Postmarketing evaluation of the safety and effectiveness of varicella vaccine

Risk of Inappropriately Timed Live Vaccination After Pediatric Cardiovascular Surgery

OBJECTIVE

The American Academy of Pediatrics (AAP), Advisory Committee on Immunization Practices (ACIP), and Centers for Disease Control and Prevention (CDC) recommend delaying live vaccinations up to 11 months after transfusions of certain blood products due to the risk of immunoglobulins decreasing immunization efficacy. Because vaccination schedules recommend live immunizations at 12 months, infants aged 5 to 12 months who undergo cardiac surgery requiring blood products are potentially at risk for improper vaccination. The objective of this study was to identify the risk of inappropriately timed live vaccination in pediatric patients after cardiovascular surgery.

METHODS

This single-center, retrospective chart review included 345 patients 5 to 12 months of age who underwent cardiovascular surgery between January 1, 2010, and December 31, 2016. Included patients received packed red blood cells (PRBCs) and/or platelets during the surgical admission and a live vaccine within the first 18 months of life. The primary endpoint was the incidence of live vaccine administration within 7 months of receiving PRBCs and/or platelets.

RESULTS

Of the 345 included patients, 67% (n = 230) were inappropriately vaccinated after receiving platelets and/or PRBCs during cardiac surgery.

CONCLUSIONS

Infants who undergo cardiac surgery between the ages of 5 and 12 months are at risk for inappropriate live vaccination timing. A clinically significant percentage of pediatric patients who received blood products during a cardiac surgical admission later received live vaccines at times that were inconsistent with AAP, ACIP, and CDC recommendations. Future interventions aimed at educating providers and patients may be warranted.

Safety surveillance of varicella vaccine using tree-temporal scan analysis

IMPORTANCE

Passive surveillance systems are susceptible to the under-reporting of adverse events (AE) and a lack of information pertaining to vaccinated populations. Conventional active surveillance focuses on predefined AEs. Advanced data mining tools could be used to identify unusual clusters of potential AEs after vaccination.

OBJECTIVE

To assess the feasibility of a novel tree-based statistical approach to the identification of AE clustering following the implementation of a varicella vaccination program among one-year-olds.

SETTING AND PARTICIPANTS

This nationwide safety surveillance was based on data from the Taiwan National Health Insurance database and National Immunization Information System for the period 2004 through 2014. The study population was children aged 12-35 months who received the varicella vaccine.

EXPOSURE

First-dose varicella vaccine.

OUTCOMES AND MEASURES

All incident ICD-9-CM diagnoses (emergency or inpatient departments) occurring 1-56 days after the varicella vaccination were classified within a hierarchical system of diagnosis categories using Multi-Level Clinical Classifications Software. A self-controlled tree-temporal data mining tool was then used to explore the incidence of AE clustering with a variety of potential risk intervals. The comparison interval consisted of days in the 56-day follow-up period that fell outside the risk interval.

RESULTS

Among 1,194,189 varicella vaccinees with no other same-day vaccinations, nine diagnoses with clustering features were categorized into four safety signals: fever on days 1-6 (attributable risk [AR] 38.5 per 100,000, p < 0.001), gastritis and duodenitis on days 1-2 (AR 5.9 per 100,000, p < 0.001), acute upper respiratory infection on days 1-5 (AR 11.0 per 100,000, p = 0.006), and varicella infection on days 1-9 (AR 2.7 per 100,000, p < 0.001). These safety profiles and their corresponding risk intervals have been identified in previous safety surveillance studies.

CONCLUSIONS

Unexpected clusters of AEs were not detected after the mass administration of childhood varicella vaccines in Taiwan. The tree-temporal statistical method is a feasible approach to the safety surveillance of vaccines in populations of young children.

Assessment of pre-specified adverse events following varicella vaccine: A population-based self-controlled risk interval study

BACKGROUND

Clinical trials and spontaneous reporting systems have revealed rare but biologically plausible adverse events following varicella immunization. Few post-marketing controlled studies have been conducted to assess the relationship between the varicella vaccine and these outcomes.

OBJECTIVES

To evaluate the risk of pneumonia, idiopathic thrombocytopenic purpura (ITP), meningitis, encephalitis and ischemic stroke following varicella immunization.

MATERIALS AND METHODS

This nationwide observational study was based on Taiwan National Health Insurance data and National Immunization Information System from 2004 through 2014. Primary analysis included children aged 12-35 months who received the single varicella vaccine on the date of administration. The self-controlled risk interval design compared the incidence of pre-specified outcomes during a risk interval of 1-42 days post-vaccination and a control interval of 43-84 days. The outcomes of interest were defined as admitted pneumonia, ITP, meningitis, encephalitis, and ischemic stroke, as well as fracture as a negative control. Conditional Poisson regression was used to assess the incidence rate ratio (aIRR) with adjustments for age and seasonal effects.

RESULTS

Among 1,194,189 children, who receiving the varicella vaccine, there was no observed increase in the risk for ITP (aIRR 1.00; 95% CI, 0.76-1.33), meningitis (aIRR 1.21; 95% CI, 0.49-2.95), encephalitis (aIRR 1.00; 95% CI, 0.62-1.60), or ischemic stroke (aIRR 1.24; 95% CI, 0.31-4.95). A clustering feature with pneumonia occurred during days 36-42 post-vaccination (aIRR 1.10; 95% CI, 1.02-1.18). An increase in the risk for ITP was observed in children receiving the varicella and MMR vaccines concomitantly (aIRR 1.70; 95% CI, 1.19-2.43), but not among those receiving the varicella vaccine only.

CONCLUSIONS

We detected a small risk of incidental pneumonia associated with varicella vaccine in the 6th week after immunization. There was no increase in the risk of other pre-specified adverse events.

Do varicella vaccination programs change the epidemiology of herpes zoster? A comprehensive review, with focus on the United States

Introduction: Policy-makers in many countries have been wary of introducing varicella vaccination programs because of concerns that reduced exposures to varicella-zoster virus could increase herpes zoster (HZ) incidence. The U.S. introduced varicella vaccination in 1996 and has empiric evidence regarding this concern. Areas covered: This comprehensive review provides background emphasizing the epidemiology of varicella and of HZ in the U.S. before and after the introduction of their respective vaccines. The epidemiology is complex, and interpretation is complicated by methodologic challenges, by unexplained increases in age-specific HZ incidence that preceded varicella vaccination, and by introduction of vaccines for prevention of HZ. Nonetheless, observations from studies using different platforms and designs have yielded consistent findings, suggesting they are robust. Expert opinion: There has been no evidence that the U.S. varicella vaccination program increased HZ incidence in the general adult population over baseline trends. Furthermore, HZ incidence in children is declining. The U.S. experience can inform the development of new generations of models to predict HZ trends. More importantly, it provides reassurance for countries considering varicella vaccination that an effective program can reduce varicella morbidity and mortality while reducing the likelihood of HZ among children, and potentially, over time, across the entire population.

