Varicella-zoster virus infection in Australia

Burden of varicella in the Asia-Pacific region: a systematic literature review

INTRODUCTION

Varicella is a highly contagious infection that can lead to serious complications, particularly in high-risk groups; however, it is vaccine preventable. Disease awareness and understanding of the disease burden can strongly influence vaccine coverage. This review provides insight into the current epidemiology and the importance of varicella from both public health and economic perspectives across the Asia-Pacific (APAC) region. Areas covered: A systematic literature review was conducted to identify studies on the incidence, seroprevalence, fatality rate and complication rate of varicella. Economic burden studies were also captured. Altogether, 125 studies were identified across the region; these were supplemented by government reports (gray data). Reported vaccine coverage varied from 2.8% to 97%; a key influencing factor was inclusion of the varicella vaccine in national immunization programs. In general, varicella incidence in the unvaccinated population was highest in children ≤5 years old and seroprevalence increased with age. Economic analyses highlighted the cost-saving potential of vaccination programs, especially from a societal perspective. Expert opinion: Varicella-related data varied greatly across the APAC region, highlighting the need to better understand the burden of varicella in this area, and particularly identified the need for better surveillance and reporting.

Epidemiology and factors influencing varicella infections in tropical countries including Sri Lanka

Varicella zoster virus (VZV) infections occur worldwide but the epidemiology differs between different geographical regions. Epidemiology of varicella is partly understood in tropical and subtropical regions. Various hypotheses showing differences in exposure rates in different age groups have been proposed. Exposure to VZV during late childhood or adolescent stage causes high morbidity, especially in high school children, university students and young work force in tropical nations. Exposure to VZV infection or sero-prevalence rates through anti-VZV immunoglobulin G appears to be lower in Sri Lanka, similar to other tropical countries prior to the millennium. In contrast, a more recent study in a group of antenatal women showed a relatively higher exposure rate to VZV when compared to the exposure rates prior to 2004 in Sri Lanka. Climatic factors, socioeconomic conditions, mobility and cultural practices appear to play a role in the differences in the exposure rates to VZV infection in the tropics. In most tropical Asian countries including Sri Lanka, routine vaccination against varicella is not carried out. Individuals with negative history for varicella take the vaccine when there is a necessity. Medical and nursing students take the vaccine prior to their clinical training to avoid adulthood varicella.

Looking back to move forward: a twenty-year audit of herpes zoster in Asia-Pacific

Background

Herpes zoster (HZ) is a prevalent viral disease that inflicts substantial morbidity and associated healthcare and socioeconomic burdens. Current treatments are not fully effective, especially among the most vulnerable patients. Although widely recommended, vaccination against HZ is not routine; barriers in Asia-Pacific include long-standing neglect of adult immunisation and sparse local data. To address knowledge gaps, raise awareness, and disseminate best practice, we reviewed recent data and guidelines on HZ from the Asia-Pacific region.

Methods

We searched PubMed, Scopus, and World Health Organization databases for articles about HZ published from 1994 to 2014 by authors from Australia, China, Hong Kong, India, Indonesia, Japan, Korea, Malaysia, New Zealand, the Philippines, Singapore, Taiwan, Thailand, and Vietnam. We selected articles about epidemiology, burden, complications, comorbidities, management, prevention, and recommendations/guidelines. Internet searches retrieved additional HZ immunisation guidelines.

Results

From 4007 retrieved articles, we screened-out 1501 duplicates and excluded 1264 extraneous articles, leaving 1242 unique articles. We found guidelines on adult immunisation from Australia, India, Indonesia, Malaysia, New Zealand, the Philippines, South Korea, and Thailand.

HZ epidemiology in Asia-Pacific is similar to elsewhere; incidence rises with age and peaks at around 70 years – lifetime risk is approximately one-third. Average incidence of 3–10/1000 person-years is rising at around 5% per year. The principal risk factors are immunosenescence and immunosuppression. HZ almost always causes pain, and post-herpetic neuralgia is its most common complication. Half or more of hospitalised HZ patients have post-herpetic neuralgia, secondary infections, or inflammatory sequelae that are occasionally fatal. These disease burdens severely diminish patients’ quality of life and incur heavy healthcare utilisation.

Conclusions

Several countries have abundant data on HZ, but others, especially in South-East Asia, very few. However, Asia-Pacific countries generally lack data on HZ vaccine safety, efficacy and cost-effectiveness. Physicians treating HZ and its complications in Asia-Pacific face familiar challenges but, with a vast aged population, Asia bears a unique and growing burden of disease. Given the strong rationale for prevention, most adult immunisation guidelines include HZ vaccine, yet it remains underused. We urge all stakeholders to give higher priority to adult immunisation in general and HZ in particular.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2198-y) contains supplementary material, which is available to authorized users.

