The United States recommends immunisation against varicella for children. Should Europe?
Universal immunisation against varicella of children aged 12 to 18 months is recommended in the US but only 20% of 2 year olds have been vaccinated, according to an editorial (1) accompanying two papers on varicella in last week’s JAMA (2,3). A live attenuated vaccine against varicella - the virus that causes chickenpox and shingles (herpes zoster) - became available in the United States (US) two years ago, but is not licensed for universal use in Europe.
One of the papers (2) examined the effectiveness of varicella vaccine in an outbreak of chickenpox that arose in a day care centre for children aged under 6 years. Of 148 children with no history of varicella, 81 (55%) developed disease. Among 66 children who had received the vaccine, 9 (14%) developed varicella compared with 72 (88%) of the 82 unvaccinated children (vaccine efficacy was 86% overall, and 100% against moderate/severe disease). Cases who had been vaccinated had milder disease and were absent from the centre for fewer days than unvaccinated cases. The results provide reassurance about the vaccine’s stability: it must be stored in a frost-free freezer at -15°C or less and used within 30 minutes of reconstitution (2).
None of the children had received varicella vaccine more than 18 months earlier (2), so this study provided no data on the duration of immunity, but other data indicate that it may last for at least 20 years (1). A major concern about switching reliance from immunity acquired through natural infection to immunity acquired through immunisation is that, as immunisation reduces the incidence of the infection, people become less likely to have natural boosts to their immunity through subsequent exposures to infected people. Increasing numbers of adults - in whom the disease is often more severe, and in whom (currently) 55% of varicella deaths occur - might become susceptible to varicella. On the other hand, some evidence suggests that vaccinees may be less likely to develop herpes zoster than people who had varicella (1).
The editorial concludes that the evidence about the benefits of immunisation against varicella is sufficient to urge doctors (certainly in the US) to "just do it!". The situation in Europe is somewhat different. Austria, France, Germany, Greece, Italy, Luxembourg, Portugal and Switzerland have licensed varicella vaccine for use in high risk groups and their contacts only. One thing seems clear: if universal childhood immunisation were to be introduced coverage would have to be high, aiming to eliminate circulating infection. Other strategies might be considered - immunisation of children with impaired immunity (4) or healthy adolescents with no history of chickenpox (3), or of health care workers (4).