Incidence of Herpes Zoster Among Children: 2003-2014

BACKGROUND AND OBJECTIVES

After the 1996 introduction of routine varicella vaccination in the United States, most studies evaluating pediatric herpes zoster (HZ) incidence reported lower incidence over time, with varying degrees of decline. Using the combined databases of 6 integrated health care organizations, we examined HZ incidence in children over a 12-year period in the varicella vaccine era.

METHODS

This study included children aged 0 through 17 years from 2003 through 2014. Using electronic medical records, we identified HZ cases through International Classification of Diseases, Ninth Revision diagnosis code 053. We calculated HZ incidence rates per 100 000 person years of health plan membership for all children and among children who were vaccinated versus unvaccinated. We calculated rates for the 12-year period and examined temporal trends. Among children who were vaccinated, we compared HZ rates by month and year of age at vaccination.

RESULTS

The study included 6 372 067 children with ≥1 month of health plan membership. For the 12-year period, the crude HZ incidence rate for all subjects was 74 per 100 000 person years, and the rate among children who were vaccinated was 38 per 100 000 person years, which was 78% lower than that among children who were unvaccinated (170 per 100 000 person years; P < .0001). Overall HZ incidence declined by 72% (P < .0001) from 2003 through 2014. Annual rates in children who were vaccinated were consistently lower than in children who were unvaccinated.

CONCLUSIONS

With this population-based study, we confirm the decline in pediatric HZ incidence and the significantly lower incidence among children who are vaccinated, reinforcing the benefit of routine varicella vaccination to prevent pediatric HZ.

Trends in U.S. Community hospitalizations due to herpes zoster: 2001-2015

BACKGROUND

In 2007, based on decisions by the U.S. Advisory Committee on Immunization Practices, the CDC recommended a booster dose at 4-6 years in the varicella vaccine schedule. In 2008, a herpes zoster vaccine was recommended for use in persons age ≥60 years. The purpose of this study was to examine trends in herpes zoster hospitalization rates and assess the impact of both policy recommendations using U.S. hospital discharge data.

METHODS

Nationwide Inpatient Sample discharge data from 2001 to 2015 were used to identify primary or secondary herpes zoster diagnoses. Trends in annual total and age-specific herpes zoster hospitalization rates and average length of stay were examined. Average annual rates for the pre (2001-2005) and post (2012-2015)-zoster vaccine policy eras were compared. Absolute change in herpes zoster hospitalizations were calculated.

RESULTS

The rate difference of U.S. herpes zoster hospitalizations in the post vs. pre-zoster vaccine policy era was -1.9 per 100,000 population (6,200 fewer hospitalizations in 2015 than expected). Key age group rate differences: 0-3 years (-0.4 per 100,000; 50 fewer), 4-6 years (-0.6 per 100,000; 50 fewer), 7-14 years (-1.3 per 100,000; 400 fewer), 50-59 years (0.7 per 100,000; 300 more), 60-69 years (-2.5 per 100,000; 900 fewer), 70-79 years (-10.2 per 100,000; 2,000 fewer), 80+ years (-29.9 per 100,000; 3,600 fewer).

CONCLUSIONS

Reduction of wild-type varicella due to the 2-dose varicella vaccination recommendation may have impacted declining herpes zoster hospitalization rates among children ≤14 years. The 2008 herpes zoster vaccine may have impacted declining herpes zoster hospitalization rates for adults age ≥60 years despite vaccination coverage <31% by 2015.

Effectiveness and impact of a single-dose vaccine against chickenpox in the community of Madrid between 2001 and 2015

BACKGROUND

Chickenpox is a contagious airborne disease. Immunization by varicella vaccine is an effective preventive measure. The objective of this study is to evaluate the impact and effectiveness of a single-dose vaccination against chickenpox at 15 months of age.

METHODS

Observational study based on data from the Epidemiological Surveillance System of the Autonomous Community of Madrid from 2001 to 2015. The years were grouped into 4 periods according to epidemic cycles and vaccination schedule: 2001-06, 2007-10, 2011-13 and 2014-15. The impact was calculated as Relative Risk (RR) between the incidence of chickenpox in children between 15 months and 13 years of age between 2011-13 and 2001-06 through Poisson regression using notifications made to the Diseases of Compulsory Declaration (DCD) system, the Sentinel Physicians Network (SPN) and hospital discharge records noted as Minimum Basic Data Set (MBDS). The vaccine effectiveness (VE) was calculated using the screening method and a 1:2 case-control study paired by age and paediatrician in population from 15 months to 13 years and between 2007 and 2015 using SPN source data.

RESULTS

The RR_{2011-13/2001-06} using data from the DCD was 0.14 (95% CI: 0.14 to 0.15), 0.07 (95% CI: 0.06 to 0.08) from SPN and 0.17 (95% CI: 0.15 to 0.20) from MBDS. A total of 338 cases were included in the VE screening obtaining an overall of 76.7% (IC 95%: 71.9 to 80.7%). For a case-control study, 120 cases and 247 controls were recruited obtaining a VE of 92.4% (IC 95%: 80.8 to 97.0%).

CONCLUSIONS

The single-dose vaccination against chickenpox at 15 months of age has high impact and effectiveness.

Incidence rate of breakthrough varicella observed in healthy children after 1 or 2 doses of varicella vaccine: Results from a meta-analysis

BACKGROUND

Although extensive varicella vaccination coverage has been reported in many countries, breakthrough varicella (BV) still occurs in healthy children. We performed a meta-analysis to understand whether 2 varicella vaccine doses are needed in children and, if so, to determine the best time to vaccinate.

METHODS

The BV incidence rates after 1 or 2 doses of varicella vaccine were pooled using random effects, and 95% confidence intervals (CI) were used to estimate the risk factors after vaccination.

RESULTS

A total of 27 original articles were included in this meta-analysis. The pooled average BV incidence rate in children vaccinated with 1 dose was 8.5 cases per 1,000 person years (PY) (95% confidence interval [CI], 5.3-13.7; random effects model) and 2.2 cases per 1,000 PY (95% CI, 0.5-9.3; random effects model) in children vaccinated with 2 doses. The pooled trend of the annual BV incidence rate from the first to eighth year fluctuated, with a peak annual incidence rate of 35.3 cases per 1,000 population in the fourth year. The meta-regression showed that design type, type of vaccine, and their interaction accounted for approximately 71.74% of the heterogeneity in the average BV incidence rate after 1 vaccine dose.

