++
The human α-herpesvirus, varicella-zoster virus (VZV),
is a highly successful pathogen that has coevolved with its human
hosts over millennia. The majority of the world’s population
has experienced primary VZV infection as varicella (“chickenpox”),
with the acquisition of both lifelong immunity against reinfection
and the risk of viral reactivation as zoster (“shingles”).
In most children, chickenpox is a mild illness in which viral replication
rapidly subsides. However, severe and complicated varicella does
occur in previously healthy children and at much higher rates in
certain risk groups (eg, immunocompromised persons, adults, newborns). The
medical importance of VZV also extends to reactivation disease,
which poses a major societal burden of morbidity in the form of
postherpetic neuralgia, particularly in elderly individuals. A successful
vaccination program against varicella is having profound effects
on the epidemiology of VZV in the United States.
++
Varicella is acquired through close contact with an infected
individual. Natural varicella is the most communicable form of varicella-zoster
virus (VZV) disease: household attack rates approach 90%,
and outbreaks occur readily within groups of susceptible children.1 A
milder form of varicella, occurring in vaccinated individuals with partial
immunity, is only one third as transmissible,2 whereas
zoster represents the least contagious form of disease.
++
In unvaccinated populations in temperate climates, seasonal peaks of
varicella occur in the spring. These epidemics occur on a background
of endemic disease, and 84% of children acquire infection by
age 15 years.3,4 In contrast, the incidence of
varicella in the tropics does not vary by season and tends to be
delayed until adolescence or adult life.3 At this
age, morbidity and mortality from varicella are significantly greater
than in childhood, for reasons that are poorly understood.
++
Aside from adult age, the greatest risks for severe/fatal
varicella are cellular immunocompromise (congenital or acquired),
infancy (particularly, the neonatal period), and pregnancy (Table 314-1). In the prevaccine era, varicella was
associated with approximately 11,000 hospitalizations and in excess
of 100 deaths annually in the United States.5,6 Much
of this burden was borne by previously healthy children. The epidemiology
of VZV has been transformed since the introduction of universal
varicella vaccination in the mid-1990s. The incidence of varicella
has been strikingly reduced across all age groups, with concomitant
reductions in office visits, hospitalizations, and deaths from varicella.7-10
++