Microbiology laboratory and the management of mother-child varicella-zoster virus infection

Varicella-zoster virus, which is responsible for varicella (chickenpox) and herpes zoster (shingles), is ubiquitous and causes an acute infection among children, especially those aged less than six years. As 90% of adults have had varicella in childhood, it is unusual to encounter an infected pregnant woman but, if the disease does appear, it can lead to complications for both the mother and fetus or newborn. The major maternal complications include pneumonia, which can lead to death if not treated. If the virus passes to the fetus, congenital varicella syndrome, neonatal varicella (particularly serious if maternal rash appears in the days immediately before or after childbirth) or herpes zoster in the early years of life may occur depending on the time of infection. A Microbiology laboratory can help in the diagnosis and management of mother-child infection at four main times: (1) when a pregnant woman has been exposed to varicella or herpes zoster, a prompt search for specific antibodies can determine whether she is susceptible to, or protected against infection; (2) when a pregnant woman develops clinical symptoms consistent with varicella, the diagnosis is usually clinical, but a laboratory can be crucial if the symptoms are doubtful or otherwise unclear (atypical patterns in immunocompromised subjects, patients with post-vaccination varicella, or subjects who have received immunoglobulins), or if there is a need for a differential diagnosis between varicella and other types of dermatoses with vesicle formation; (3) when a prenatal diagnosis of uterine infection is required in order to detect cases of congenital varicella syndrome after the onset of varicella in the mother; and (4) when the baby is born and it is necessary to confirm a diagnosis of varicella (and its complications), make a differential diagnosis between varicella and other diseases with similar symptoms, or confirm a causal relationship between maternal varicella and malformations in a newborn.

Epidemiological Study on the Incidence of Herpes Zoster in Nearby Cheonan

Background

Herpes Zoster is a disease that occurs after the virus is reactivated due to infection of the varicella virus in childhood. Risk factors are advanced age, malignant neoplasm, organ transplantation, immunosuppressive agents taking are known. The purpose of this study was to investigate the relationship between the seasonal effect and other risk factors on the incidence of herpes zoster.

Methods

The medical records of 1,105 patients admitted to the outpatient diagnosed with herpes zoster were retrospectively examined. The patients' sex, age, dermatome, onset, underlying disease, residential areas were collected.

Results

The incidence of women outnumbered men and increased for those above the age of 50. The number of occurrences of herpes zoster patients was higher in the spring and summer than in winter. Unlike men, women had the most frequent outbreaks in March. The most common occurrence of dermatome is in the thoracic region. The number of occurrence was similar on the left as the right.

Conclusions

In this study, herpes zoster occurs more often in women than in men and more frequently occurs in women in the spring and summer.

Herpes zoster-associated mortality in Europe: a systematic review

Background

Reactivation of latent varicella zoster virus, partly due to age-related immunosenescence and immunosuppressive conditions, results in herpes zoster (HZ) and its associated complications. The management of the most important complication, post-herpetic neuralgia (PHN), is challenging, particularly in the elderly, and is generally unsatisfactory. No previous reviews have reported the incidence of HZ-associated mortality.

Methods

We carried out a systematic literature review to identify studies and databases providing data for HZ-associated mortality in adults aged ≥50 years in Europe.

Results

We identified 12 studies: Belgium (1); France (1); Germany (1); the Netherlands (2); Portugal (1); Spain (4) and England/Wales (2) and 4 databases from Europe: France; Germany and England/Wales. The incidence was available from eight studies; it was highest in those aged ≥95 in France (19.48/100,000). In the European (WHO) database, the overall mortality ranged from 0 to >0.07/100,000. The age- and gender-specific HZ mortality rates from the other databases showed that while in younger age groups the HZ mortality rate was higher in males, in older patients the rate was much higher in women. The case fatality rate was 2 and 61/100 000 in those 45–65 and ≥65 years, respectively. A similar increase with age was seen for the hospital fatality rate; 0.6% in those 45–65 years in the UK and 7.1% in those ≥80 in Spain.

Conclusions

Although the data were sparse and heterogeneous, HZ-associated mortality clearly increases with age. In addition, the elderly who develop HZ often have underlying diseases and are at increased risk of functional decline and loss of independence. Mortality should be taken into account in health-economics models.

Periodicity of varicella-zoster virus in the presence of immune boosting and clinical reinfection with varicella

BACKGROUND

Clinical reinfection with varicella is normally ignored in mathematical transmission models as it is considered too rare to be important.

METHODS

We apply basic bifurcation analysis to a simple mathematical model of varicella-zoster virus (VZV) transmission incorporating reinfection.

RESULTS

We demonstrate that under certain conditions this model can exhibit periodic behaviour as opposed to what is observed in VZV models that ignore the possibility of repeat varicella attacks. Periodicity can be induced by a combination of immune boosting and reinfection while the impact of zoster (shingles) recurrence on the onset of periodicity is negligible.

CONCLUSIONS

Our results suggest that mathematical models of VZV may benefit from inclusion of repeat varicella.