CONCLUSIONS

Two doses of varicella vaccine are more effective than a single dose, and 3-4 years between the first and second vaccinations may achieve higher efficacy.

Unmasking in an observational vaccine safety study: Using type 2 diabetes mellitus as an example

BACKGROUND

In observational vaccine safety studies, diagnosis codes assigned prior to or on the day of vaccination (Day 0) are often excluded from analysis of safety signals since they usually represent pre-existing conditions. The limitations of this approach have been described for autoimmune conditions but not for other chronic conditions. We draw on our experience in a post-licensure quadrivalent human papillomavirus vaccine (HPV4) safety study to examine the effectiveness of exclusion of pre-existing and Day 0 diagnoses of type 2 diabetes mellitus (T2DM) in excluding prevalent T2DM.

METHODS

Subjects included all 117,402 females ages 9-26 years who received HPV4 August 2006-March 2008 in Kaiser Permanente Southern California. We identified potential incident T2DM cases using ICD9 code 250.xx associated with inpatient and emergency room visits during the 60 days following each HPV4 dose, excluding those with this code prior to their first HPV4 dose. Electronic medical records were reviewed to determine the dates of symptom onset, diagnostic labs, vaccine administration and T2DM diagnosis.

RESULTS

Of 33 potential incident T2DM cases identified using automated data, 4 (12%) were confirmed to have new onset T2DM after medical record review. Nineteen cases were excluded that did not have T2DM or had T2DM diagnosed before Day 0; nine had an abnormal fasting blood sugar (FBS) ordered on Day 0, prompting subsequent evaluation and diagnosis of T2DM; and one had elevated FBS and glucosuria prior to the first dose of HPV4 but T2DM diagnosed at a visit following vaccination.

CONCLUSION

These results suggest that among adolescents and young adults, the workup and subsequent diagnosis of pre-existing conditions may result from a visit at which a vaccination is administered. This "unmasking" phenomenon is not entirely eliminated by exclusion of pre-existing and Day 0 diagnoses. Medical record review should be considered in the evaluation of potential safety signals.

Pharmacovigilance in children: detecting adverse drug reactions in routine electronic healthcare records. A systematic review

AIMS

A systematic review of the literature published in English over 10 years was undertaken in order to describe the use of electronic healthcare data in the identification of potential adverse drug reactions (ADRs) in children.

METHODS

MEDLINE and EMBASE were searched using MESH headings and text words. Titles, keywords and abstracts were checked for age <18 years, potential ADRs and electronic healthcare data. Information extracted included age, data source, pharmacovigilance method, medicines and ADRs. Studies were quality assessed.

RESULTS

From 14 804 titles, 314 had a full text review and 71 were included in the final review. Fifty were published in North America, 10 in Scandinavia. Study size ranged from less than 1000 children to more than 10 million. Sixty per cent of studies used data from one source. Comparative observational studies were most commonly reported (66.2%) with 15% using passive surveillance. Electronic healthcare data set linkage and the quality of the data source were poorly reported. ADRs were classified using the International Classification of Disease (ICD10). Multi-system reactions were most commonly studied, followed by central nervous system and mental and behavioural disorders. Vaccines were most frequently prescribed followed by corticosteroids, general anaesthetics and antidepressants.

CONCLUSIONS

Routine electronic healthcare records were increasingly reported to be used for pharmacovigilance in children. This growing and important health protection activity could be enhanced by consistent reporting of studies to improve the identification, interpretation and generalizability of the evidence base.

Safety of vaccines used for routine immunization of U.S. children: a systematic review

BACKGROUND

Concerns about vaccine safety have led some parents to decline recommended vaccination of their children, leading to the resurgence of diseases. Reassurance of vaccine safety remains critical for population health. This study systematically reviewed the literature on the safety of routine vaccines recommended for children in the United States.

METHODS

Data sources included PubMed, Advisory Committee on Immunization Practices statements, package inserts, existing reviews, manufacturer information packets, and the 2011 Institute of Medicine consensus report on vaccine safety. We augmented the Institute of Medicine report with more recent studies and increased the scope to include more vaccines. Only studies that used active surveillance and had a control mechanism were included. Formulations not used in the United States were excluded. Adverse events and patient and vaccine characteristics were abstracted. Adverse event collection and reporting was evaluated by using the McHarm scale. We were unable to pool results. Strength of evidence was rated as high, moderate, low, or insufficient.

RESULTS

Of 20 478 titles identified, 67 were included. Strength of evidence was high for measles/mumps/rubella (MMR) vaccine and febrile seizures; the varicella vaccine was associated with complications in immunodeficient individuals. There is strong evidence that MMR vaccine is not associated with autism. There is moderate evidence that rotavirus vaccines are associated with intussusception. Limitations of the study include that the majority of studies did not investigate or identify risk factors for AEs; and the severity of AEs was inconsistently reported.

CONCLUSIONS

We found evidence that some vaccines are associated with serious AEs; however, these events are extremely rare and must be weighed against the protective benefits that vaccines provide.

Vaccines for post-exposure prophylaxis against varicella (chickenpox) in children and adults

BACKGROUND

The prevention of varicella (chickenpox) using live attenuated varicella vaccines has been demonstrated both in randomised controlled trials (RCTs) and in population-based immunisation programmes in countries such as the United States and Australia. Many countries do not routinely immunise children against varicella and exposures continue to occur. Although the disease is often mild, complications such as secondary bacterial infection, pneumonitis and encephalitis occur in about 1% of cases, usually leading to hospitalisation. The use of varicella vaccine in persons who have recently been exposed to the varicella zoster virus has been studied as a form of post-exposure prophylaxis (PEP).

OBJECTIVES

To assess the efficacy and safety of vaccines for use as PEP for the prevention of varicella in children and adults.

SEARCH METHODS

We searched CENTRAL (2014, Issue 1), MEDLINE (1966 to March week 1, 2014), EMBASE (January 1990 to March 2014) and LILACS (1982 to March 2014). We searched for unpublished trials registered on the clinicaltrials.gov and WHO ICTRP websites.

SELECTION CRITERIA

RCTs and quasi-RCTs of varicella vaccine for PEP compared with placebo or no intervention. The outcome measures were efficacy in prevention of clinical cases and/or laboratory-confirmed clinical cases and adverse events following vaccination.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted and analysed data using Review Manager software.

