Investigation of the response to the enterobacterial common antigen after typhoid vaccination.

A ntibodies against the Salmonella typhi enterobacterial com m on antigen (E C A ) an d the O and H antigens were investigated in sera from healthy m ale subjects who had been previously vaccinated with the typhoid vaccine. N o serological response to E C A was observed. Sera from subjects not previously vaccinated presented titers o f ECA hemagglutinins which quantitatively were related to the presence o fH titers, but not to O agglutinins but with no sta tistica l significance. The results are discussed in relation to the p oss ib le protective im m unological m echanism s in typhoid fever.