Natural selection for rash-forming genotypes of the varicella-zoster vaccine virus detected within immunized human hosts

The Oka vaccine strain is a live attenuated virus that is routinely administered to children in the United States and Europe to prevent chickenpox. It is effective and safe but occasionally produces a rash. The vaccine virus has accumulated mutations during its attenuation, but the rashes are not explained by their reversion, unlike complications reported for other viral vaccines. Indeed, most of the novel mutations distinguishing the Oka...