Vaccine-Preventable Disease Definitions

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NOTE: All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions.

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Chickenpox (Varicella)

Varicella is a highly contagious disease. Symptoms of the disease include fever, general feeling of illness and a rash of blister-like bumps. The virus is transmitted from person to person primarily by direct contact with infected persons, or from airborne spread of respiratory secretions. Although considered a common childhood disease, the varicella zoster virus can reactivate later in life and cause a painful sensory-nerve rash called shingles. Approximately 100 deaths per year nationally occur from complications of varicella.


Diphtheria is an acute infectious disease of the nose, throat, respiratory passages or skin caused by bacteria usually passed, via coughing or sneezing, from one infected person to the nose or throat of another. Symptoms include the gradual onset of a sore throat, a low-grade fever, and weakness. A thick mucus membrane often covers the entire throat and extends to respiratory passages, making it difficult to breathe. The lymph nodes of the neck tend to be enlarged. Diphtheria can lead to heart failure, paralysis and death.

Haemophilus influenza type b (Hib)

Hib bacteria reside in the nose and throat of many people without making them ill, but can cause serious illness, especially in preschool-aged children. Before a vaccine was available, Hib disease was the most common cause of meningitis in children under the age of five, and often led to pneumonia, skin infections, hearing loss, permanent brain injury or death. The disease is spread through the air by coughing and sneezing. Symptoms of illness include a high fever, severe headache, stiff neck, quiet or withdrawn behavior, sensitivity to light, vomiting, ear infections and convulsions. Hib infection can also cause epiglottitis -- a swelling in the throat which is potentially life-threatening.

Hepatitis A

Hepatitis A is an infection of the liver caused by the hepatitis A virus. It is spread from person to person by putting something in the mouth that has been contaminated with the stool of an infected person. Symptoms include lack of energy, diarrhea, fever, nausea and jaundice (yellow color to the whites of the eyes or skin). Not all infected people have symptoms but can still infect others. Many children do not have symptoms, so they often play a major role in passing the infection to others. The highest rates of hepatitis A are among children and young adults. Long term effects are uncommon, however there are about 100 deaths nationally each year from hepatitis A complications.

Hepatitis B

Hepatitis B is a potentially serious infection of the liver that can cause chronic liver disease and can lead to liver cancer. Symptoms include nausea, vomiting, abdominal pain and jaundice. However, many people who become infected have no symptoms. A small number of people infected with hepatitis B will carry the virus for life and can unknowingly spread the disease to others. The younger a person is when becoming infected, the greater the risk of chronic infection, chronic liver disease and liver cancer. The disease is spread through exposure to infected blood and body fluids. Hepatitis B can be spread by sharing toothbrushes, needles or razors that belong to an infected person; through contact with infected blood such as health care workers at a health care setting; using equipment that has not been sterilized for body-piercing or tattooing; having sex with a person who has hepatitis B; or by an infected mother to her baby during childbirth. A baby born to a mother who has hepatitis B has a 90 percent chance of getting the disease. Those babies infected have a 90 percent chance of becoming chronically infected and 25 percent will die of chronic liver disease as adults. Immunization at birth is important for prevention of the disease.

Human Papillomavirus (HPV)

Genital human papillomavirus (HPV) is the most common sexually transmitted virus in the United States. There are about 40 types of HPV. About 20 million people in the U.S. are infected, and about 6.2 million more get infected each year. HPV is spread through sexual contact. Most HPV infections don’t cause any symptoms, and go away on their own.  But HPV is important mainly because it can cause cervical cancer in women. Every year in the U.S. about 10,000 women get cervical cancer and 3,700 die from it. It is the 2nd leading cause of cancer deaths among women around the world. HPV is also associated with several less common types of cancer in both men and women. It can also cause genital warts and warts in the upper respiratory tract. More than 50 percent of sexually active men and women are infected with HPV at sometime in their lives. There is no treatment for HPV infection, but the conditions it causes can be treated. Protection from HPV vaccine is expected to be long-lasting. But vaccinated women still need cervical cancer screening because the vaccine does not protect against all HPV types that cause cervical cancer.

Influenza (Flu)

Influenza is a contagious respiratory illness caused by influenza viruses. The flu virus infects the nose, throat, and lungs and can cause mild to severe illness, depending on the individual. Older people, young children, and people with certain health conditions are at high risk for more severe flu complications. Some complications include bacterial pneumonia, ear infections, sinus infections, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. Hospitalization or death can result when these serious outcomes occur.