MAIN RESULTS

We identified three trials involving 110 healthy children who were siblings of household contacts. The included trials varied in study quality, vaccine used, length of follow-up and outcomes measured and, as such, were not suitable for meta-analysis. We identified high or unclear risk of bias in two of the three included studies. Overall, 13 out of 56 vaccine recipients (23%) developed varicella compared with 42 out of 54 placebo (or no vaccine) recipients (78%). Of the vaccine recipients who developed varicella, the majority only had mild disease (with fewer than 50 skin lesions). In the three trials, most participants received PEP within three days following exposure; too few participants were vaccinated four to five days post-exposure to ascertain the efficacy of vaccine given more than three days after exposure. No included trial reported on adverse events following immunisation.

AUTHORS' CONCLUSIONS

These small trials suggest varicella vaccine administered within three days to children following household contact with a varicella case reduces infection rates and severity of cases. We identified no RCTs for adolescents or adults. Safety was not adequately addressed.

Fever following immunization

Fever is a frequent systemic adverse event following immunization, especially in infants and young children. Any fever after immunization may be caused by immunization or may coincide temporally as an indication of underlying disease, usually an infectious one. The time pattern of fever attributable to immunization has characteristic features depending on the vaccine used. Comparability of fever rates associated with different vaccines, or the same vaccines in different studies, is frequently hampered by the use of different definitions and/or assessment techniques for fever. A recent analysis by the Brighton Collaboration has provided a standardized case definition for fever, the use of which should be strongly encouraged.

Long-term effectiveness of varicella vaccine: a 14-Year, prospective cohort study

BACKGROUND

Varicella vaccine was licensed in the United States in 1995 for individuals ≥12 months of age. A second dose was recommended in the United States in June 2006. Varicella incidence and vaccine effectiveness were assessed in a 14-year prospective study conducted at Kaiser Permanente Northern California.

METHODS

A total of 7585 children vaccinated with varicella vaccine in their second year of life in 1995 were followed up prospectively for breakthrough varicella and herpes zoster (HZ) through 2009. A total of 2826 of these children received a second dose in 2006-2009. Incidences of varicella and HZ were estimated and compared with prevaccine era rates.

RESULTS

In this cohort of vaccinated children, the average incidence of varicella was 15.9 per 1000 person-years, nine- to tenfold lower than in the prevaccine era. Vaccine effectiveness at the end of the study period was 90%, with no indication of waning over time. Most cases of varicella were mild and occurred early after vaccination. No child developed varicella after a second dose. HZ cases were mild, and rates were lower in the cohort of vaccinated children than in unvaccinated children during the prevaccine era (relative risk: 0.61 [95% confidence interval: 0.43-0.89]).

CONCLUSIONS

This study confirmed that varicella vaccine is effective at preventing chicken pox, with no waning noted over a 14-year period. One dose provided excellent protection against moderate to severe disease, and most cases occurred shortly after the cohort was vaccinated. The study data also suggest that varicella vaccination may reduce the risks of HZ in vaccinated children.

Ensuring the optimal safety of licensed vaccines: a perspective of the vaccine research, development, and manufacturing companies

Vaccine safety is increasingly a focus for the general public, health care providers, and vaccine manufacturers, because the efficacy of licensed vaccines is accepted as a given. Commitment to ensuring safety of all vaccines, including childhood vaccines, is addressed by the federal government, academia, and industry. Safety activities conducted by the vaccine research, development, and manufacturing companies occur at all stages of product development, from selection and formulation of candidate vaccines through postlicensure studies and surveillance of adverse-event reports. The contributions of multiple interacting functional groups are required to execute these tasks through the life cycle of a product. We describe here the safeguards used by vaccine manufacturers, including specific examples drawn from recent experience, and highlight some of the current challenges. Vaccine-risk communication becomes a critical area for partnership of vaccine companies with government, professional associations, and nonprofit advocacy groups to provide information on both benefits and risks of vaccines. The crucial role of the vaccine companies in ensuring the optimal vaccine-safety profile, often overlooked, will continue to grow with this dynamic arena.

Varicella vaccination in pediatric kidney and liver transplantation

Reports about efficacy and safety of live-virus attenuated vaccines in patients before and after transplantation are mainly based on small patient numbers, making general recommendations for this patient population difficult. Children and adults as well as their close relatives and contact persons should be preferably immune to VZV before solid organ transplantation to avoid VZV-associated complications, thus making VZV vaccination necessary in susceptible individuals. The following literature review focused on efficacy and safety of VZV vaccination in pediatric kidney and liver transplant recipients. Review of literature also revealed that in all pediatric transplant candidates, humoral and cellular immunity against VZV should be consistently monitored to assess waning immunity under immunosuppressive treatment. This approach is desirable to estimate the risk of severe varicella disease after exposure in these patients.

Incidence of herpes zoster among children vaccinated with varicella vaccine in a prepaid health care plan in the United States, 2002-2008

BACKGROUND

Herpes zoster (HZ), or shingles, is caused by reactivation of latent varicella-zoster virus after a primary infection with either wild-type or vaccine-type varicella-zoster virus, the latter having been introduced in 1995 for children. Since then, few population-based data about the incidence of childhood HZ are available.

METHODS

We identified children aged < or = 12 years who were vaccinated with 1 dose of varicella vaccine between 2002 and 2008 in a prepaid health plan and followed them through their electronic health records for a diagnosis of HZ. The medical records of these children were reviewed. Persistent and chronic conditions for these children before HZ were identified.

RESULTS

There were 172,163 children vaccinated, with overall follow-up of 446,027 person-years (Incidence rate = 27.4 per 100,000 person-years, 95% confidence interval: 22.7-32.7). Children vaccinated after age 5 years had a higher but not statistically significant different rate than children vaccinated between 12 and 18 months (34.3 vs. 28.5 per 100,000 person-years). Among children vaccinated between 12 and 18 months, incidence rates gradually increased each year in the first 4 years after vaccination (P < 0.001). Among the HZ cases, there were 1 (0.7%) case of lymphoid leukemia, 1 (0.7%) case of drug abuse, 16 (11.1%) cases of asthma with 3 or more acute exacerbations, 12 (8.3%) cases of developmental disorders, and 3 (2.1%) cases of psychological or mental disorders.

CONCLUSIONS

These data demonstrate that diagnosed HZ is rare among children following varicella vaccine. Despite the small numbers, the roles of delayed vaccination, severe asthma, and development disorders warrant further investigation. In the future, analyses of HZ isolates will be needed to identify the virus strains causing reactivation.

