The virus that causes mumps in humans is composed of a protein outer shell containing a core of dna. the virus that causes the flu in humans is composed of a protein outer shell containing a core of rna. vaccines that are effective against mumps work efficiently year after year. vaccines that work against the flu must be revised and changed every year. what accounts for the difference in the effectiveness of these two vaccines? a) rna based viruses are more efficient at infecting many people. b) dna mutates more rapidly than rna and so causes a more deadly virus. c) dna based viruses are more easily defeated by the human body since our own cells are made of dna. d) rna mutates more rapidly than dna causing change in the viruses, so vaccines have to be updated regularly.