Successes and remaining challenges after 10 years of varicella vaccination in the USA.

Beginning in 1995, universal varicella vaccination was recommended in the USA for all children aged 12-18 months, and all susceptible adolescents and adults. Many physicians were initially sceptical about the need to prevent primary varicella. However, with passage of state daycare and school entry mandates for varicella immunization, national varicella vaccination rates increased to approximately 90% by 2004. Several studies have demonstrated concomitant reductions in varicella-related healthcare utilization, costs and varicella-related mortality among children in the vaccinated age group, as well as adults. Remaining challenges include: first, outbreaks of 'breakthrough' varicella in vaccinated populations, which may prompt a second-dose recommendation, and second, possible increases in the incidence of secondary varicella (zoster) among adults whose natural immunity may wane in the absence of endemic varicella. The latter concern highlights the importance of a promising new varicella vaccine for older adults that may be licensed and recommended in the next 2 years.