Question

Vaccination requirements vary from virus to virus. Some diseases require one vaccination that lasts for many years. Other diseases like the flu vaccine last a short time because the flu virus

A. Is less dangerous
B.is much smaller
C.mutates more rapidly
D.is more easily transmitted

Answer 1

C

Answer 2

"A vaccine works by training the immune system to recognize and combat pathogens, either viruses or bacteria. To do this, certain molecules from the pathogen must be introduced into the body to trigger an immune response.

These molecules are called antigens, and they are present on all viruses and bacteria. By injecting these antigens into the body, the immune system can safely learn to recognize them as hostile invaders, produce antibodies, and remember them for the future. If the bacteria or virus reappears, the immune system will recognize the antigens immediately and attack aggressively well before the pathogen can spread and cause sickness."

( http://www.publichealth.org/public-awareness/understanding-vaccines/vaccines-work/)

Viruses change (mutate) over time, and as a result the antigens can change too. If they change sufficiently, your body won't recognise them any more and so you will lose any immunity you gained from previous exposure to a vaccine or the real thing.