Changes in patterns of hospitalized children with varicella and of associated varicella genotypes after introduction of varicella vaccine in Australia

BACKGROUND

Varicella in children, although usually mild, can cause hospitalization and rarely death. This study examined patterns of hospitalized children with varicella, and associated varicella genotypes, in 4 tertiary children's hospitals throughout Australia before and after varicella vaccine was introduced.

METHODS

We obtained coded data on discharge diagnoses from each hospital before (1999 to 2001) and after (2007 to 2010) varicella vaccine introduction in 2005, adding active surveillance to capture clinical features, complications and immunization history in the latter period. Varicella vesicles were swabbed, and genotyping of varicella strains was performed by real-time polymerase chain reaction amplification.

RESULTS

Overall, a 68% reduction in coded hospitalizations (varicella, 73.2% [P < 0.001]; zoster, 40% [P = 0.002]) occurred post-vaccine introduction. Of children with detailed clinical data (97 varicella and 18 zoster cases), 46 (40%) were immunocompromised. Only 6 of 32 (19%) age-eligible immunocompetent children were immunized. Complications, most commonly secondary skin infections (n = 25) and neurologic conditions (n = 14), occurred in 44% of children. There were no deaths; but 3 immunocompetent unimmunized children had severe multiple complications requiring intensive care. All strains genotyped were "wild-type" varicella, with Clade 1 (European origin) predominating.

CONCLUSIONS

After the introduction of varicella vaccine, coverage of greater than 80% at 2 years of age was achieved, with varicella hospitalizations reduced by almost 70%. Of hospitalized children age-eligible for varicella vaccine, 80% were unimmunized, including all cases requiring intensive care.

Herpes zoster in Australia: evidence of increase in incidence in adults attributable to varicella immunization?

Rates of herpes zoster (HZ) hospitalizations, antiviral prescriptions, and New South Wales emergency-department presentations for age groups <20, 20-39, 40-59 and ⩾60 years were investigated. Trends were analysed using Poisson regression to determine if rates increased following funding of varicella immunization in Australia in November 2005. The regression analysis revealed significantly increasing trends of between 2% and 6% per year in both antiviral prescriptions and emergency-department presentations in all except the <20 years age group. When considered together, the differential changes in rates observed by age group provides preliminary evidence to indicate that HZ incidence is increasing in adults aged >20 years. However, it is not possible to attribute the increasing trends in HZ observed directly to the varicella immunization programme, and continued monitoring and analyses of data for a longer duration, both pre- and post-vaccine introduction, is required.

Hospitalizations to treat herpes zoster in older adults: causes and validated rates

BACKGROUND

The availability of a vaccine for the prevention of herpes zoster has increased interest in methods to measure zoster disease burden. Hospitalizations assigned a zoster diagnosis code have been used as indicators of severe zoster in prior studies. However, a zoster diagnosis code may not be a specific indicator of severe zoster illness, because the code may be assigned to a hospitalization for another cause in a person with coincident zoster.

METHODS

To assess the validity of a hospital diagnosis code of zoster as an indicator of hospitalizations that are attributable to zoster, we identified all hospitalizations with a zoster diagnosis code assigned in any position among members of a managed-care organization who were >or=50 years of age during 1992-2004. Of those, we selected a sample of 260 hospitalizations for chart review.

RESULTS

Chart reviews were completed for 225 hospitalizations. Sixty-five (29%) were because of zoster or a complication of zoster treatment, and an additional 9 (4%) were because of postherpetic neuralgia or a complication of postherpetic neuralgia treatment. Although the overall age-adjusted rate of hospitalizations with a zoster diagnosis code was 42.5 hospitalizations per 100,000 population per year, the estimated rate of hospitalizations because of zoster, postherpetic neuralgia, or adverse effects of a medication used to treat zoster or postherpetic neuralgia was only 14.0 hospitalizations per 100,000 population per year.

CONCLUSIONS

Rates of hospitalizations associated with a zoster diagnosis code will substantially overestimate the burden of hospitalizations attributable to zoster in older adults.

Varicella immunisation practice: Implications for provision of a recommended, non-funded vaccine

AIM

In Australia in 2003 a two-tiered immunisation schedule was introduced consisting of funded (National Immunisation Program) and non-funded but recommended vaccines (Best Practice Schedule), including varicella vaccine. The aim of this study was to examine immunisation practice when a vaccine is recommended but not funded by Government.

METHODS

A survey was sent to 600 randomly selected general practitioners (GPs) in South Australia between June and August 2005, prior to provision of Federal funding for varicella vaccine.

