When two or more vaccines are mixed together in the same formulation , they can interfere as in live attenuated vaccines , where one of the vaccine components is more robust than the others and suppresses the growth and immune response to the other components . When two or more vaccines are mixed together in the same formulation , the two vaccines can interfere . This most frequently occurs with live attenuated vaccines , where one of the vaccine components is more robust than the others and suppresses the growth and immune response to the other components .