To the Editor: Funding of universal varicella zoster vaccine (VZV) at ages 18 months and 10–13 years was recently announced in Australia. Health professionals should be aware of a number of related issues.

Varicella vaccination was recommended in the United States from 1996 for all children aged 12–18 months, with catch-up vaccination to age 13 years. US surveillance shows:

• Decreased varicella mortality in all age groups except those aged ≥ 50 years (average varicella deaths per year: 145 in 1990–1994 versus 66 in 1999–2001).1

• Decreased varicella cases in all age groups, with a non-significant reduction in hospitalisations (average annual hospitalisations in three surveillance regions: 40 before vaccination versus 14 after vaccination).2

US data on herpes zoster have not yet been published.

There are concerns that, in the longer term, universal varicella vaccination may increase the incidence of adult varicella and herpes zoster, similar to the effect of pertussis vaccination on adult pertussis. Modelling in the United Kingdom predicted that universal infant vaccination would initially reduce varicella, but would result in increases in herpes zoster 5–10 years later and adult varicella 20–40 years later.3 In contrast, modelling of adolescent vaccination predicted a small decrease in varicella, but no increase in later adult varicella.3

Varicella is generally perceived as a mild illness, while vaccination is largely valued for preventing serious, life-threatening conditions. Anecdotal reports of low levels of private purchase of VZV in Australia suggest it may not be a priority for some families. With 36% of general practitioners concerned about unknown side effects of VZV,4 and public concern about vaccine adverse events in the face of low disease rates, the level of acceptance of universal varicella vaccination by providers and consumers is uncertain.

Alternatives to universal varicella vaccination were a high-risk strategy (vaccination of children with chronic illness and family members of high-risk individuals) or waiting until US disease patterns were established. These were real options as:

• A high-risk strategy may prevent up to 45% of paediatric hospitalisations.5

• Hospitalisation and herpes zoster contribute more to health costs than treatment in the community or acute varicella.5

• Natural infection, at the cost of disease, immunises most of the population.

Any increase in adult varicella and herpes zoster caused by varicella vaccination may be alleviated by booster doses, but the added cost, difficulty in reaching the target population, and potential impact on community confidence in vaccination may be significant problems. The universal varicella vaccination program will test providers’ and consumers’ acceptance of vaccination against what is perceived as a mild illness.

Comment: Recently published data have added considerably to the evidence about the impact of varicella vaccination programs, and address many of the concerns raised by Mackenzie.

First, in the United States where universal varicella vaccination was recommended a decade ago, recent data show that — despite much slower implementation than is expected in Australia — varicella-related disease has declined by up to 90%, and hospitalisation rates and deaths from varicella by more than two-thirds, due to herd immunity.1,2

Second, data have now been published on the incidence of herpes zoster in areas of sentinel surveillance in the US, showing no change in age-specific rates to 2002.3 Along with the success of a recent trial of high-dose varicella vaccine in reducing herpes zoster in older adults,4 these data add to confidence that any increase in herpes zoster — as predicted in some models — will be detected and effectively combated by vaccinating people aged over 60 years. A substantial allowance for surveillance of both varicella and herpes zoster was included in the 2005 federal budget, to accompany the introduction of universal varicella vaccination in Australia.

Mackenzie is correct that varicella is perceived by some as a mild illness, but it is important for general practitioners to emphasise to patients that this is incorrect.5 Each year in Australia, varicella causes around seven to eight deaths and more than 1500 hospitalisations,6 many associated with serious complications, such as invasive bacterial infection, pneumonia, and encephalitis. Although complications are more likely in adults and immunocompromised patients, 42% of hospitalisations are in children aged 0–4 years,6 most of whom are otherwise healthy.7

Patients can also be reassured about the safety of varicella vaccines, as clinical trials now date back 30 years, and more than 40 million doses of vaccine have been distributed in the US.

Mackenzie suggests alternatives to universal childhood varicella vaccination, such as vaccination of “high risk” patients and their families, or of adolescents alone. However, these programs would not prevent morbidity among otherwise healthy young children and older age groups, as they would be insufficient to generate herd immunity. Moreover, age-based vaccination strategies have been shown to be easier to implement than more targeted programs. In the absence of a publicly funded universal program, the private market could sustain modest varicella vaccination rates of around 40%–50% in Australia.8 This would increase the number of adolescents and adults susceptible to varicella, because of reduced exposure to the virus and lack of vaccination; these groups also experience greater morbidity with infection than children.

A universal program vaccinating young children and adolescents against varicella offers the best current option to reduce morbidity and mortality from this disease in Australia. Ongoing surveillance of varicella and herpes zoster in Australia and elsewhere will reveal whether there is a need for further interventions, such as a second dose of varicella vaccine in children and high-dose varicella vaccine to prevent herpes zoster in older adults.