Chickenpox vaccines: new drugs. A favourable risk-benefit balance in some situations.

(1) Chickenpox is generally mild. Most severe cases of chickenpox occur in immunocompromised patients, adults, and pregnant women (and their foetuses). (2) Two live attenuated chickenpox vaccines derived from the same strain of varicella virus (Oka) are marketed in France, under the trade names Varilrix and Varivax. (3) They have not been adequately evaluated in immunocompromised children. (4) The impact of routine vaccination of women of child-bearing age on complications of chickenpox during pregnancy has not been studied. (5) Immunogenicity studies in several thousand immunocompetent children aged from 1 to 12 years show that the vaccine is almost always immunogenic after a single injection. Other comparative studies in adolescents and adults show that two injections are needed, at least two months apart. (6) A double-blind placebo-controlled trial including 513 immunocompetent children showed that Varilrix prevented 88% of cases of chickenpox after a median follow-up of 29 months, but no data on severe chickenpox were reported. A study that followed up 9202 children aged 1 to 12 years for more than 13 years showed that vaccination with Varivax failed to prevent chickenpox in 12.5% of cases and that 1.7% of these cases were severe. (7) Immunocompetent children vaccinated within three days after exposure to the virus are partially protected, according to one study of Varilrix (104 children) and two small studies of Varivax (10 and 42 children). There are no equivalent studies in adults. (8) Local adverse effects such as fever and rash are common in immunocompetent vaccinees. The rash is sometimes varicella-like and is due to infection by the vaccine strain. Pharmacovigilance studies of Varivax have shown no serious adverse effects. (9) Disseminated and/or persistent infection caused by the vaccine strain has been reported in immunocompromised patients. (10) Vaccination of immunocompetent subjects does not appear to result in a risk of chickenpox transmission to subsequent contacts. There seems to be no increase in the risk of herpes zoster in vaccinated children nor is there any firm evidence that chickenpox vaccination increases the incidence of herpes zoster in the general population. (11) Little information is available on vaccination during pregnancy. As a precaution, however, pregnant women should not be vaccinated. (12) Mass vaccination does not appear to be justified: chickenpox is generally mild during childhood, and several questions concerning the effects of the vaccine remain unanswered. (13) Chickenpox vaccination should be restricted to specific groups of non immune immunocompetent adults who are in a position to transmit chickenpox to immunodeficient contacts (e.g. health care personnel and kindergarten staff); adults who have been in contact with a case of chickenpox within the past three days; and children awaiting transplantation. The potential benefits and risks of vaccinating immunocompromised patients should be assessed on a case by case basis.