Meningococcal Disease (Bacterial Meningitis)

Meningococcal disease refers to any illness that is caused by a type of bacteria called Neisseria meningitidis, also known as meningococcus. Meningococcal disease is spread through respiratory and throat secretions (saliva and spit). The illness caused by these bacteria that most people are familiar with is meningococcal meningitis, which is often just called meningitis. Meningitis is an infection of the lining of the brain and spinal cord. These bacteria can also cause other severe illnesses, like bloodstream infections (bacteremia or septicemia). Meningococcal meningitis and meningococcal septicemia can both be fatal, and, in some cases, death can occur in just a few hours. Long-term effects of serious non-fatal cases can include hearing loss, brain damage, and amputation of toes, fingers, and limbs.


Measles is a potentially serious and highly contagious childhood disease. It can lead to ear infection, pneumonia, seizures, brain damage and death. Before the measles vaccine was introduced, measles caused about 400 deaths in the U.S. each year. Measles begins with cold-like symptoms-fever, red runny eyes, cough, runny nose and tiredness. This lasts about three days. Then small white spots appear on the inside of the mouth and a rash begins, usually on the face. This red, raised rash spreads rapidly over the neck, upper arms and chest. Later it spreads over the back, abdomen, rest of the arms, thighs, legs and feet. The illness lasts 7 to 10 days.


Mumps is caused by a virus. It usually causes painful swelling of the glands that lie just above the back angle of the jaw, but other glands may be affected. It can cause fever, headache and mild respiratory symptoms. After puberty, mumps can cause swollen testes or ovaries. Rarely, mumps causes deafness. Mumps is transmitted through the air or by direct contact with the saliva of an infected person. Many people with a mumps virus infection may have only mild symptoms that may resemble a cold. Symptoms of mumps generally last from one week to 10 days.

Pneumococcal Disease

Pneumococcal disease is caused by the Streptococcus pneumoniae bacterium, which is also known as pneumococcus. These bacteria are spread person-to-person by direct contact with an infected person’s saliva or mucus. Occasionally, people can carry the bacteria in their nose and throat without showing symptoms of illness. Certain groups are at higher risk for pneumococcal disease including children younger than 2 years of age, adults older than 65 years of age, people with certain diseases or conditions, people with cochlear implants, people with cerebrospinal fluid leaks, and smokers. There are many types of illness caused by pneumococcus bacteria, some of which are life-threatening. Pneumococcus is one of the most common causes of severe pneumonia and can lead to other types of infections, such as ear infections, sinus infections, meningitis (infection of the lining of the brain and spinal cord), and blood stream infections (bacteremia).


The wild polio virus has been eliminated in North and South America but not elsewhere in the world, which means all children should continue to be immunized against it. Polio is a viral infection transmitted by fecal-oral contact. Milder cases may last only a few days, causing fever, sore throat, stomachache and headache. If the disease worsens, it can cause severe muscle pain, paralysis, breathing difficulty, and even death.

Rubella (German Measles)

Rubella is a relatively mild viral illness that may go undiagnosed because of its mild symptoms. Although it seldom poses a major risk to children, rubella does put unborn infants at considerable risk. Pregnant women who get rubella can miscarry or have babies with severe birth defects. The first symptoms of rubella are usually swollen, tender glands at the back of the neck and behind the ears, a mild fever and then a rash. The rash and a "flush" appear first on the face, then spread quickly to the trunk, upper arms and thighs. The rash then moves to the forearms, hands and feet. Teenagers and adults may have painful or swollen joints.


Rotavirus is a virus that causes gastroenteritis (inflammation of the stomach and intestines). It is most common in infants and young children and spreads easily among those groups, but adults and older children can also become infected. Transmission occurs when rotavirus is passed into the environment from the feces of an infected person and then reaches a susceptible person’s mouth. The rotavirus disease causes severe watery diarrhea, often with vomiting. These symptoms can last from 3 to 8 days. Additional symptoms include fever, abdominal pain, and loss of appetite. Dehydration (loss of body fluids) is often seen in babies and young children. Rotavirus is the leading cause of severe diarrhea in infants and young children worldwide. Additionally, it is responsible for more than a half a million deaths each year in children 5 years of age and younger internationally.

Tetanus (Lockjaw)

Tetanus is a severe, often fatal disease. The bacteria that cause tetanus are widely distributed in soil and are found in the waste of many animals. People who get tetanus suffer from stiffness and spasms of the muscles. The larynx (throat) can close causing breathing and eating difficulties, muscles spasms can cause fractures (breaks) of the spine and long bones. Approximately 30% of the people who get tetanus will die from the disease.

Whooping Cough (Pertussis)

Pertussis is a highly contagious bacterial respiratory infection spread by coughing or sneezing. It starts like a common cold, but within a few days coughs come in exhausting bursts, often followed by a "whooping" sound as the person breathes in. Long coughing spells make it difficult for a person to eat, drink or even breathe. Vomiting can also follow a long coughing spell. The disease is most serious in small infants. With older children and adults the disease can be quite mild or can cause several weeks of exhausting coughing. Whooping cough is transmitted through the air when an infected person coughs.