RESULTS

Although varicella was considered an important disease to prevent by 89% of GPs, only 25% of GPs always discussed the non-funded immunisation with parents at the time of a routine immunisation visit. Female GPs were more likely to discuss immunisation with recommended, non-funded vaccines than male GPs. Those who were supportive of varicella prevention were more likely to discuss immunisation with the non-funded vaccine. GPs who always provided information about the disease were more likely to have parents accept their advice about varicella vaccine (62.7%) than those who never provided information (40%). GPs reported parental refusal of varicella vaccine was due to the cost and perception that varicella is a mild disease.

CONCLUSIONS

The results of this study showed variability in prescribing practices for a non-funded vaccine. Recommending a vaccine without provision of funding may lead to 'mixed messages' for immunisation providers and parents with resultant low coverage. Funding a vaccine is likely to reduce variability in provision of the vaccine and improve coverage in the community.

Herpes zoster burden of illness and health care resource utilisation in the Australian population aged 50 years and older

Incidence of zoster and post-herpetic neuralgia (PHN) and associated health care resource utilisation were investigated in the Australian population aged > or =50 years, using general practice data from 2000 to 2006, and pharmaceutical prescribing, hospital morbidity and emergency department data from 1998 to 2005. Zoster and PHN incidence rates were estimated as approximately 10/1000 and 1.45/1000 persons, respectively, with antivirals prescribed for 73.5% of zoster cases. Estimated hospitalisation and emergency department visit rates were 0.67/1000 and 0.38/1000 persons, respectively. Management of zoster (including PHN) involved approximately 2.4 general practitioner consultations. Total costs to the health care system were estimated as approximately 32.8 million per year. The substantial burden of zoster and PHN highlights the potential benefit of zoster vaccination.

Cost-effectiveness of varicella vaccination programs: an update of the literature

Varicella is one of the most common infectious diseases in childhood, caused by the varicella zoster virus. Although vaccines are available, there are only a few countries with an early-childhood vaccination program. Most countries mainly focus on vaccination of high-risk groups, such as susceptible healthcare workers. One of the main concerns with a routine early-childhood vaccination program is a potential (temporal) increase of the incidence of herpes zoster among elderly adults. In this review, we focus on the cost-effectiveness of varicella vaccination and on the methodology used in the health-economic studies. In particular, we focus on the perspective adopted, type of model used, the modeled effect on herpes zoster, the vaccine efficacy and price, and on the value of time lost by infection. The vast majority of studies show vaccination of high-risk groups - including susceptible adolescents - to be cost saving. Routine early-childhood vaccination programs are always cost saving if indirect costs of production losses are included, or cost effective, as long as the potential negative effects on zoster are not taken into account. We note that most studies included in the review used old vaccine prices and a single dose of the varicella vaccine, whereas multiple doses are now becoming the standard. Despite that, those aspects limit the timeliness of our review and we believe that the current work does provide useful insights in the cost-effectiveness of varicella vaccination.

Varicella and the pregnant woman: prevention and management

Infection with varicella zoster virus (VZV) is often considered a childhood 'right of passage'; however, primary infection occurring in women of child-bearing age can have significant adverse consequences both for the mother and for her fetus. During the first trimester, primary VZV infection may result in stillbirth or a baby born with the stigmata of the congenital varicella syndrome, while infection in the peripartum period can result in neonatal varicella, which carries a significant mortality rate despite appropriate antiviral therapy. Varicella in pregnant women can progress to pneumonitis and other severe sequelae that may also compromise the viability of the fetus. Exposure to VZV most commonly occurs in the community or from children in the household, but occasionally, exposure may occur in the hospital environment. Determining a woman's serostatus prior to pregnancy is advised, as effective vaccines are now available and should be administered to non-pregnant seronegative women of child-bearing age. Clinical practice guidelines for management of a pregnant woman exposed to VZV are presented.

The impact of the varicella vaccination program on herpes zoster epidemiology in the United States: a review

Speculation that a universal varicella vaccination program might lead to an increase in herpes zoster (HZ) incidence has been supported by modeling studies that assume that exposure to varicella boosts immunity and protects against reactivation of varicella-zoster virus (VZV) as HZ. Such studies predict an increase in HZ incidence until the adult population becomes predominantly composed of individuals with vaccine-induced immunity who do not harbor wild-type VZV. In the United States, a varicella vaccination program was implemented in 1995. Since then, studies monitoring HZ incidence have shown inconsistent findings: 2 studies have shown no increase in overall incidence, whereas 1 study has shown an increase. Studies from Canada and the United Kingdom have shown increasing rates of HZ incidence in the absence of a varicella vaccination program. Data suggest that heretofore unidentified risk factors for HZ also are changing over time. Further studies are needed to identify these factors, to isolate possible additional effects from a varicella vaccination program. Untangling the contribution of these different factors on HZ epidemiology will be challenging.

