Volume 194 - Issue 5
How can we better understand trends in varicella zoster virus-related disease epidemiology?
Authors: Anita E Heywood and Kristine K Macartney
Med J Aust 2011; 194 (5): 268-269. || doi: 10.5694/j.1326-5377.2011.tb02965.x
Published online: 7 March 2011
Published online: 7 March 2011
To the Editor: The article by Nelson and colleagues1 is a welcome contribution to understanding trends in varicella zoster virus (VZV) disease epidemiology in Australia, particularly ambulatory medical attendance, for which few data sources are available. They report a decline in general practitioner encounters for varicella (chicken pox) since the introduction of varicella vaccine that is consistent with the observed 69% reduction in national hospitalisation rates in children aged 1.5 to 4 years seen from January 2006 to June 2008, 2.5 years into the National Immunisation Program (NIP).2
Nelson et al also report a trend towards higher GP encounter rates for herpes zoster (HZ [shingles]) over time. Although it may be tempting to take this rise on face value, additional analyses are required for a full understanding of patterns in HZ-related health care use, particularly accounting for age and changes in the use of prescription medications, including antivirals and opioid analgesics. Increased HZ-related health care use commencing before varicella vaccine availability has been reported in countries with universal vaccination programs, including the United States3 and Australia,4 as well as in countries where varicella vaccination is not recommended universally, including the United Kingdom.5 In Australia, prescribing of antiviral drugs for HZ increased between 1995 and 1999.6 Australia’s ageing population will contribute to the increasing prevalence of HZ over time due to the propensity of the virus to reactivate with advancing age. An analysis that we conducted shows that an increase in crude national hospitalisation rates for HZ preceded varicella vaccine availability, and that there was no increase over time in age-specific and age-standardised rates (National Centre for Immunisation Research and Surveillance, unpublished data). In addition, the suggestion from modelling studies that HZ may increase under a universal varicella vaccination program because of reduced opportunity for immune boosting in adults has yet to be observed in the US, the country with the longest-standing universal program of varicella vaccination.3 These complexities in monitoring VZV-related diseases highlight the need for very sensitive and well validated surveillance systems for both varicella and HZ in Australia.
Although the authors request consideration for a universal HZ vaccination program for those over 65 years, they may not have been aware that since April 2009 The Australian immunisation handbook, ninth edition, online version has had new guidelines on HZ vaccination recommending a single dose of live attenuated VZV vaccine from the age of 60 years.7 In March 2008, the Pharmaceutical Benefits Advisory Committee recommended that this vaccine was suitable for inclusion in the NIP for those aged 60 years, with a catch-up dose for all individuals aged 61 to < 80 years. A decision regarding NIP funding has not been made, possibly because of a shortage of vaccine due to manufacturing problems.
Acknowledgements
The National Centre for Immunisation Research and Surveillance is supported by funding from the Australian Government Department of Health and Ageing and the NSW Health.
References
- Nelson MR, Britt HC, Harrison CM. Evidence of increasing frequency of herpes zoster management in Australian general practice since the introduction of a varicella vaccine. Med J Aust 2010; 193: 110-113.
- Heywood AE, Macartney K, McIntyre P. The impact of varicella vaccination three years into a publicly funded program [abstract]. Public Health Association Australia 12th National Immunisation Conference; 2010 Aug 17-18; Adelaide, Australia. http://www.ncirs.edu.au/news/archive.php#2010 (accessed Feb 2011).
- Jumaan AO, Yu O, Jackson LA, et al. Incidence of herpes zoster, before and after varicella-vaccination-associated decreases in the incidence of varicella, 1992-2002. J Infect Dis 2005; 191: 2002-2007. 0_i1095855
- Carville KS, Riddell MA, Kelly HA. A decline in varicella but an uncertain impact on zoster following varicella vaccination in Victoria, Australia. Vaccine 2010; 28: 2532-2538. 0_i1095857
- Brisson M, Edmunds WJ, Law B, et al. Epidemiology of varicella zoster virus infection in Canada and the United Kingdom. Epidemiol Infect 2001; 127: 305-314. 0_i1095859
- MacIntyre CR, Chu CP, Burgess MA. Use of hospitalization and pharmaceutical prescribing data to compare the prevaccination burden of varicella and herpes zoster in Australia. Epidemiol Infect 2003; 131: 675-682. 0_i1095863
- Australian Government Department of Health and Ageing. 3.26 Zoster (herpes zoster) [updated April 2009]. In: The Australian immunisation handbook 9th ed. Canberra: DoHA, 2008. http://immunise.health.gov.au/internet/immunise/publishing.nsf/Content/Handbook-zoster (accessed Feb 2011).