Two variants or subtypes of HHV-6 are recognized based on DNA sequencing, cell tropism, and pathogenicity.
Subsequent infections are a result of reactivation.
Reactivation clearly occurs in the immunocompromised host. Reactivation may also occur in normal individuals. The epidemiology of HHV-6 infection differs with the variant. HHV-6B is endemic and is acquired early in childhood with rapid seroconversion after 6 months of age. Most children seroconvert by age 2.