Answer:
Because of Mutation
Explanation:
Every individual has a different genetic makeup. Most of the individuals have traits that protect them from certain diseases. The resistance to HIV is seen in approximately 1% of the individuals. The resistance is the result of changes in the factors that contribute to the attachment of HIV to the cell.
An HIV virus needs a chemokine co-receptor CC5, for the entry in the cell. In some individuals, a mutation of CC5 is present and is known as CCR5-Δ32 . This mutation doesn't allow the virus to enter the cell because it cannot attach itself to this receptor.
So, some individuals are not affected by HIV because of the mutation.
