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Letter to the Editor
Editor, – Despite the risks, the article 'Frequently asked questions about varicella vaccine' (Aust Prescr 2005;28:2-5) recommends widescale immunisation. There are three arguments against this strategy. Firstly, vaccine immunity may wane over time leaving susceptible adults. Secondly, immunising part of the population may shift the disease burden to those who are not vaccinated and because they will be less likely to acquire chickenpox in childhood they risk more severe disease in adulthood. Thirdly, the effect of vaccination on the incidence of herpes zoster is unknown.
The data so far show that chickenpox in immunised individuals is less severe. However, it is too early to know how this will change as immunised infants reach adulthood.
In 2000 mathematical modelling showed that immunising 90% of infants would produce an initial 'honeymoon' period of low incidence, one or more post-honeymoon epidemics in adolescents and young adults 10-20 years later, and an equilibrium reached after 20-40 years in which the incidence in adults is similar to that in the pre-vaccine years.1 The evidence from the USA on reduced incidence in all age groups covers only five years of experience, which is within the honeymoon period predicted by the modelling. This is insufficient time for epidemics in adults to occur through the build-up of susceptible people, as partial population immunity increases the interepidemic interval.
The impact of varicella vaccine on herpes zoster is complex. There is reasonable evidence that adults exposed to children, or exposed to chickenpox, have less chance of developing zoster, through presumed immunologic boosting by exposure to varicella zoster virus.2 Modelling shows that immunisation causes an increase in herpes zoster for up to 50 years until immunised infants reach old age.
Due to the infectivity of reactivated herpes zoster it is not possible to eliminate varicella zoster virus in the way measles or polio could be eliminated completely. The aim of immunisation is therefore to reduce the burden of varicella disease rather than disease elimination. Since the burden of serious disease, particularly mortality, is in adults, and the modelling shows that in the long term the incidence in adults will not be affected by even high levels of vaccination coverage, the logic of universal vaccination has to be questioned.
Vaccination undoubtedly reduces childhood disease and saves the costs of medical care, childcare costs and lost income for parents while they look after sick children. Health decisions, however, should be primarily based on health considerations rather than economics.
The current low burden of disease from varicella means that it would take only a small rise in varicella in adults for us to be worse off than we were without the vaccine.
General practitioner and Lecturer in epidemiology
Centre for Clinical Epidemiology and Biostatistics
University of Newcastle
- Brisson M, Edmunds WJ, Gay NJ, Law B, De Serres G. Modelling the impact of immunization on the epidemiology of varicella zoster virus. Epidemiol Infect 2000;125:651-69 .
- Thomas SL, Wheeler JG, Hall AJ. Risk factors for herpes zoster in immunocompetent adults. J Epid Community Health 2001;55(Suppl 1):108 .
- Jumaan AO, Yu O, Jackson LA, Bohlke K, Galil K, Seward JF. Incidence of herpes zoster, before and after varicella-vaccination-associated decreases in the incidence of varicella, 1992-2002. J Infect Dis 2005;191:2002-7.
- Oxman MN, Levin MJ, Johnson GR, Schmader KE, Straus SE, Gelb LD, et al. A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults. N Engl J Med 2005;352:2271-84.