Smallpox:  Varying strains of smallpox disease have been identified, each extremely infectious and leading to skin lesions, permanent scarring, and serious illness. Depending on the strain, fatality rates run as high as 25 percent to less than one percent.vii  Smallpox is immunization’s greatest success story to date, as this dreaded disease has been eradicated.  As of the early twentieth century, tens of thousands of smallpox cases were reported in the U.S. each year.viii  The last case of smallpox in the U.S. was reported in 1949, and routine vaccination of American children ended in 1971. The last case of smallpox in the world occurred in Somalia in 1977.ix  In 1980, scientists officially declared that vaccines had been successful at eradicating smallpox worldwide.

Polio:  Before polio vaccine was available, the U.S. had 50,000 polio cases a year, including 13,000 to 20,000 cases of paralytic polio. These annual epidemics of polio often left thousands of victims -- mostly children -- permanently in braces, crutches, wheelchairs, and with iron lungs.x  Immunization has eliminated the disease in the U.S. and Western Hemisphere, and the World Health Organization had set a goal of eradicating polio worldwide by the end of 2004.  However, Nigeria's northern State of Kano suspended polio immunization in August 2003 amid rumors that the vaccine was contaminated with HIV and that it caused infertility.  Consequently, polio cases reemerged in Nigeria and other previously polio-free countries. Polio immunization has restarted in Kano and the WHO now estimates that polio can be eradicated by the end of 2005.xi

Measles:  Measles is one of the most infectious diseases in the world; more than 90 percent of people who are not vaccinated will get measles if they are exposed to the virus.  In the U.S., roughly one in five who develop the disease require hospitalization for one or more complications.xii  Before 1963, more than three million cases of measles and 500 deaths from measles were reported each year. More than 90 percent of children had measles by age 15.xiii  Widespread introduction of vaccine has resulted in a reduction of measles incidence from 894,134 cases in 1941 to 89 cases in 1998 and 44 cases in 2002.xiv, xv

Pertussis:  Pertussis (also known as whooping cough) can be a severe illness, resulting in prolonged coughing spells that can last for many weeks or even months.  In children, the disease often leads to vomiting and can interfere with efforts to eat, drink, and breathe; children often suffer dehydration and lost weight, and infants are prone to pneumonia, brain damage, seizures, and mental retardation.xvi  Before pertussis immunization was available, nearly all children developed whooping cough.  The CDC reports that following the introduction of immunization in the mid-1940s, pertussis incidence declined more than 99 percent by 1970 and to an all-time low of 1,010 cases by 1976.  However, since then, an increase in incidence of the disease has been documented, with more than 10,000 cases reported in 2003 and outbreaks occurring every three to four years.  Furthermore, some researchers have estimated that only one-third of pertussis cases in the U.S. are actually reported. xvii

Diphtheria:  Diphtheria is a serious bacterial disease that frequently causes heart and nerve problems. The death rate is five percent to 10 percent, with higher death rates (up to 20 percent) in the very young and the elderly.  In the 1920s, prior to regular immunization, there were 100,000 to 200,000 American cases of diphtheria each year and 13,000 people died from the disease.xviii  Since the introduction of immunization, diphtheria has dramatically declined from a high of 206,939 reported cases in 1921 to one in 2002. xix, xx

Haemophilus Influenzae type B (Hib):  Before Hib vaccination, Haemophilus influenzae type B caused serious infections in 20,000 children each year, producing meningitis (12,000 cases) and pneumonia (7,500 cases), bacteria in the blood, and inflammation of the epiglottis.xxi  Hib meningitis killed 600 children each year, and left many survivors with deafness, seizures, or mental retardation.  Since introduction of conjugate Hib vaccine in December 1987, the incidence of Hib has declined by 98 percent. xxii    The number of cases of serious Hib disease in children under five years of age reported in 2002 was 331.xxii

Rubella:  While rubella is usually mild in children and adults, up to 90 percent of infants born to mothers infected with rubella during the first trimester of pregnancy will develop congenital rubella syndrome (CRS), resulting in heart defects, cataracts, mental retardation, and deafness. Expectant mothers are now routinely tested for rubella antibodies during pregnancy.  From 1964-1965, before routine rubella immunization, there was an epidemic of 12.5 million cases that resulted in an estimated 20,000 infants born with CRS; 2,100 neonatal deaths; and 11,250 miscarriages. Of the 20,000 infants born with CRS, 11,600 were deaf, 3,580 were blind, and 1,800 has mental retardation.  Due to the widespread use of rubella vaccine, only 18 cases of rubella and one case of CRS were reported in 2002.xxiv 

Hepatitis B:  National studies show that about 12.5 million Americans have been infected with hepatitis B virus at some point in their lifetime. Over 10 percent of these individuals develop chronic infection, increasing chances for chronic liver disease, cirrhosis, and liver cancer.  An estimated 20 to 30 percent of such cases stem from infection during childhood.  Approximately 5,000 people die each year from hepatitis B-related liver disease resulting from chronic hepatitis B.  However, with the recent advent of vaccine, the number of new infections per year has declined from an average of 450,000 in the 1980s to 7,996 in 2002.xxv  The greatest decline has occurred among children and adolescents due to routine hepatitis B vaccination.xxvi

Tetanus:  Tetanus, commonly known as Lockjaw, is a severe disease that causes stiffness and spasms of the muscles and is often fatal. The larynx (throat) can close causing breathing and eating difficulties, muscles spasms can cause fractures (breaks) of the spine and long bones.  Some people go into a coma, and die. Approximately 30 percent of reported cases end in death.  From 1922-1926, there were an estimated 1,314 cases of tetanus per year in the U.S.xxvii  In 2002, as a result of extensive immunization, only 25 cases of tetanus were reported.xxviii

Mumps:  While usually a mild disease, mumps can produce swelling of the brain, nerves and spinal cord which in some cases leads to paralysis, seizures, and fluid in the brain.  Moreover, in children, it is a major cause of deafness.  Prior to immunization, the U.S. suffered approximately 200,000 cases per year.  After vaccine licensure in 1967, reports of mumps decreased rapidly, but brief resurgences, such as an epidemic in 1987 that led to a reported 12,848 cases occurred.  Since then, a second dose of mumps vaccine was added to the standard childhood MMR series and as a result, annual cases are now in the hundreds rather than the thousands.xxix 

Varicella:  Although generally mild, varicella (chickenpox) virus can lead to severe illness causing complications such as secondary bacterial infections, severe loss of fluids (dehydration), pneumonia, central nervous system irregularities, and shingles.  The virus is highly contagious and thus virtually all unimmunized individuals contract varicella if exposed to the virus, usually prior to adulthood.  Before immunization, the U.S. reported an estimated four million cases a year, leading to approximately 11,000 hospitalizations and 100 deaths.  A new chickenpox vaccine was licensed in 1995, and incidence of the disease is now declining.xxx Chickenpox can be particularly dangerous to a developing fetus.  Pregnant women who have never had chickenpox are at risk of contracting chickenpox during pregnancy. A small percentage of women who get chickenpox in the first or second trimester can have babies with birth defects known as "congenital varicella syndrome." In addition, chickenpox may be more severe in pregnant women than in others putting the woman at risk of severe complications. Vaccinating close contacts of a susceptible pregnant woman is the most effective way to protect her from disease.xxxi

Influenza:  Influenza is a serious disease.  In an average year, the flu causes 36,000 deaths and 114,000 hospitalizations in the United States. While the majority of deaths resulting from flu occur in the elderly, rates of infection are highest among children and hospitalization rates among children zero-to-one year old are similar to those of the elderly.