a bacterium that can colonise the human
nasopharynx. It is spread by droplets through coughs or
sneezing and is often exacerbated in overcrowded living
conditions. It is a leading cause of pneumonia and meningitis,
mostly in young children.
- Pneumonia is the most common manifestation
of Hib in developing countries, with an estimated 3 million
cases annually. The most serious manifestation of Hib is meningitis,
with a case-fatality rate of 3 percent to 5 percent in industrialized
nations, and up to 30 percent in developing countries. Meningitis
is marked by permanent neurological defects in 20 percent to
35 percent of survivors.
- Children less than 1 year of age are at
highest risk of the disease, while the disease is rarely seen
in children more than 5 years old. The failure to breast-feed,
household crowding, and day-care attendance are risk factors
for infection. Rapid diagnosis and treatment with antibiotics
are essential for optimal outcome in meningitis. Immunization
is one of the most cost-effective measures against this disease.
Hepatitis B virus is
spread from infected mothers to their infants at birth,
between young children, through contaminated blood and unsafe
injections and sex. Hepatitis B is the most serious type
of viral hepatitis and is also the only type causing chronic
disease for which a vaccine is available.
- Although most people are infected in infancy
or childhood, most deaths from hepatitis B occur in adulthood,
as a result of cirrhosis and/or liver cancer, both of which
are strongly associated with the virus. Hepatitis means inflammation
of the liver, and symptoms include yellowing of the skin and
eyes (jaundice), dark urine, extreme fatigue, nausea and vomiting,
and abdominal pain.
- An estimated 350 million people are chronic
carriers of the virus. In the developing world (sub-Saharan
Africa, most of Asia, and the Pacific) 8 percent to 15 percent
of people in the general population become chronic carriers.
Infection is less common in Western Europe and North America,
where less than 1 percent are chronic carriers. Immunization
is the only effective method to prevent the disease in infants.
Yellow fever is an acute
infectious disease that is caused by the yellow fever virus.
Humans may acquire the infection through the bite of an
infected mosquito. The "yellow" in the name is explained
by the jaundice that affects some patients.
- Yellow fever is now a serious public health
threat again. It has caused large epidemics in Africa and the
Americas. The WHO estimates that there are some 200,000 cases
of the disease and 30,000 deaths each year. Immunization is
the most effective method to prevent the disease.
- An outbreak of yellow
fever can go undetected because the signs and symptoms of yellow
fever are similar to viral hepatitis, malaria, Ebola/haemorrhagic
fever and other viral haemorrhagic fevers.
- In urban yellow fever, large epidemics
can occur when migrants introduce the virus into areas with
high human population density. Aedes aegypti mosquitoes
carry the virus from person to person. These outbreaks tend
to spread outwards from one source to cover a wide area.
- Symptoms of the disease do not appear until
3 to 6 days after infection. After this "incubation" period,
the infected person usually enters an "acute" phase that is
characterized by fever, muscle pain (with prominent backache),
headache, shivers, loss of appetite, nausea and/or vomiting.
Most patients improve and their symptoms disappear within three
to four days in this acute period, however, 15 percent enter
a "toxic phase" within 24 hours with fever, jaundice, abdominal
pains and vomiting. Half of the patients in the toxic phase
die within 10 to14 days. The remainder will recover without
significant organ damage.
Source: World Health Organization
GAVI Secretariat, c/o UNICEF,
Palais des Nations, 1211 Geneva 10, Switzerland
Tel: 41 22 909 5019 Fax: 41 22 909 5931 Email: Gavi@unicef.org