infection is caused by the hepatitis A virus (HAV).
In the United States, hepatitis A is
one of the most frequently reported diseases that can be prevented
by a vaccine. When infected by hepatitis A virus, adolescents and
adults are more likely than young children to develop signs and
symptoms of disease, including fever, weakness, nausea, abdominal
pain, dark urine, and yellow eyes and skin, and are more likely to
experience severe disease.
Symptoms usually last less than
two months, but 10% to 15% of those infected will have prolonged or
relapsing disease lasting up to six months. Unlike hepatitis B and
C, chronic hepatitis A disease does not occur. Unfortunately, each
year in the U.S. 125,000 to 200,000 people become sick with
hepatitis A, and 70 to 100 people die, mostly those with underlying
This virus is most commonly spread
in stool, although it can be spread through contact with infected
blood. Outbreaks sometimes occur when many people have eaten from
the same Hepatitis A-infected food source. Infected people are most
likely to spread hepatitis A virus during the two-week period before
they know they are infected. Since most infected pre-school children
show no symptoms of hepatitis A infection, they often unknowingly
spread the hepatitis A virus to others.
About one-third of the hepatitis A
cases in the U.S. occur in children 5 to 14 years of age. The lowest
rate of infection is in adults more than 40 years old. The rate of
infection is higher in lower income populations, and the disease is
more common in areas with higher populations of American Indian and
Alaskan natives than in other areas of the country.
Hepatitis B virus (HBV)
is transmitted from one person
to another through blood and body fluids, and primarily infects the
liver. In the United States, it is most commonly spread through
sexual contact or injection drug use. Health care workers and others
exposed to infected blood or body fluids are also at high risk for
infection. However, approximately 30% of those infected have no
known risk factors. Worldwide, it is most commonly spread to infants
by their infected mothers.
More than half of those infected with the disease show no signs or
symptoms, although they may become chronic carriers of the disease
and may develop liver disease or liver cancer later in life (usually
by age 40). Symptoms of HBV infection vary and may include loss of
appetite, fatigue, nausea, and jaundice (yellow eyes and skin),
joint pain, and skin rashes.
Worldwide, over 350 million people
have chronic HBV infection, and approximately 1 million HBV patients
die annually. An estimated 1.25 million people in the U.S. have
chronic HBV infection. Each year, approximately 4,000 to 5,000
children are infected with hepatitis B in the United States. The
younger the patient is when the disease is acquired, the more likely
it is that he or she will develop chronic liver disease or liver
Approximately 90% of infants who
are infected from their mothers at birth, and between 30 and 50% of
those infected before age five, become chronic HBV carriers, while
people who are newly infected as adults have only a 6 to 10% risk of
chronic infection. For these reasons, hepatitis B immunizations are
recommended for routine administration in early infancy.
C is not vaccine preventable at this time.
is caused by intestinal viruses that spread from person to person in
stool and saliva. Most people infected with polio (approximately 95%)
show no symptoms. Minor symptoms can include sore throat, low-grade
fever, nausea, and vomiting. Some infected persons (1 to 2%) will have
stiffness in the neck, back, or legs without paralysis. Less than 1% of
polio infections (about 1 of every 1,000 cases) cause paralysis. In some
cases, the poliovirus will paralyze the muscles used to breathe, leaving
the victim unable to breathe on his or her own. Many paralyzed persons
recover completely. Those who do recover from paralytic polio may be
affected 30 to 40 years later, with muscle pain and progressive
Before the polio vaccine, 13,000 to
20,000 people were paralyzed by polio, and about 1,000 people died from
it each year in the United States. Most of those infected were
elementary school children so it was often called 'infantile paralysis.'
The incidence of paralytic polio
peaked in the U.S. in 1952 with 21,000 reported cases and numerous
deaths. Following licensure of the Salk (inactivated) polio vaccine in
1955, the incidence of the disease fell dramatically. The disease was
further reduced by the advent of the Sabin (oral) polio vaccine in 1961.
The last cases of paralytic polio from natural poliovirus in the U.S.
were in 1979, and the most recent case from outside the U.S. occurred in
is caused by a virus that is transmitted
from person to person in mucus droplets coughed or sneezed into the
environment. Rubella usually is a mild illness. Symptoms include
low-grade fever and swollen lymph nodes in the back of the neck followed
by a generalized rash. Complications may include joint pain, a temporary
decrease in platelets, and encephalitis (inflammation of the brain).