The incidence and clinical characteristics of herpes zoster among children and adolescents after implementation of varicella vaccination

BACKGROUND

The varicella-zoster virus (VZV) vaccine strain may reactivate to cause herpes zoster. Limited data suggest that the risk of herpes zoster in vaccinated children could be lower than in children with naturally acquired varicella. We examine incidence trends, risk and epidemiologic and clinical features of herpes zoster disease among children and adolescents by vaccination status.

METHODS

Population-based active surveillance was conducted among <20 years old residents in Antelope Valley, California, from 2000 through 2006. Structured telephone interviews collected demographic, varicella vaccination and disease histories, and clinical information.

RESULTS

From 2000 to 2006, the incidence of herpes zoster among children<10 years of age declined by 55%, from 42 cases reported in 2000 (74.8/100,000 persons; 95% confidence interval [95% CI]: 55.3-101.2) to 18 reported in 2006 (33.3/100,000; 95% CI: 20.9-52.8; P<0.001). During the same period, the incidence of herpes zoster among 10- to 19-year-olds increased by 63%, from 35 cases reported in 2000 (59.5/100,000 persons; 95% CI: 42.7-82.9) to 64 reported in 2006 (96.7/100,000; 95% CI: 75.7-123.6; P<0.02). Among children aged<10 years, those with a history of varicella vaccination had a 4 to 12 times lower risk for developing herpes zoster compared with children with history of varicella disease.

CONCLUSIONS

Varicella vaccine substantially decreases the risk of herpes zoster among vaccinated children and its widespread use will likely reduce overall herpes zoster burden in the United States. The increase in herpes zoster incidence among 10- to 19-year-olds could not be confidently explained and needs to be confirmed from other data sources.

Varicella zoster virus vaccines: effective, but concerns linger

Both varicella and herpes zoster (HZ) can cause severe disease in certain age groups. The cell-mediated immune (CMI) response to the varicella zoster virus (VZV) is critical in preventing a recurrence of VZV. The varicella vaccine has markedly decreased the morbidity and mortality associated with varicella, but concerns linger about the cost and frequency of vaccine administration and the long-term effects on both adult varicella and HZ epidemiology in the individual and in the population. Therapy for HZ with an antiviral is only partially effective. A zoster vaccine is now available that boosts the CMI immune reaction to VZV in individuals and has proven safe and partially effective in preventing both HZ and post-herpetic neuralgia. Concerns about the zoster vaccine include the costs of administration, the overall health-care costs to society, and the acceptance and implementation of the vaccine in the elderly. Because of altered immune responses to VZV as a result of universal varicella vaccination it becomes even more compelling in the future to have a zoster vaccine ready to boost the CMI response to a sufficient level to prevent HZ. The 2 vaccines are intertwined in the future epidemiology of VZV disease.

Acyclovir-resistant chronic verrucous vaccine strain varicella in a patient with neuroblastoma

A 21-month-old girl with neuroblastoma developed chronic verrucous Oka strain varicella-zoster infection during chemotherapy. Virus isolated from the patient demonstrated high-level acyclovir resistance, and its thymidine kinase had no in vitro enzymatic activity. After foscarnet therapy, she underwent stem cell transplantation without varicella reactivation. This is only the second reported case of resistant varicella zoster virus caused by Oka strain virus.

Varicella prevention in the United States: a review of successes and challenges

OBJECTIVE

In 1995, the United States was the first country to introduce a universal 1-dose childhood varicella vaccination program. In 2006, the US varicella vaccine policy was changed to a routine 2-dose childhood program, with catchup vaccination for older children. The objective of this review was to summarize the US experience with the 1-dose varicella vaccination program, present the evidence considered for the policy change, and outline future challenges of the program.

METHODS

We conducted a review of publications identified by searching PubMed for the terms "varicella," "varicella vaccine," and "herpes zoster." The search was limited to US publications except for herpes zoster; we reviewed all published literature on herpes zoster incidence.

RESULTS

A single dose of varicella vaccine was 80% to 85% effective in preventing disease of any severity and >95% effective in preventing severe varicella and had an excellent safety profile. The vaccination program reduced disease incidence by 57% to 90%, hospitalizations by 75% to 88%, deaths by >74%, and direct inpatient and outpatient medical expenditures by 74%. The decline of cases plateaued between 2003 and 2006, and outbreaks continued to occur, even among highly vaccinated school populations. Compared with children who received 1 dose, in 1 clinical trial, 2-dose vaccine recipients developed in a larger proportion antibody titers that were more likely to protect against breakthrough disease and had a 3.3-fold lower risk for breakthrough disease and higher vaccine efficacy. Two studies showed no increase in overall herpes zoster incidence, whereas 2 others showed an increase.

CONCLUSIONS

A decade of varicella prevention in the United States has resulted in a dramatic decline in disease; however, even with high vaccination coverage, the effectiveness of 1 dose of vaccine did not generate sufficient population immunity to prevent community transmission. A 2-dose varicella vaccine schedule, therefore, was recommended for children in 2006. Data are inconclusive regarding an effect of the varicella vaccination program on herpes zoster epidemiology.

Vaccines for post-exposure prophylaxis against varicella (chickenpox) in children and adults

BACKGROUND

Live attenuated varicella vaccines for the prevention of varicella (chickenpox) has been demonstrated both in randomised controlled trials (RCTs) and in population-based immunisation programmes in countries such as the United States. However, many countries do not routinely immunise children against varicella, and exposures continue to occur. Although the disease is often mild, complications such as secondary bacterial infection, pneumonitis and encephalitis occur in about 1% of cases, usually leading to hospitalisation. The use of varicella vaccine in persons who have recently been exposed to the varicella zoster virus has been studied as a form of post-exposure prophylaxis (PEP).

OBJECTIVES

To assess the efficacy and safety of vaccines for use as PEP for the prevention of varicella in children and adults.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2008, Issue 1); MEDLINE (1966 to February 2008); and EMBASE (January 1990 to February 2008).

SELECTION CRITERIA

RCTs and quasi-RCTs of varicella vaccine for PEP compared with placebo or no intervention. The outcome measures were efficacy in prevention of clinical cases and/or laboratory-confirmed clinical cases and adverse effects following vaccination.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted and analysed data using Review Manager software.

MAIN RESULTS

Three studies involving 110 healthy children who were siblings of household contacts were identified as suitable for inclusion. The studies varied in quality, study design, vaccine used, and outcomes measured and, as such, were not suitable for meta-analysis. Overall, 13 out of 56 vaccine recipients (18%) developed varicella compared with 42 out of 54 placebo (or no vaccine) recipients (78%). Of the vaccine recipients who developed varicella, the majority only had mild disease (with less than 50 skin lesions). In the three studies, most subjects received PEP within three days following exposure; too few subjects were vaccinated four to five days post exposure to ascertain the efficacy of vaccine given more than three days after exposure. No included studies reported on adverse events following immunisation.

