Question

Each year, many people get a flu shot to protect themselves from the flu. Why give flu shots rather than "booster" injections? Why is last year’s flu shot ineffective against this year’s flu? As a class, discuss which of the following methods would be the best type of vaccination for fending off the flu, and explain your reasoning: A. IM (intramuscular) Injection B. Nasal Spray C. ID (intradermal) injection

Answer 1

Influenza viruses are constantly changing, they can change in two different ways: Antigenic drift and antigenic shift. The antigenic drift consists in small genetic changes, which accumulate over time and results in antigenically different viruses which can’t be recognized by the body’s immune system; the other type of change, the antigenic drift consists in a major genetic mutation which results in a new hemagglutinin or a new neuroaminidase (virus' proteins), or both new hemagglutinin and neuroaminidase and, these changes result ­­in a new influenza virus subtype that most people do not have immunity; hence, every year the flu vaccine has to be designed according to the specific viruses that are predicted that will be circulating. A booster injection is a re-exposure to the same immunizing antigen, in the case of influenza it would not work, because every year there’s a different type of influenza circulating.