Temporary arthritis may also occur, particularly in adolescents and
expectant women often leads to congenital rubella syndrome (CRS) in
their fetuses. This is a devastating disease characterized by deafness,
mental retardation, cataracts and other eye defects, heart defects, and
diseases of the liver and spleen that may result in a low platelet count
with bleeding under the skin. The incidence and severity of congenital
defects are greater if infection occurs during the first month of
gestation. Up to 85% of expectant mothers infected in the first
trimester will have a miscarriage or a baby with CRS.
The World Health Organization
estimated that, in 1999, 110,000 infants were born with CRS worldwide.
Although most CRS occurs in developing countries, it also continues to
occur in the U.S., mostly among unimmunized Hispanics.
Before a vaccine was available, there
was a rubella outbreak in the U.S. (1963 to 1964), during which 12
million people developed the disease. Because many of those infected
were expectant mothers, 11,000 fetuses died and 20,000 babies were born
with permanent disabilities as a result of exposure to the virus. The
number of cases of rubella fell very sharply once the rubella vaccine
was licensed in 1969; today there are fewer than 1,000 cases of rubella
reported each year in the U.S. on average and less than 10 cases of
congenital rubella syndrome.
is a bacterial infection caused by Bordetella pertussis. The
germ is spread when infected people cough or sneeze.
Children with pertussis
have decreased ability to cough up respiratory secretions and develop
thick, glue-like mucus in the windpipe. This causes severe coughing
spells that make it difficult for them to eat, drink, or breathe. The
child may suffer from coughing spells for two to three weeks or longer.
Sometimes the child coughs several times before breathing in; when the
child finally does breathe in there is often a loud gasp or "whooping"
sound. The disease is most severe when it occurs early in life; it often
The majority of
pertussis-related deaths are in young infants which may occur when other
bacteria take the opportunity to invade the sick infant's lungs. Primary
pertussis pneumonia also may be life-threatening in infancy. In 1997,
adolescents and adults accounted for 46% of reported cases of pertussis,
and they are often the ones who spread this disease to infants and
Pertussis is one of the
most contagious human diseases, so it is a great risk to those who are
unvaccinated. Pertussis will develop in 90% of unvaccinated children
living with someone with pertussis, and in 50% to 80% of unvaccinated
children who attend school or daycare with someone with pertussis.
Approximately 50 out of every 10,000 people who develop pertussis die
from the disease.
before widespread vaccination, as many as 175,000 cases of pertussis
were reported in the United States each year, with approximately 8,000
deaths caused by the disease. Today, there are about 7,000 cases of
pertussis and 10 deaths annually. Worldwide, there are an estimated
300,000 annual deaths due to pertussis.
(chickenpox) is an infection
caused by the varicella-zoster virus (VZV). The infection usually starts
as a rash on the face that spreads to the rest of the body. The rash
begins as red bumps that eventually become blisters. A child will often
get 300 to 500 blisters during the infection, which crust over and fall
off in one to two weeks. The virus can be spread in the fluid from the
blisters or droplets from an infected person’s nose or throat.
Varicella is generally a mild disease,
but it is highly contagious and can be severe and even fatal in
otherwise healthy children (less than 1 out of every 10,000 cases).
Chickenpox can cause pneumonia (23 out of every 10,000 cases), and is an
important risk factor for developing severe invasive “strep” (group A
streptococcal disease), commonly referred to as “flesh-eating disease.”
Treatment of this deep infection requires antibiotics and surgery to
remove the infected tissue. Complications of varicella include bacterial
infections, decreased platelets, arthritis, hepatitis, and brain
inflammation (1 in 10,000 cases), which may cause a failure of muscular
coordination. Complications are more common among adolescents and
adults, and in immunocompromised persons of all ages, than in children.
The virus which causes chickenpox
remains in the body for life and may reappear as shingles, particularly
in the elderly.
A women who contracts chickenpox in
early pregnancy can pass the virus to her fetus, causing abnormalities
in 2% of cases. The fetus can develop scarring of the skin and affected
limb(s), limb deformities (hypoplesia), eye damage, low birth weight,
brain atrophy, and mental retardation. The virus sometimes leads to
fetal demise or spontaneous abortion, while some infected fetuses die in
infancy. A pregnant woman who has never had chickenpox, but has been
exposed, should contact her physician immediately.
Prior to the approval of the vaccine,
there were 3 to 4 million cases of varicella in the United States each
year. About 10,000 people were hospitalized with complications, and
approximately 100 patients died. While only 5% of reported cases of
varicella are in adults, adults account for 35% of the deaths from the
is caused by toxin-producing spores that inhabit the soil and the bowels
of animals and humans. Unlike other vaccine-preventable diseases, it is
not spread from person to person. Tetanus infection is most often the
result of wound contamination in an unimmunized person. Tetanus may
occur following delivery in newborn babies of unimmunized women
(resulting from contamination of the umbilical cord), and in injection
drug users. It may also occur following puncture wounds, animal bites,
burns, abrasions and surgery.
