A large-scale field trial has been undertaken to test the effectiveness of a vaccine against poliomyelitis developed by Dr. Jonas Salk of the University of Pittsburgh. Nearly 500,000 children in the United States, Canada, and Finland have received vaccine injections — with an absolute minimum of untoward reactions. The vaccine is unquestionably safe.

The plan of study and evaluation set up for the field trial will permit exact answers to the questions: "To what extent does vaccination protect against paralytic poliomyelitis under natural conditions of exposure?" and "Exactly what kind of protection does the vaccine offer?"

It is possible that the vaccine will offer complete protection against paralytic poliomyelitis to a high percentage of vaccinated children. It is also possible that the vaccine, while not offering complete protection against paralysis, will nevertheless modify the course of the disease to the extent that residual paralysis will be greatly reduced.

The final evaluation of the vaccine and its use in the 1954 field trial is being made independently by the Poliomyelitis Vaccine Evaluation Center at the University of Michigan, under the direction of Dr. Thomas Francis. A report is expected in 1955, probably in the spring of the year. These evaluation studies will determine the future use of the vaccine.