"...The remarkable success of many vaccines, especially those administered in childhood, and their impressive safety record, together with the eradication of smallpox, are regarded among the greatest public health achievements of the 20th century..."

"...Records kept by the Centers for Disease Control and Prevention (CDC) since 1912 reveal the number of reported cases of an infectious disease before and after a vaccine became available.The decrease is remarkable: 100 percent in the case of indigenous poliomyelitis (the last case in the Americas was in Peru in 1992); over 99 percent in the case of diphtheria, measles, mumps, and rubella; and over 97 percent in the case of whooping cough (caused by Bordetella pertussis). All these agents undergo little antigenic variation (or drift) or none at all, showing that under virtually ideal conditions, vaccination can be extraordinarily effective...."

"...Within one year after the introduction in 1999 of a Neisseria meningitidis serogroup C conjugate vaccine in the United Kingdom, the incidence of meningitis was reduced by 92 percent among young children and by 95 percent among teenagers. A Salmonella typhi Vi conjugate vaccine (Vi-rEPA) reduced the incidence of typhoid fever among two-to-four-year-old children by more than 90 percent. Both findings confirm the remarkable effectiveness of conjugate vaccines..."

"...The experience with measles in the United States is of interest. From 1912 until 1963, the incidence never dropped below 100,000 cases per year, and epidemics were common. After the introduction of the first vaccine in 1963, the number of cases fell to very low levels and remained so until 1990, when there was an epidemic lasting three years and involving nearly 28,000 patients, most of whom were adolescents or young adults. This resurgence was due to inadequate vaccination of these patients at the age of one to two years in major urban areas. The recognition that immunity can wane after vaccination led to a two-dose vaccination schedule, which prevented the transmission of indigenous measles infections within the United States, Canada, and Finland..."

"...Sometimes, vaccination can fail, indicating that it induced a suboptimal immune response. The failure to respond or a low level of response to a simple vaccine, such as the hepatitis B vaccine, can be circumvented by adding additional helper-T-cell epitopes to the vaccine. In the case of varicella–zoster virus, like other such viruses, which induce latent infections, a live attenuated vaccine may not eliminate infection but does prevent chickenpox..."

"...In the United Kingdom in the 1970s, fears that the whole-cell pertussis vaccine induced brain damage caused vaccination levels to drop to approximately 30 percent. Two subsequent outbreaks of whooping cough caused more than 30 deaths, and many of the infected children suffered brain damage.A subsequent review of the evidence failed to substantiate the association between the vaccine and brain damage..."