THE PRESENT study is the fifth of the several pertussis immunization series in Grand Rapids during the past dozen years. In series I, reported in 1939,1 protection was demonstrated following pertussis vaccination; in series II and III, reported in 1943,2 protection was shown to follow immunization with an alum-precipitated vaccine and also with an alum-precipitated combined diphtheria toxoid and pertussis vaccine. In series IV, further observations are being made on the alum-precipitated combined antigen, and in series VI a combination fluid diphtheria toxoid and pertussis vaccine is being studied.
In series V the main objective was to study the effect of a reenforcing, or "booster," injection of pertussis vaccine on kindergartners who had received their original course of immunization at the city immunization clinics and for whom therefore we had definite records. Another objective was the tabulation of histories on all the children entering kindergarten, with respect to