Immunization

A combination vaccine against diphtheria, tetanus, and pertussis (DTP) was first licensed in the 1940s. The initial vaccine consisted of diphtheria and tetanus toxoids (a weakened form of the toxin that actually does the damage in the infections), and inactivated, whole pertussis bacteria. As seen in Table 2, tremendous reductions have been achieved in all three diseases. Use of the original whole-cell pertussis vaccine was marred in the past by concerns that the vaccine could cause brain injury (specifically, an encephalopathy). While this was largely disproven, the concerns were enough to lead many people to refuse the vaccine in the 1970s. In both Great Britain and Japan, the decline in immunization coverage resulted in epidemics of pertussis. In Great Britain alone, more than 100,000 cases of pertussis occurred between 1977 and 1979. In both countries, vaccination programs were restarted after the consequences of low immunization rates were seen. In the United States, a switch from the whole-cell pertussis vaccine to an acellular preparation with significantly less fever and local reactions was made in 1991.

The first polio vaccine was the injectable, inactivated polio vaccine (IPV) introduced in 1955. The live-attenuated oral polio vaccine (OPV) was licensed in 1960. Since the polio virus attacks the nerve cells that control muscle movement, vaccines against polio are responsible for enormous reductions in paralytic poliomyelitis throughout the world, and for the eradication of natural polio infection from the entire western hemisphere. In the United States, the OPV was used principally from the 1960s until 1997. Since 1997, a transition has been made to the IPV in order to eliminate any chance of vaccine-associated paralytic poliomyelitis caused by OPV. IPV has no risk of causing paralytic poliomyelitis. A complete switch to IPV occurred in the United States in January 2000.

The first live, attenuated measles vaccine was licensed in 1963, followed by mumps and rubella (German measles) vaccines in 1967 and 1969. The combined measles, mumps, and rubella (MMR) vaccine has been available since 1971. In the 1980s, epidemics of measles in the United States demonstrated the importance of immunizing and reimmunizing against measles. Concerns have been expressed over a possible link between autism and the measles vaccine, and this issue is discussed below under "Controversy over Vaccination."

The first hepatitis B vaccine was licensed in 1981. In the United States, an attempt at selective immunization of individuals (e.g., those having contact with blood or blood products, including health-care workers) with the hepatitis B vaccine did not control the number of new cases. Universal immunization of infants against hepatitis B with a vaccine began in 1990.

The Haemophilus influenzae type b (HIB) vaccine was first licensed in 1985. The initial vaccine could only be used in older children because it did not evoke protective immunity in younger infants. Unfortunately, most HIB disease occurs in the first two years of life. Subsequently, a new vaccine was introduced in 1990 that proved extremely effective in early infancy. By 1998, rates of serious bacterial infection due to HIB had declined by 99.7 percent since the introduction of the newer HIB vaccine in 1985.

A chicken pox (varicella) vaccine was licensed in 1995. Before the vaccine was available, an estimated four million cases of chicken pox infection occurred in the United States each year. While most cases of natural infection were uncomplicated, chicken pox was responsible for an estimated eleven thousand hospitalizations and one hundred deaths per year. Once the vaccine was available, chicken pox became the most common vaccine-preventable cause of death in the United States. Universal immunization with the chicken pox vaccine began the same year that the vaccine was licensed.

The pneumococcal-conjugate vaccine was licensed in 2000. Streptococcus pneumoniae (pneumococcus) is a leading cause of serious bacterial infection in childhood, including pneumonia, bacteremia (bacteria in the blood), and meningitis. Pneumococcus is also the most common cause of ear infections in children.