Secondary and apparent primary antibody responses after group A streptococcal vaccination of 21 children.

A partially purified M protein, extracted from a mouse-virulent strain of type 3, group A streptococcus, was administered subcutaneously in gradually increasing amounts at weekly intervals to 21 children in a Family Program. Seven children with type 3 bactericidal antibody in prevaccination sera showed a secondary response. Of 14 children with no detectable type 3 bactericidal antibody prior to vaccination, 13 developed definite type 3 antibody during or soon after vaccination.