Varicella vaccination in Australia and New Zealand

Varicella-zoster virus has been responsible for a significant disease burden, including hospitalizations and deaths in Australia and New Zealand. Varicella vaccine has been available in Australia since 1999 and, since November 2005, has been funded under the National Immunisation Program for use in all children as a single dose at 18 months of age and in a school-based catch-up program at 10-13 years of age. Recent hospitalization data from Australia show a decline in varicella hospitalizations in children 1-4 years of age, most likely related to vaccination. In New Zealand, varicella vaccine has been available since 1999 but is currently not recommended or funded on the New Zealand national immunization schedule. The anticipated licensure of combination measles-mumps-rubella-varicella vaccines in both countries may lead to future schedule changes.

A new challenge for Europe: introducing a pediatric quadrivalent vaccine for measles, mumps, rubella, and varicella

BACKGROUND

Varicella is often considered to be a benign disease of childhood. In fact, varicella is associated with serious complications and mortality even among healthy individuals.

DISCUSSION

Although the course of varicella can be uncomplicated, it can also be associated with serious complications such as pneumonia, fluid and electrolyte disturbances, skin and soft tissue infections and central nervous system disturbances. Worldwide studies have confirmed the high frequency of disease as well as the resultant morbidity, mortality and medical resource use. A quadrivalent vaccine is now available in certain countries to protect against measles, mumps, rubella and varicella (MMRV). Countries that have initiated routine vaccination pro- grams have reported substantial reductions in morbidity and mortality as well as improved health outcomes. The MMRV vaccine facilitates coverage against all four diseases, and would be expected to improve compliance as well as coverage of varicella.

CONCLUSIONS

Universal vaccination programs with MMRV should be considered as a way to reduce the medical and economic impact of varicella. The MMRV vaccine provides a means to achieve universal coverage.

An outbreak of chickenpox at a child care centre in Western Australia. Costs to the community and implications for vaccination policy

OBJECTIVE

Between May and June 2002 an outbreak of chickenpox (CP) occurred at a child care centre in Perth, Western Australia. An epidemiological study was undertaken in order to determine the characteristics of the outbreak, assess vaccine effectiveness, and to define the direct and indirect costs associated with CP infections in young children.

METHODS

A cohort study of the outbreak utilising attendance records and a telephone survey of parents was conducted.

RESULTS

Of the 211 children attending the child care centre at the time of the outbreak, 44 contracted CP (attack rate 25.7%). In addition, two staff members, five secondary household contacts (secondary attack rate 38.5%) and four secondary non-household associated contacts were infected. There were no severe complications or any hospitalisations recorded in infected persons. Two cases had been vaccinated previously. Vaccine effectiveness for CP of any severity was 78.0% (95% CI 15.4-94.3%) while vaccine effectiveness against severe CP was 100%. Direct costs during this outbreak were estimated to be $54 per case and the total costs, including cost of parental time off work or study, were estimated to be $525.73 per case.

CONCLUSIONS AND IMPLICATIONS

Although morbidity associated with CP in young children is not great, infection in childhood is almost universal. This study found that the average costs associated with each CP case were considerable. Since varicella vaccine affords good protection against CP, the recent inclusion of this vaccine in the Australian childhood vaccination schedule should save the community a considerable amount in direct and indirect costs if high coverage rates can be achieved.

Varicella

Varicella-zoster virus, a herpesvirus, causes varicella (chickenpox) and, after endogenous reactivation, herpes zoster (shingles). Varicella, which is recognised by a characteristic vesicular rash, arises mainly in young children, although older individuals can be affected. In immunocompetent patients, symptoms are usually mild to moderate, but an uncomplicated severe case can have more than 1000 lesions and severe constitutional symptoms. Serious complications--including central nervous system involvement, pneumonia, secondary bacterial infections, and death--are sometimes seen. Varicella can be prevented by vaccination. Vaccine is about 80-85% effective against all disease and highly (more than 95%) effective in prevention of severe disease. In the USA, a routine childhood immunisation programme has reduced disease incidence, complications, hospital admissions, and deaths in children and in the general population, indicating strong herd immunity. Similar immunisation programmes have been adopted by some other countries, including Uruguay, Germany, Taiwan, Canada, and Australia, and are expected to be implemented more widely in future.

Uptake of varicella vaccine—a cross sectional survey of parental attitudes to nationally recommended but unfunded varicella immunisation

The aim of this study was to assess the uptake of varicella vaccine in South Australian children under circumstances where varicella immunisation is recommended, but is not funded by Government. The study examined the main reasons that determined a parent's decision whether or not to have their child immunised with varicella vaccine. A cross-sectional survey was conducted by Computer Aided Telephone Interviews (CATI) in June 2004. Data were obtained from 613 households containing 1148 children aged from birth to 17 years of age. Statistical analyses were performed using data weighted to the South Australian population. Six hundred and eighty children (55.7%) had a history of varicella infection and 446 children (42.0%) had received varicella vaccine (weighted data). The most common reasons cited for not having children immunised included lack of knowledge about the vaccine and cost. One year after inclusion of varicella vaccine in the Australian Standard Vaccination Schedule there is evidence of incomplete coverage in children in South Australia due to absence of government funding for vaccine provision.