Tetanus infection results in severe
muscle contractions, or spasms. Fever, sweating, elevated blood
pressure, and rapid heart rate may also occur. Spasms of the vocal cords
or the muscles of respiration can interfere with breathing, and
pneumonia is common. Contraction of muscles can be so severe that the
spine or other bones are fractured.
Between 40-60 cases of tetanus are
reported in the United States each year, and 30% of those infected with
tetanus in the US die. Death is more likely in newborn infants of
unimmunized mothers and patients over 50.
is a serious disease that can
cause death through airway obstruction, pneumonia, heart failure, and
paralysis of the muscles used for swallowing.
Diphtheria usually begins with a sore
throat, slight fever, and swollen neck. Most commonly, bacteria multiply
in the throat, where a grayish membrane forms. This membrane can choke
the person. Sometimes, the membrane forms in the nose, on the skin, or
other parts of the body. The bacteria can release a toxin that spreads
through the bloodstream and may cause muscle paralysis, heart and kidney
failure, and death. Approximately 5% of people who develop diphtheria
(500 out of every 10,000) die from the disease and many more suffer
In the 1920s, before the diphtheria
vaccine, there were 100,000 to 200,000 reported cases in the United
States each year. Because of the high level of immunization, only one
case of diphtheria was reported in the United States in 1999. However,
in areas where the immunization rate has fallen (such as Eastern Europe
and the newly independent states of the former Soviet Union), tens of
thousands of people suffered from diphtheria in recent years.
The diphtheria vaccine offers the
greatest protection against this disease. The fully immunized person who
is exposed can become a carrier of infection, may only develop a mild
case, or may not get sick at all. But if not fully vaccinated, the risk
of getting severely ill is 30 times higher.
affect anyone, and epidemics of influenza occur during the winter months
nearly every year. Influenza is spread through coughing and sneezing,
and is highly contagious, especially in childcare centers, schools, and
generally comes on suddenly, and symptoms include muscle aches, fever,
chills, headache, cough, and runny nose. Young infants may develop
croup. The most frequent complication of influenza is pneumonia.
Myocarditis (inflammation of the heart) and worsening of chronic lung
diseases also may occur.
On average, influenza causes
approximately 36,000 deaths and 148,000 hospitalizations each year in
the United States. More than 90% of influenza-related deaths are in
people aged 65 years or older.
is a serious disease caused by a highly contagious virus, which spreads
when people touch or breathe in infectious droplets passed by coughing
and sneezing. Measles begins with fever followed by cough, runny nose,
and conjunctivitis ("pink eye"). Infections of the middle ears,
pneumonia, croup, and diarrhea are common complications. Measles
encephalitis (an infection of the brain) occurs in 1 per 1,000 cases of
natural measles, frequently resulting in permanent brain damage in the
survivors. Approximately 5% of children (500 out of 10,000) with measles
will develop pneumonia. In addition, 1 to 3 of every 1,000 children who
get measles in the United States dies from the disease.
Death is more common in infants, in
malnourished children, and among immunocompromised persons, including
those with leukemia and HIV infection.
Prior to licensure of the first
measles vaccine in 1963, virtually every person in the U.S. got the
measles by age 20. Since the vaccine became available, there has been a
99% reduction in the incidence of measles. However, measles is still
being “imported” from other countries. The most recent outbreaks
occurred in the U.S. between 1989 and 1991, resulting in 755,000 cases
and 123 reported deaths.
Mumps is a
viral infection spread from person to person by secretions sneezed or
coughed from the nose or throat.
Mumps usually begins with swelling and
tenderness of one or more of the salivary glands. This lasts about a
week. Complications can include inflamed testicles (20% to 50% of
post-pubertal males infected), brain involvement including aseptic
meningitis (15% of cases), and inflammation of the pancreas (2% to 5% of
cases) and ovaries (5% of post-pubertal females). Permanent deafness
occurs in 1 out of 2,000 cases.
The mumps virus has not been
associated with problems during pregnancy, although there are some
reports of an increase in fetal loss associated associated with mumps
during the first trimester.
Before widespread vaccination, there
were about 200,000 cases of mumps and 20 to 30 deaths reported each year
in the United States. In 1998, there were just 600 cases of mumps and no
fatalities reported from the disease.