Passage: Salks vaccine was then used in a test called the Francis Field Trial, led by Thomas Francis, Jr., the largest medical experiment in history at that time. The test began with about 4,000 children at Franklin Sherman Elementary School in McLean, Virginia, and eventually involved 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 12 April 1955 (the tenth anniversary of the death of President Franklin D. Roosevelt, whose Franklin D. Roosevelts paralytic illness was generally believed to have been caused by polio). 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 Salks vaccine was licensed in 1955, childrens 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.
By how many polio cases did the prevalence decrease in the four years following 1953? Did more students receive a placebo or an actual vaccine? How many more children received the vaccine than those that received placebo? How many more percentage points of effectiveness was the Salk vaccine against PV2 and PV3 than against PV1 at best? How many percent more effective was the Salk vaccine at preventing bulbar polio than PV2? How many states chose not to particpate in the Salks vaccine? How many total children received the vaccine and the placebo? How many years did it take for there to be a drop from 35,000 cases of polio in a year to just 161? Was the Salk vaccine most effective against bulbar polio, PV2, or PV1? Was there a greater decrease in polio from 1953 to 1957, or 1957 to 1961?