What virus causes the flu? Why doesn't the body produce permanent immunity against that virus? How does the vaccine against the flu work?
Influenza virus types A, B, and C which is highly mutant DNA virus can cause the flu.
Due to the high mutation rate of the influenza virus which forms many different strains, the flu always presents epidemic features in affected populations and people may have several types of flu during their life. Therefore, the immune response was produced during previous infections will not be effective for future infections.
The vaccine against the flu is made of the attenuated virus of three different strains. The WHO (World Health Organization) investigates and determines every year which strains should compose the vaccine. This is the only strategy to combat the high mutation rate of the virus. By this way, the vaccine against the flu works.
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