In a previous survey of children who were given injections of diphtheria toxoid in the health centers of the Child Welfare Association of Montreal from 1926 to the end of 1934, it was found that there was a larger proportion of positive Schick reactions as the interval between the last dose of toxoid and the Schick test was prolonged.1 A further study was carried out to determine whether there was a progressive loss of immunity as the years following the administration of toxoid increased, as well as to determine the number of children whose reactions, after having previously been negative, reverted to positive.
Children who had received injections of diphtheria toxoid from one to ten years before and who were available were given Schick tests. Some who were inoculated earlier had two doses; all the others had three doses. No Schick tests were done on any of the children
BENJAMIN B, FLEMING G, ROSS MA. RESULTS OF SCHICK TEST IN CHILDREN ONE TO TEN YEARS AFTER INJECTIONS OF TOXOID. Am J Dis Child. 1940;60(6):1304-1312. doi:10.1001/archpedi.1940.02000060062006