AUTHORS' CONCLUSIONS

These small trials suggest varicella vaccine administered within three days to children following household contact with a varicella case reduces infection rates and severity of cases. No RCTs for adolescents or adults were identified. However safety was not adequately addressed.

Lack of association between age at varicella vaccination and risk of breakthrough varicella, within the Northern California Kaiser Permanente Medical Care Program

BACKGROUND

Varicella vaccine currently is recommended for children between 12 and 18 months of age. However, rates of breakthrough varicella have been reported to be higher among children vaccinated before 14 or 15 months of age and to increase with time since vaccination.

METHODS

An ongoing study at the Northern California Kaiser Permanente Medical Care Program is evaluating vaccine efficacy in 7585 children vaccinated with Varivax in 1995, when they were between 12 and 23 months of age. Cases of chickenpox are identified by telephone interviews with each child's parent(s) every 6 months. Mean age at varicella onset and mean time from vaccination to onset were calculated on the basis of age, in months, at vaccination. Logistic regression was used to test for trend, and the chi2 test was used to test for differences in rates of breakthrough varicella by age.

RESULTS

Over the first 8 years of the study, a total of 1161 cases of breakthrough varicella were reported, for an average rate of 21.7 cases/1000 person-years. Vaccine effectiveness was 83.6% at year 8. The rate of breakthrough varicella did not change for each additional month of age at vaccination (P = .864), and no difference in the rate of breakthrough varicella was found between children vaccinated at <15 months of age and those vaccinated at > or =15 months of age.

CONCLUSIONS

Our data do not show a difference in vaccine effectiveness with age at vaccination and thus support the current recommendations for initial vaccination between 12 and 18 months of age.

Safety of varicella vaccine after licensure in the United States: experience from reports to the vaccine adverse event reporting system, 1995-2005

Widespread use of varicella vaccine in the United States could enable detection of rare adverse events not identified previously. We reviewed data from 1995 to 2005 from the Vaccine Adverse Event Reporting System, including data from laboratory analyses, to distinguish adverse events associated with wild-type varicella-zoster virus (VZV) versus those associated with vaccine strain. Almost 48 million doses of varicella vaccine were distributed between 1995 and 2005. There were 25,306 adverse events reported (52.7/100,000 doses distributed); 5.0% were classified as serious (2.6/100,000 doses distributed). Adverse events associated with evidence of vaccine-strain VZV included meningitis in patients with concurrent herpes zoster. Patients with genetic predispositions may rarely have disease triggered by receipt of varicella vaccine. Overall, serious adverse events reported after varicella vaccination continue to be rare and must be considered relative to the substantial benefits of varicella vaccination. Ongoing safety surveillance and further studies may shed light on some of the hypothesized associations.

Varicella vaccine effectiveness in the US vaccination program: a review

Varicella vaccine (Varivax, Merck) has been available in the United States since 1995. We reviewed published results of postlicensure studies of vaccine effectiveness. Among 19 studies, 17 reported on the effectiveness of vaccine received before exposure, and 2 reported on effectiveness after exposure. Studies used retrospective and prospective cohort, case-control, and secondary attack rate (household contact) designs. The majority of estimates assessed protection against clinically diagnosed varicella. One dose of varicella vaccine was 84.5% effective (median; range, 44%-100%) in preventing all varicella and 100% effective (mean and median) in preventing severe varicella. When administered after exposure, varicella vaccine was highly effective in preventing or modifying varicella. Although 1 dose of varicella vaccine has provided excellent protection, a higher degree of effectiveness is needed in order to interrupt transmission and to prevent outbreaks in settings with high contact rates. Monitoring the effectiveness of the newly recommended 2-dose childhood vaccine schedule for varicella vaccine is a priority.

The case against universal varicella vaccination

In 1995, the United States became the first country to implement a Universal Varicella Vaccination Program. Several questions remain: Is the varicella (chickenpox) vaccine needed? Is it cost effective as a routine immunization for all susceptible children? Or is it more beneficial for the disease to remain endemic so that adults may receive periodic exogenous exposures (boosts) that help suppress the reactivation of herpes zoster (shingles). In addition, as vaccination coverage becomes widespread, does loss of immunologic boosting cause a decline in vaccine efficacy and result in a reduced period of immunity? Scientific literature regarding safety of the varicella vaccine and its associated cost-benefit analysis have often reported optimistic evaluations based on ideal assumptions. Deleterious outcomes and their associated costs must be included when making a circumspect assessment of the Universal Varicella Vaccination Program.

Safety, tolerability, and immunogenicity of a two-dose regimen of high-titer varicella vaccine in subjects ≥13 years of age

A new manufacturing process, known as process upgrade varicella vaccine (PUVV) was developed for a refrigerated formulation of varicella vaccine and for an investigational zoster vaccine. Safety and tolerability of a two-dose regimen of high-titered (approximately 50,000 PFU) PUVV were compared to a lower-titer formulation (approximately 5400 PFU) of VARIVAX; in 1366 healthy subjects > or =13 years old. Only one vaccine-related clinical serious adverse experience (pruritus; no hospitalization) was reported, in the VARIVAX group. Injection-site adverse experiences following any dose were higher in the PUVV group, 70.0%, than in the VARIVAX group, 56.2%, but generally were mild. Immunogenicity were similar in both groups in seronegative subjects. PUVV was generally well tolerated, and elicited an immune response similar to that induced by the marketed formulation of VARIVAX.

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.

Use of National Health Insurance database to evaluate the impact of public varicella vaccination program on burden of varicella in Taiwan

The aims of this study were to investigate the epidemiology of varicella and evaluate the effect of varicella vaccination on the burden of varicella in Taiwan. The outpatient and hospitalization claims made to the National Health Insurance (NHI) in public and private vaccination areas were compared during 2000-2002. In 2002, the outpatient visit rates for 1- to 5-year-old children in public vaccination areas were 66-78% lower than their counterparts in private vaccination areas. The reduction in outpatient visit rate was the greatest among preschool children. The reductions also occurred in every age group including infants and adults. This study showed significant evidence of vaccine impact with a marked decline in clinical cases in the short term.

