[Immunization against varicella and zoster]

Abstract

Two vaccines against varicella-zoster virus are available in France. These live attenuated vaccines are derived from the Oka strain used in Japan since 1974. They are indicated for healthy subjects from 12 months of age, at a dose of one injection until 12 years of age, and two injections 4-8 weeks apart for older children and adults. Seroconversion occurs in 95% of cases and the antibodies persist beyond 5 years. Clinical efficacy is about 85% against all forms of varicella and nearly 100% against severe forms. Post-exposure vaccination within 3 days may also prevent the disease. A universal immunization program against varicella was implemented in the USA in 1995. Now, with vaccine coverage at about 80%, the incidence of the disease has been reduced by 85%, with the largest decrease in 1- to 4-year-olds. Tolerability is generally good, with only mild reactions at the injection site and moderate fever The length of protection is not yet known. A two-dose schedule seems advisable to avoid breakthrough varicella, which occurs in 4% of vaccinees each year. Insufficient coverage is expected to lead to later disease onset, with more severe cases in adolescents and adults. Universal immunization could also increase the incidence of zoster. These problems indeed seem to be emerging in the United States. France has adopted restrictive guidelines on VZV vaccination, but they are expected to be revised when the combined MMR-V vaccine becomes available. Zoster vaccine, prepared with the same strain but at a higher concentration, has moderate efficacy on zoster and on post-zoster neuralgia in patients over 70. This vaccine is not yet recommended in France, because the length of protection is not known and there is a potential risk of delaying the occurrence of zoster and, thus, of increasing the risk of post zoster neuralgia.