Inactivated Vaccine
The first effective polio vaccine was developed in 1952 by Jonas Salk at the University of Pittsburgh, but it would require years of testing. To encourage patience, Salk went on CBS radio to report a successful test on a small group of adults and children on March 26, 1953; two days later the results were published in JAMA.
The Salk vaccine, or inactivated poliovirus vaccine (IPV), is based on three wild, virulent reference strains, Mahoney (type 1 poliovirus), MEF-1 (type 2 poliovirus), and Saukett (type 3 poliovirus), grown in a type of monkey kidney tissue culture (Vero cell line), which are then inactivated with formalin. The injected Salk vaccine confers IgG-mediated immunity in the bloodstream, which prevents polio infection from progressing to viremia and protects the motor neurons, thus eliminating the risk of bulbar polio and post-polio syndrome.
Beginning February 23, 1954, the vaccine was tested at Arsenal Elementary School and the Watson Home for Children in Pittsburgh, Pennsylvania. Salk's vaccine was then used in a test called the Francis Field Trial, led by Thomas Francis; the largest medical experiment in history. The test began with some 4,000 children at Franklin Sherman Elementary School in McLean, Virginia, and would eventually involve 1.8 million children, in 44 states from Maine to California. By the conclusion of the study, roughly 440,000 received one or more injections of the vaccine, about 210,000 children received a placebo, consisting of harmless culture media, and 1.2 million children received no vaccination and served as a control group, who would then be observed to see if any contracted polio. The results of the field trial were announced April 12, 1955 (the tenth anniversary of the death of Franklin D. Roosevelt; see Franklin D. Roosevelt's paralytic illness). The Salk vaccine had been 60–70% effective against PV1 (poliovirus type 1), over 90% effective against PV2 and PV3, and 94% effective against the development of bulbar polio. Soon after Salk's vaccine was licensed in 1955 children's vaccination campaigns were launched. In the U.S, following a mass immunization campaign promoted by the March of Dimes, the annual number of polio cases fell from 35,000 in 1953 to 5,600 by 1957. By 1961 only 161 cases were recorded in the United States.
An enhanced-potency IPV was licensed in the United States in November 1987, and is currently the vaccine of choice in the United States. The first dose of polio vaccine is given shortly after birth, usually between 1–2 months of age, a second dose is given at 4 months of age. The timing of the third dose depends on the vaccine formulation but should be given between 6–18 months of age. A booster vaccination is given at 4 to 6 years of age, for a total of four doses at or before school entry. In some countries, a fifth vaccination is given during adolescence. Routine vaccination of adults (18 years of age and older) in developed countries is neither necessary nor recommended because most adults are already immune and have a very small risk of exposure to wild poliovirus in their home countries.
In 2002, a pentavalent (5-component) combination vaccine (called Pediarix) containing IPV was approved for use in the United States. The vaccine also contains combined diphtheria, tetanus, and acellular pertussis vaccines (DTaP) and a pediatric dose of hepatitis B vaccine. In the UK, IPV is combined with tetanus, diphtheria, pertussis and Haemophilus influenzae type b vaccines. When the current formulation of IPV is used, 90% or more of individuals develop protective antibody to all three serotypes of poliovirus after two doses of inactivated polio vaccine (IPV), and at least 99% are immune to poliovirus following three doses. The duration of immunity induced by IPV is not known with certainty, although a complete series is thought to provide protection for many years.
Read more about this topic: Polio Vaccine