How many strains of chickenpox are there?

Chickenpox is caused by the varicella-zoster virus (VZV). There are three known strains of VZV:

* Wild-type VZV: This is the most common strain of VZV and is responsible for most cases of chickenpox.

* Vaccine-type VZV: This is a weakened strain of VZV that is used in the chickenpox vaccine.

* Oka strain: This is a highly attenuated strain of VZV that is used in some chickenpox vaccines.