Determining the rate of varicella vaccine rash in children with moderate-severe eczema

OBJECTIVES

To determine the rate and severity of vesicular reactions following varicella vaccine in children with moderate-severe eczema. Secondary endpoints included the rates and severity of local reactions and eczema severity change within 42 days of vaccination.

METHODS

Prospective open intervention pilot study of varicella vaccine in children aged 12 months to 13 years with moderate-severe eczema. Children were given varicella vaccine alone and followed for 42 days after vaccination.

RESULTS

Fifty children, aged 12 months to 10.5 years were recruited, with complete follow-up for 48. A vesicular rash with a single lesion occurred in one child (2.1% (95% CI: 0, 11.1%)), 10 days following vaccination. Local reactions, including erythema, swelling and tenderness, were reported in eight children (16.7%). A flare-up of moderate-severe generalized eczema was reported in one child (2.1%) during the first week following varicella vaccine.

CONCLUSIONS

Vesicular rash and local reactions following varicella vaccination were no more common or severe in children with moderate-severe eczema than that reported in the published literature in children without eczema. Eczema in the 42 days following vaccination did not appear to increase in severity.

The changing epidemiology of chickenpox in Alberta

BACKGROUND

Varicella vaccine was licensed in Canada in 1998. The province of Alberta introduced a universal publicly funded varicella vaccination program in 2001.

PURPOSE

To describe the epidemiology of non-fatal cases of chickenpox for which publicly funded health services were utilized for the period 1986-2002.

METHODS

We used the records of Alberta's universal, publicly funded health care insurance system to identify cases of chickenpox for the period 1986-2002. The earliest dated utilization of a health service for which there was an ICD9-CM code of 052.xx or an IC10-CA code of B01.xx was used as the date of illness onset. Denominators for rates were estimated using mid-year population estimates from the Alberta Health Care Insurance Registry. Age-specific rates were estimated for each year.

RESULTS

The crude incidence of chickenpox significantly declined over the period 1994-2002, most steeply after the year 2000. The incidence of chickenpox varied by age group and year and there was evidence of age-group-year interaction. Among those aged 5-19 years, chickenpox incidence began to decline prior to vaccine licensure in Canada. Among those aged less than one year and those aged 1-4 years, the incidence increased until 1999 when a decline began. Over the period 0.8% of cases were hospitalized.

CONCLUSION

Chickenpox rates began to decline prior to the introduction of the publicly funded vaccination program; however the declines in rates among the youngest age-groups are consistent with a vaccination program effect.

Varicella vaccination in Australia

Varicella zoster virus (VZV) causes both chickenpox and herpes zoster and is responsible for a significant disease burden, including hospitalizations and deaths, in Australian children and adults. Varicella vaccine has been available in Australia for 5 years; however, from November 2005, it will be funded for use in all susceptible children at 18 months and 10-13 years of age under the National Immunisation Program. Experience with universal varicella vaccination of children in the USA over the last 10 years has shown that the vaccine is safe and highly effective in reducing varicella-related disease. This review summarizes the epidemiology of VZV-related disease in Australia, the use of varicella vaccine and the international experience with vaccine efficacy and safety. The potential impact of varicella vaccination on the incidence of herpes zoster is also discussed.

Decline in mortality due to varicella after implementation of varicella vaccination in the United States

BACKGROUND

Varicella disease has been preventable in the United States since 1995. Starting in 1999, active and passive surveillance data showed sharp decreases in varicella disease. We reviewed national death records to assess the effect of the vaccination program on mortality associated with varicella.

METHODS

Data on deaths for which varicella was listed as an underlying or contributing cause were obtained from National Center for Health Statistics Multiple Cause-of-Death Mortality Data for 1990 through 2001. We calculated the numbers and rates of death due to varicella according to age, sex, race, ethnic background, and birthplace.

RESULTS

The rate of death due to varicella fluctuated from 1990 through 1998 and then declined sharply. For the interval from 1990 through 1994, the average number of varicella-related deaths was 145 per year (varicella was listed as the underlying cause in 105 deaths and as a contributing cause in 40); it then declined to 66 per year during 1999 through 2001. For deaths for which varicella was listed as the underlying cause, age-adjusted mortality rates dropped by 66 percent, from an average of 0.41 death per 1 million population during 1990 through 1994 to 0.14 during 1999 through 2001 (P<0.001). This decline was observed in all age groups under 50 years, with the greatest reduction (92 percent) among children 1 to 4 years of age. In addition, by the period from 1999 through 2001, the average rates of mortality due to varicella among all racial and ethnic groups were below 0.15 per 1 million population, as compared with rates ranging from 0.37 per 1 million for whites to 0.66 per 1 million for other races in the period from 1990 through 1994.

