Which vaccine strain is changed every yearly?: (A) Influenza, (B) Rabies, (C) Hepatitis, (D) Ebola
Answer is A. Influenza a and b are the segmented viruses which contain 8 segments of nucleic acid. There is gradual sequential change in antigenic structure occurring regularly at frequent intervals which is known as antigenic drift. This antigenic drift is due to mediation and selection so their vaccine strain is changed every year.