Mutation is referred to as certain heritable changes in the genetic material (genome).
Viruses infect the host cell. However, after some time the host cell gains resistance towards the viruses. Hence, in order to overcome this and to multiply viruses mutate. Mutation is caused as a result of faulty coding of genes.
RNA viruses such as Influenza virus the virus keeps on mutating. Hence, individuals are often prone to
‘Common Cold’ caused by the Influenza virus. Since, the virus mutates and changes its form every time there is no definite vaccine or drug available against common cold.
Same is the case with the HIV virus.