CONCLUSIONS

The program of universal childhood vaccination against varicella in the United States has resulted in a sharp decline in the rate of death due to varicella.

The impact of varicella vaccination in the United States

The addition of varicella vaccine to the universal childhood immunization schedule in the United States in 1995 can be seen as a bold step. Shown to be safe and efficacious against varicella in extensive prelicensure studies, it is nonetheless the first vaccine against a herpesvirus and, furthermore, it is a live, attenuated vaccine. Both wild-type and vaccine strain varicella zoster virus (VZV) are noteworthy for their ability to establish latent infection within the host, with the subsequent possibility of reactivation. Therefore, at the population level, a successful vaccination program could result in the eventual displacement of wild-type VZV by the attenuated vaccine virus. The immediate objective of universal vaccination, however, was to reduce the significant morbidity and mortality associated with primary VZV infection. Data now accumulating suggest that the varicella vaccine as used in the United States has so far been highly effective. The challenge for the future is to predict how the resulting substantial reduction in circulation of VZV will affect immunity among both vaccinees and the unvaccinated. Vaccination strategies likely will need to be adjusted as the epidemiology of VZV in the United States continues to evolve.

The burden and cost of hospitalised varicella and zoster in Australian children

BACKGROUND

Economic analyses of varicella-zoster virus (VZV) immunisation are sensitive to the costs of hospitalised cases, so there is a need to validate VZV hospitalisation data.

AIMS

To assess the accuracy of hospital VZV coding data and to apply these parameters to a population-based sample to estimate incidence and costs.

METHODS

A 3-year retrospective chart review from one hospital to document clinical features and validate coding data. A separate 9-year analysis of discharge data from two hospitals draining a defined region of suburban Melbourne, with adjustment for miscoding and estimates of direct hospital costs.

RESULTS

After correction for miscoding, 224 patients were admitted to one hospital over 3 years, 79% with varicella and 21% with zoster. Miscoding resulted in a 15% underestimate of zoster cases and a 4% overestimate of varicella cases. Thirty-six percent of varicella admissions compared to 80% of zoster admissions were immunocompromised and/or had chronic disease. Compared to otherwise-healthy patients, immunocompromised patients were admitted earlier in their illness and had lower complication rates. Forty-two percent of immunocompromised/chronic disease patients with varicella had a known exposure, usually from a family member. The incidence of hospitalised varicella and zoster in under 15-year olds was 15.7 and 1.8 per 100,000 per year, respectively. This suggests that there are 615 varicella hospitalisations and 72 zoster hospitalisations in this age group each year in Australia, at a total direct cost of over 2.2 million AU dollars.

CONCLUSION

These results highlight the considerable burden of hospitalised zoster and the importance of immunising non-immune contacts of immunocompromised individuals. They also support previous estimates of the incidence of hospitalised varicella in Australian children and adolescents, although direct medical costs may be higher than those previously estimated.

What does epidemiology tell us about risk factors for herpes zoster?

Reactivation of latent varicella zoster virus as herpes zoster is thought to result from waning of specific cell-mediated immunity, but little is known about its determinants in individuals with no underlying immunosuppression. We systematically reviewed studies of zoster epidemiology in adults and analysed data from a large morbidity study to identify factors that might be modulated to reduce the risk of zoster. Annual zoster incidence in population-based studies varied from 3.6-14.2/10(3) in the oldest individuals. Risk factors identified in analytical studies that could explain this variation included age, sex, ethnicity, genetic susceptibility, exogenous boosting of immunity from varicella contacts, underlying cell-mediated immune disorders, mechanical trauma, psychological stress, and immunotoxin exposure. Our review highlights the lack of information about risk factors for zoster. We suggest areas of research that could lead to interventions to limit the incidence of zoster. Such research might also help to identify risk factors for age-related immune decline.

Barriers to immunization: attitudes of general practitioners to varicella, the disease and its vaccine

OBJECTIVES

To investigate the attitudes of general practitioners (GPs) to varicella disease and varicella vaccine.

METHODS

A cross-sectional questionnaire was mailed to GPs in Fairfield (located in the south-western suburbs of Sydney, NSW, Australia) to identify attitudes about varicella vaccine, previous experience with varicella disease and the likelihood of prescribing varicella vaccine.

RESULTS

Of 239 questionnaires issued, 160 were returned (67%). The majority (72%) of respondents agreed that varicella vaccine should become part of the immunization schedule. However 12% of GPs did not support vaccination for varicella as they considered it to be a benign self-limiting disease. Respondents who had experience with varicella complications were significantly more likely to recommend universal vaccination (OR 3.36; 95% confidence interval (CI) 1.38-8.19) whereas those respondents who were concerned about side effects of the vaccine were less likely to recommend universal vaccination (OR 0.31; CI 0.15-0.63).

