Varicella zoster virus infection: not always benign...but preventable

Varicella-Zoster virus (VZV) is a Herpesvirus responsible for both varicella or chickenpox, a common and highly contagious childhood infectious disease and zoster or shingles, a clinical manifestation of the viral reactivation, whose frequency increases with age. VZV infection is generally and wrongly regarded as a benign childhood disease: although it remains mild in the vast majority of cases, it can be associated with complications such as secondary skin bacterial infection, pneumonia, central nervous system dysfunction or Reye’s syndrome, and can even be occasionally fatal. The seriousness of VZV infection and its impact on health economic issues is becoming clearer as epidemiologic and pharmacoeconomic data become available.
However, varicella is a vaccine preventable infectious disease since a live attenuated varicella vaccine based on the Oka Japanese VZV strain vaccine has been developed in the 1970s. The most widely used vaccine are Varilrix (GlaxoSmithKine) and Varivax (Merck & Co).
A routine varicella vaccination programme targeting all healthy individuals over 1 year of age has been initiated in the US in 1995 and more recently in Canada and Australia. Vaccination is also recommended for susceptible healthy individuals at high risk if exposure. After a 10 years US experience, the vaccines have been shown to have a very good safety profile, to be well-tolerated and highly immunogenic and to provide around 85% protection against illness. When contracted after vaccination, what happens in a low percentage or cases, the disease remains mild and referred to as breakthrough. Immunity appears to assure a long-term protection.
Although such a universal childhood vaccination as well as a vaccination of adults and adolescents without history of chickenpox is recommended by the WHO, Europe appears to be more reluctant to varicella vaccination. Due to health policies that are different from one European country to another, the situation is not yet uniform. Although varicella vaccine is actually licensed and recommended for high risk patients in most European countries, it has been included in a routine immunisation schedule solely in Germany in July 2004 and more recently in Sicily.
The reluctance to the introduction of varicella vaccination is certainly due to the concern that low levels of coverage could increase the risk of delayed and thus more severe disease. The likelihood of achieving a high coverage rate, that could lead to a herd immunity and therefore avoid the problem of age-shift should be improved with a tetravalent vaccine which combine the existing measles-mums-rubella (MMR) vaccine for which high coverage levels are usually achieved with the varicella vaccine.
Such a combined approach has already been approved by the FDA and has received a positive opinion at the European Medicines Agency. It will certainly help to implement, in the near future, the universal varicella vaccination.