How many viruses are needed to cause infection?

The number of viruses needed to cause an infection can vary widely depending on the virus and the individual's immune response. For some viruses, a very low infectious dose—sometimes as few as one to ten viral particles—can initiate an infection. In contrast, other viruses may require a larger dose to overcome the host's defense mechanisms. Overall, the specific threshold for infection depends on factors such as the virus's virulence and the host's susceptibility.