Monitoring virus strain variation following infection with VZV: is there a need and what are the implications of introducing the Oka vaccine?

Varicella zoster virus (VZV) is a stable virus showing relatively little variation. Nevertheless, recent data have shown there to be at least four distinct viral strains. For the most part these are geographically segregated, but in areas of the world such as the UK, where mixed populations live, there is evidence for spread of all the genotypes. Little is known about the biological differences, if any, between these strains, yet recent data have shown that even a single nucleic acid change can affect the biological behaviour of the virus. The Oka vaccine has been licensed for mass vaccination in the US and for limited use in the UK, particularly in seronegative healthcare workers. Virological surveillance is needed to support these programmes and study the effect on virus spread. Evidence for VZV superinfection of latently infected individuals with different strains, and the increasing detection of VZV in association with clinical conditions such as viral meningitis, suggest more data are needed on the transmissibility and biological properties of the virus.