CONCLUSIONS

The majority of GPs are receptive to varicella vaccination becoming part of the immunization schedule. Experience with varicella complications is associated with recommending universal varicella vaccination. General practitioners in this cohort do not consider varicella to be a benign disease, but they are concerned about possible unknown side effects of the vaccine. Public health measures for introducing universal vaccination need to address these concerns.

The management of varicella-zoster virus exposure and infection in pregnancy and the newborn period. Australasian Subgroup in Paediatric Infectious Diseases of the Australasian Society for Infectious Diseases

Zoster immunoglobulin (ZIG) should be offered to pregnant, varicella-seronegative women with significant exposure to varicella-zoster virus (VZV) (chickenpox) infection. Oral aciclovir prophylaxis should be considered for susceptible pregnant women exposed to VZV who did not receive ZIG or have risk factors for severe disease. Intravenous aciclovir should be given to pregnant women who develop complicated varicella at any stage of pregnancy. Counselling on the risk of congenital varicella syndrome is recommended for pregnant women who develop chickenpox. ZIG should be given to a baby whose mother develops chickenpox up to 7 days before delivery or up to 28 days after delivery. Intravenous aciclovir should be given to babies presenting unwell with chickenpox, whether or not they received ZIG. Breastfeeding of babies infected with or exposed to VZV is encouraged. A mother with chickenpox or zoster does not need to be isolated from her own baby. If siblings at home have chickenpox, a newborn baby should be given ZIG if its mother is seronegative. The newborn baby does not need to be isolated from its siblings with chickenpox, whether or not the baby was given ZIG. After significant nursery exposure to VZV, ZIG should be given to seronegative babies and to all babies born before 28 weeks' gestation.

Seroprevalence of varicella zoster virus, parvovirus B19 and Toxoplasma gondii in a Melbourne obstetric population: implications for management

At an antenatal clinic at a Melbourne obstetric hospital, 308 women were questioned about a known past history of infection with varicella zoster virus (VZV), human parvovirus B19 and Toxoplasma gondii. Immunoglobulin G (IgG) concentrations were determined for the 3 infectious agents and a recalled history of infection was compared with the presence of specific antibody. Exactly 66% of women recalled being infected with chickenpox (VZV) and 94% showed serological evidence of past exposure. Although 64% of women had parvovirus specific IgG, only one gave a definite history of past parvovirus infection. None of the 23% of women with evidence of previous exposure to Toxoplasma gondii recalled a past infection. The proportion of antenatal women at risk in this study was used to estimate the potential burden of disease from congenital infections in Australia and to examine implications for management of pregnancies complicated by these 3 infections.

High seroprevalence of antibodies to varicella zoster virus in adult women in a tropical climate

OBJECTIVES

To determine whether the seroprevalence of antibodies to varicella zoster virus (VZV) in adults is similar to that reported in tropical populations elsewhere.

METHODS

We measured the seroprevalence of VZV IgG antibodies, using an enzyme immunoassay (EIA) in women attending an antenatal clinic in an urban centre in tropical Australia.

RESULTS

The overall seroprevalence of VZV antibodies in 298 women was 92% (95% CI 88-95), with no difference between women who spent their childhoods in the tropics and colleagues. None of the overseas-born women was seronegative.

CONCLUSION

The seroprevalence of VZV antibodies in this tropical population in Australia is as high as that reported from temperate regions, suggesting that social and cultural factors and population mobility are more important determinants of age distribution of VZV immunity than tropical climate.

Varicella vaccination of health-care workers

The objective of this open study was to evaluate the response of non-immune health-care workers to two doses of live attenuated varicella vaccine given two months apart. One hundred subjects (58 females; aged 17-49 yr, mean 22.8 yr) received two doses of varicella vaccine. Blood samples for antibody estimation were taken before vaccination, 2 months after the first dose and 6 weeks after the second dose. Reactions were recorded daily in diaries by the vaccinees and controlled by telephone contacts by the investigators. Ninety-four of 99 vaccinees (94.9%, 95% CL 88.6, 98.3) had detectable antibodies after the first dose [titers 4-1024, geometric mean titer (GMT): 53.2 (95% CL 42.4, 66.8)]. After the second dose, all vaccinees had antibodies (100%, 95% CL 96.6, 100.0) [titers 32-2048, GMT: 235.6 (95% CL 199.0, 278.8)]. Mild reactions limited to the injection site occurred in 1 in 4 subjects after each dose. Vesicular rashes occurred in one subject after the 1st dose and in 3 subjects after the 2nd dose, 1 subject was febrile (38.2 degrees C) after the 1st dose. Eighty-one subjects were retested 12 months after the second vaccination. Three had become seronegative (one developed mild varicella 2 months later). Two had boosted their titers (one after mild clinical varicella 1 month earlier, the other after close contact with clinical cases). The GMT of the group had fallen to 83.6 (95% CL 65.4, 106.8). The identification and vaccination of seronegative health-care workers is safe and efficient, and will benefit the workers themselves and the communities in which they work.