The Case for Live Poliovirus Vaccination **

Large scale programs for the control of poliomyelitis through the use of active immunization can be said to have started, both in the United States and elsewhere, in 1955. This step marked the end of a 40-year period in which experimental efforts to vaccinate against poliomyelitis had been repeatedly tried. As early as 1910, Dr. Simon Flexner, the Director of the Rockefeller Institute, and at that time the leading United States authority on the virus etiology of poliomyelitis, is quoted in a newspaper as having referred to Landsteiner and Popper's recent (1908) discovery of the virus of poliomyelitis' in the following terms: "Now that the virus of poliomyelitis has been discovered, the development of a vaccine to prevent the disease should only be a matter of months." There is no proof that Dr. Flexner ever made such a statement, but his contemporary colleagues do recall his eager hopes and it is unlikely that he (or they) suspected in 1910 that it would be a matter of some 540 months before such a prediction was to be realized in any true sense of the word, and, indeed, the search for an ideal vaccine may not yet be finished. The many interim, albeit sporadic, attempts to develop anti-poliomyelitis vaccines are fairly well known and started with experimental work in monkeys in which both killed and live virus vaccines were tried. The first of the trials in man were those with ricineolated and formalinized vaccines. They were not particularly successful. It was not until a few years after the composition of the poliovirus family, consisting as it does of three different serotypes, became knowne that Dr. Salk, working under the auspices of the National Foundation for Infantile Paralysis, began his work on a formalinized (killed) poliovirus vaccine. By 1954 the vaccine was ready for a large-scale field trial known today as the Francis field trial.' From that date forward, the control of poliomyelitis became a reality. Since 1955, therefore, the record has been impressive, and the prevalence of paralytic poliomyelitis has been appreciably reduced within areas where