Economic evaluation of varicella vaccination in Spain: results from a dynamic model

Varicella is a universal childhood disease in Spain, causing approximately 400,000 cases, 1,500 hospitalizations and 15 deaths every year. The aim of this study is to determine the economic impact of childhood varicella vaccination on the burden of disease and associated costs by using a dynamic model. The analysis is based on the varicella transmission model developed by Halloran and adapted to the Spanish context. Cost data (Euro, 2004) were derived from previous studies and official tariffs. Two vaccination scenarios were analysed: (1) routine vaccination program for children aged 1-2 years, and (2) routine vaccination program for children aged 1-2 years completed by a catch-up program during the first year of vaccine marketing for children aged 2-11 years. The analysis considers that a similar coverage rate to the MMR one would be achieved (97.15%). A societal perspective, including direct and indirect costs, and a health care payor perspective were adopted. A probabilistic sensitivity analysis was performed. A routine vaccination program has a positive impact on varicella-related morbidity: the number of varicella cases is estimated to be reduced by 89%, and 1230 hospitalizations are prevented. From the societal perspective, scenario (1) is cost-saving whether or not indirect costs are considered (-51 and -4%, respectively). From the Health Care System the strategy is cost-effective, with a cost-effectiveness ratio estimated at 3,982 Euro per life-year gained, although it leads to a small increase in the costs. Considering the impact of vaccination on morbidity and costs, a routine childhood vaccination program against varicella is worth while in Spain without taking into account the potential impact on HZ.

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.

[Immunisation against varicella]

Two vaccines against varicella are now being licensed in France, both deriving from the Oka strain. Seroconversion has been obtained in almost 100% of the cases after one dose in toddlers and children, and two doses in adolescents and adults. Efficacy has been mainly established from the US experience, where a universal immunisation programme of children aged > 12 months with a catch-up for susceptible adolescents and adults was begun in 1995. The incidence of varicella has decreased by about 85% over all age groups. The safety of the vaccine is good, and most adverse events are represented by fever, reactions at the injection site and varicella-like rashes. For the time being, France has adopted restrictive recommendations for the use of this vaccine because of uncertainties with respect to the duration of protection, a shift of the disease towards older age and the potential increase of the incidence of herpes-zoster.

The economic value of childhood varicella vaccination in France and Germany

OBJECTIVE

To determine the economic impact of childhood varicella vaccination in France and Germany.

METHODS

A common methodology based on the use of a varicella transmission model was used for the two countries. Cost data (2002 per thousand) were derived from two previous studies. The analysis focused on a routine vaccination program for which three different coverage rates (CRs) were considered (90%, 70%, and 45%). Catch-up strategies were also analyzed. A societal perspective including both direct and indirect costs and a third-party payer perspective were considered (Social Security in France and Sickness Funds in Germany).

RESULTS

A routine vaccination program has a clear positive impact on varicella-related morbidity in both countries. With a 90% CR, the number of varicella-related deaths was reduced by 87% in Germany and by 84% in France. In addition, with a CR of 90%, routine varicella vaccination induces savings in both countries from both societal (Germany 61%, France 60%) and third-party payer perspectives (Germany 51%, France 6.7%). For lower CRs, routine vaccination remains cost saving from a third-party payer perspective in Germany but not in France, where it is nevertheless cost-effective (cost per life-year gained of 6521 per thousand in the base case with a 45% CR).

CONCLUSION

Considering the impact of vaccination on varicella morbidity and costs, a routine varicella vaccination program appears to be cost saving in Germany and France from both a societal and a third-party payer perspective. For France, routine varicella vaccination remains cost-effective in worst cases when a third-party payer perspective is adopted. Catch-up programs provide additional savings.

Consensus: varicella vaccination of healthy children--a challenge for Europe

The seriousness of varicella-zoster virus (VZV) infection as a public health issue is becoming clearer as country-specific epidemiologic and pharmacoeconomic data become available. In Germany, for example, studies have shown that >5.5% of immunologically healthy individuals develop varicella-related complications such as bacterial superinfections, acute neurologic disorders, pneumonia, bronchitis and otitis media; whereas in Italy, 3.5 to 5% of childhood cases of varicella cause complications such as upper respiratory tract and cutaneous infections. Varicella vaccines are now available. These live attenuated Oka strain vaccines have been shown in extensive studies to be highly immunogenic and well-tolerated in immunocompetent and immunocompromised children, with seroconversion rates ranging from 94 to 100% and 53 to 100%, respectively. These vaccines are also highly effective against clinical disease. These considerations led to a reevaluation of varicella vaccination policies. A routine varicella vaccination program targeting healthy children has already been implemented in the US, and data produced are encouraging and valuable. Similar strategies have not yet been adopted across Europe. The European Working Group on Varicella (EuroVar) was formed in 1998 to address the issues surrounding varicella epidemiology in Europe. After a series of meetings, the EuroVar members prepared a consensus statement recommending routine varicella vaccination for all healthy children between 12 and 18 months and to all susceptible children before their 13th birthday, in addition to catch-up vaccination in older children and adults who have no reliable history of varicella and who are at high risk of transmission and exposure. However, such a policy is recommended only if a very high coverage rate can be achieved. This could be reached with a measles-mumps-rubella-varicella combined vaccine.

A post-licensure evaluation of the safety of inactivated hepatitis A vaccine (VAQTA, Merck) in children and adults

BACKGROUND

Hepatitis A is a major cause of epidemic hepatitis in the US. In pre-licensure trials, inactivated hepatitis A vaccine (HAV, VAQTA, Merck) was shown to be generally well-tolerated and effective in inducing immunity to hepatitis A infection in adults and children over 2 years of age. Following the licensure of this vaccine, we began a Phase IV safety evaluation in adults and in children over 2 years of age.

METHODS

Safety was assessed by comparing the rates of diagnoses in clinic, emergency and hospital utilization. From April 1997 to December 1998, rates of diagnoses within 30 days for the clinic and emergency setting and 60 days for hospitalization were compared with unexposed follow-up time in the same individuals both before receipt of vaccine and after the 60 days interval post-vaccination.

RESULTS

There were a total of approximately 2000 comparisons between the risk and "before" or "after" period. Among them, 106 were found to have statistically significant differences in rates (30 elevated, 76 lowered). Among children/adolescents (2-17 year-old), in the hospitalization category, the only statistically significant elevated risk found was "elective procedures", as compared with both "before" and "after" periods. In the outpatient visit category for children and adolescents, elevated risks were found for consultation/general medicine/exam when compared with both "before" and "after" periods, and ganglion and viral warts when compared with either "before" or "after" period. Among adults (> or =18 year-old), in the outpatient visit category, a statistically significant elevated relative risk was seen for diarrhea/gastroenteritis for both "before" and "after" periods. There were additionally 17 diagnostic categories that showed a statistically significantly elevated relative risk compared with either "before" or "after" period. Except for diarrhea/gastroenteritis, the other eight events were elevated only in one comparison (either "before" or "after"). These eight elevated relative risks might be explained by chance resulting from multiple comparison or seasonal variations. There were no serious adverse events judged by the investigator to be associated with HAV.

