Elderly people are advised to get influenza (flu) vaccinations every year. Each year, a different type of flu vaccine has to be made. This is because

Options

A. different viruses attack people of different ages, so each year as the population ages, a new vaccine must be produced
B. vaccines are unstable and cannot be stored for more than one year
C. the body learns to destroy the antibodies made against the vaccine, so a new type of vaccine is needed for each vaccination
D. flu viruses change their genetic constituents so rapidly that vaccines against them rapidly become obsolete.

Answer

D

Explanation

Flu virus makes small erros due to mutations when it copies its genetic code during reproduction, But it lacks the ability to repair those eros, because it is an RNA virus and RNA, unlike DNA, lacks a self-correcting mechanism. As a result, flu virus is not genetically stable. Every generation is slightly different, and those differences accumulate as time passes. This slow deviation is called antigenic drift, and it sis the reason why it is necessary to reformulate flue vaccines every year. Every flue season, the genetic make-up of the dominant strains from the prior year will have drifted, changing the surface structure of those strains just enough to dimissh, or even destroy, the effectivenss of the previous year's vaccine.