CONCLUSION

In this large Phase IV evaluation of the safety of HAV, the vaccine appeared to be generally well-tolerated. These data support the continued routine use of HAV for vaccination in children and adults.

Post-marketing evaluation of the short term safety of COMVAX®

We report an evaluation of the short-term safety of a pediatric bivalent combination vaccine containing RECOMBIVAXHB and Liquid PedvaxHIB, COMVAX. Safety was assessed through identification of medical utilization; potential adverse events were identified through computerized clinical databases for deaths, hospitalizations, emergency room visits, and outpatient clinic visits. We calculated relative risks whenever there was at least one diagnosis-specific event in the risk period following vaccination and compared the rates in specific time windows following vaccination with rates at 31-60 days following vaccination and also with rates in a historical cohort of children. A total of 27,802 doses of COMVAX were administered, with 127 separate adverse event codes with statistically significant elevated risks, and 66 codes with significantly decreased risks. Most potentially serious diagnoses appeared in four major categories: "Respiratory Events"; "Gastroenteritis"; "Adverse Effect of Medicinal and Biological Substance, NOS"; and "Fever". There was no consistent pattern to indicate increased risks for serious respiratory or gastrointestinal illness. For fever, most of the findings appeared to be explained by changes in data collection or by concomitant vaccination with M-M-R(-)II. There was an increased risk for fever hospitalizations following shot 1. The total number of children hospitalized with fever was seven out of 12,468 children; all recovered fully. In this study population of 27,802 vaccine recipients, COMVAX appeared to have a favorable safety profile.

Varicella vaccination in Italy : an economic evaluation of different scenarios

AIM

To determine the economic impact (cost-benefit analysis) of childhood varicella vaccination, with the Oka/Merck varicella zoster virus vaccine live (Varivax) in Italy.

METHODS

This analysis is based on an epidemiological model of varicella zoster virus (VZV) dynamics adapted to the Italian situation. Cost data (Euro, 2002 values) were collected through a literature review. Several vaccination scenarios were analysed: (i) routine vaccination programme for children aged 1-2 years with different levels of vaccination coverage (90%, 70% and 45%) without any catch-up programme; (ii) routine vaccination programme for children aged 1-2 years with different levels of vaccination coverage (90%, 70% and 45%) completed by a catch-up programme for 6-year-old children over the first 5 years of vaccine marketing; and (iii) routine vaccination programme for children aged 1-2 years with different levels of vaccination coverage (90%, 70% and 45%) completed by a catch-up programme during the first year of vaccine marketing for children aged 2-11 years.

PERSPECTIVES

A societal perspective, including both direct and indirect costs, and a health-system perspective, limited to costs supported by Italian Health Authorities, were considered.

RESULTS

A routine vaccination programme has a clearly positive impact on chickenpox morbidity. Respectively, 68% and 57% of chickenpox-related hospitalisations and deaths could be prevented with a 90% coverage rate. With vaccination costs being more than offset by a reduction in chickenpox treatment costs in the base case, such a programme could also induce savings from both a societal and a health-system perspective (40% and 12% savings, respectively for a 90% coverage rate). A lower coverage rate reduces cost savings, but there is still a 9% decrease in overall societal costs for a 45% coverage rate. Although the reduction in total societal costs was robust to the sensitivity analyses performed, a slight uncertainty remains regarding cost reduction from a health-system perspective. However, in this latter perspective, even in the worst-case scenario of the sensitivity analysis, routine vaccination programmes may be cost effective, the worst-case scenario for cost parameters leading to cost per life-year gained of Euro2853. Catch-up programmes combined with routine vaccination should lead to further cost reductions from a societal perspective: 15% for a massive catch-up during the first year of vaccine marketing compared with toddlers' vaccination alone, and 11% for a catch-up focused on 6-year-old children for a period of 5 years. However, the impact of catch-up programmes on the costs from an Italian health-system perspective remains close to zero (+/-1%).

CONCLUSION

This model suggests, with its underlying assumptions and data, that routine ZVZ vaccination may be cost saving from both a societal and a health system perspective in the base case. In the worst-case scenario of the sensitivity analysis, vaccination remains cost effective.

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.

Varicella vaccination: impact of vaccine efficacy on the epidemiology of VZV

In 1995, varicella vaccination was introduced into the infant immunization schedule of the United States. Currently, many other countries are considering mass varicella vaccination. Mass vaccination has two dangers: it could increase the number of varicella cases in adults, where severity is greater, and increase cases of zoster. A deterministic, realistic, age-structured model (RAS) was built to study these concerns. Model parameter estimates were derived from a review of the literature and surveillance data from England and Wales. Different vaccine efficacy scenarios, vaccine coverages, and vaccination strategies were investigated. The model predicts that, although an upward shift in the age at infection occurs, the overall morbidity due to varicella is likely to decrease following mass infant vaccination. On the other hand, cases of zoster may significantly increase in the first 50 years following vaccination. The model predicts that, in a population similar to England and Wales (50 m people), varicella vaccination with 90% coverage would prevent 0.6 m inpatient days due to varicella but would generate an extra 1.1 m inpatient days due to zoster over the first 65 years. Thus, under base-case model assumptions, the gain in reduction of varicella morbidity from infant vaccination is offset in the short-term by the increases in zoster morbidity (using inpatient days as a proxy). Paradoxically, less effective vaccines or vaccine programmes can be more effective in reducing overall morbidity (varicella + zoster) by allowing the virus to circulate more, which produces a smaller shift in the age at infection and a smaller increase in zoster cases.

Canada's first universal varicella immunization program: Lessons from Prince Edward Island

A live attenuated varicella vaccine was licensed in Canada in December 1998. The first universal varicella immunization program in Canada was initiated in Prince Edward Island in 2000. Students in grades one to six without a history of varicella were offered the vaccine, administered by Public Health Nurses, in school clinics during February and March 2000. The acceptance rate ranged from 29.1% of all grade one students to 9.8% of all grade six students; overall, 18.8% of students received the vaccine. A universal program for children 12 months of age was introduced on April 1, 2000 and catch-up clinics for those between 12 months of age and those in grade one were introduced in June 2000. Repeated media announcements and the cooperation of staff in schools and daycare facilities assisted in informing parents about the availability of the vaccine. Vaccine-associated adverse events have been uncommon and the vaccine has been well accepted.