Childhood vaccination against varicella: persistence of antibody, duration of protection, and vaccine efficacy

Loss of humeral immunity in childhood cancer survivors not having undergone hematopoietic stem cell transplantation

BACKGROUND

Data are limited and conflicting regarding loss of immunity in childhood cancer survivors who did not undergo hematopoietic stem cell transplantation. The purpose of this retrospective, single center study is to provide further data to help build unifying revaccination guidelines post-chemotherapy in childhood cancer survivors not having undergone hematopoietic stem cell transplantation.

METHODS

This retrospective study included 28 childhood cancer survivors, 14 males and 14 females, whose treatment consisted of at least 3 months of chemotherapy and with confirmation of completing their primary vaccination series prior to therapy. The rate of vaccine titer seropositivity for cancer survivors was compared with the expected general population, based on long-term studies of anti-body persistence.

RESULTS

Decreased seropositivity for measles, mumps, rubella, varicella, tetanus, and hepatitis B was found in patients across all categories of malignancy compared with the general population. However, tetanus was not statistically significant. Results were more pronounced for those with hematological malignancies.

CONCLUSIONS

This study indicates that pediatric cancer survivors, especially those with hematological malignancies, may have greater loss of protective antibodies from primary vaccinations. Further studies are needed to provide guidelines for revaccination of both hematologic malignancies and solid tumor childhood cancer survivors who did not undergo hematopoietic stem cell transplantation.

Long-term study showed that vaccination protected paediatric renal transplant recipients from life-threatening varicella zoster virus

AIM

Renal transplant patients are particularly susceptible to highly contagious diseases due to their reduced immunity. We studied transplant recipients to gauge their varicella zoster virus (VZV) serology status over time and the outcome of any VZV infections.

METHOD

This retrospective study comprised 85 children who underwent renal transplants in Gothenburg, Sweden, from 1986 to 2014, at a mean age of eight (1-18) years. The children's medical records were reviewed and 47 had the VZV infection pre-transplant and 38 had been vaccinated pre-transplant. Clinical outcomes were available for 85 children and serology results for 72.

RESULTS

At transplantation, the VZV seropositivity rate was 50% in the vaccination group and 94% in the infection group and the antibody titres were significantly lower in the vaccination group (p = 0.031). During the median follow-up period of five years post-transplant, 28% of the vaccinated children and 97% of the infection group remained seropositive and the varicella infection affected eight children: one in the infection group and seven in the vaccination group. The herpes zoster was observed in two children in the infection group.

CONCLUSION

This study demonstrated that VZV vaccination protected from symptomatic infections to a lesser extent than natural infection, but provided effective protection from life-threatening disease.

Epidemiology of Breakthrough Varicella after the Implementation of a Universal Varicella Vaccination Program in Taiwan, 2004-2014

National one-dose varicella vaccination at 12 months of age was implemented in Taiwan since 2004.Our study aimed to evaluate breakthrough varicella (BV) in post-vaccine era and its associated risk factors. We retrospectively identified children vaccinated against varicella between 12-23 months of age during 2004-2008. Their vaccination information was extracted from the national vaccination registry system and linked to the 2004-2014 National Health Insurance database. BV was defined as a diagnosis of varicella (ICD-9-CM codes 052 and 052.0-052.9) beyond 42 days post-vaccination. Multiple Cox regression model was used to identify risk factors for BV. Among 932,874 enrolled vaccinees, 26,446 (2.8%) had BV and 219 (0.024%) required hospitalization over the study period. Varicella incidence declined from 4.71 per 1000 person-year (PY) in 2004 to 0.81/1000 PY in 2014. BV incidence decreased from 3.90/1000 PY at first year to 1.94/1000 PY at 11th year after vaccination. Females had a lower risk for BV than males (hazard ratio [HR] 0.85, 95% CI, 0.83-0.87); Varivax^® recipients had a lower risk for BV than Varilrix^® recipients (HR 0.75, 95% CI, 0.72-0.78). Our study showed the incidence of varicella, BV and varicella-related hospitalizations in Taiwan were kept low in post-vaccine era.

Single-dose varicella vaccine effectiveness in Brazil: A case-control study

BACKGROUND

Varicella vaccine was introduced into the Brazilian Immunization Program in October 2013, as a single-dose schedule administered at 15 months of age. Its effectiveness had not yet been assessed in the country.

METHODS

A matched case-control study was carried out in São Paulo and Goiânia (Southeast and Midwest regions, respectively), Brazil. Suspected cases, were identified through a prospective surveillance established in the study sites. All cases had specimens from skin lesion collected for molecular laboratory testing. Cases were confirmed by either clinical or PCR of skin lesions and classified as mild, moderate, and severe disease. Two neighborhood controls were selected for each case. Cases and controls were aged 15-32 months and interviewed at home. Evidence of prior vaccination was obtained from vaccination cards. Univariate and multivariate logistic regression models were used, and odds ratio and its respective 95% confidence intervals were estimated. Vaccine effectiveness was estimated by comparing de odds of having received varicella vaccine among cases and controls.

RESULTS

A total of 168 cases and 301 controls were enrolled. Moderate and severe illness, was found in 33.3% and 9.9% of the cases. Effectiveness of a single dose varicella vaccine was 86% (95%CI 72-92%) against disease of any severity and 93% (95%CI 82-97%) against moderate and severe disease. Out of 168 cases, 81.8% had positive PCR results for wild-type strains, and 22.0% were breakthrough varicella cases. Breakthrough cases were milder compared to non-breakthrough cases (p < .001).

CONCLUSIONS

Effectiveness of single dose varicella vaccine in Brazil is comparable to that in other countries where breakthrough varicella cases have also been found to occur. The goal of the varicella vaccination program, along with disease burden and affordability should be taken into consideration when considering the adoption of a second dose of varicella vaccine into national immunization programs.

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.

Protection against varicella with two doses of combined measles-mumps-rubella-varicella vaccine versus one dose of monovalent varicella vaccine: a multicentre, observer-blind, randomised, controlled trial

BACKGROUND

Rates of varicella have decreased substantially in countries implementing routine varicella vaccination. Immunisation is possible with monovalent varicella vaccine or a combined measles-mumps-rubella-varicella vaccine (MMRV). We assessed protection against varicella in naive children administered one dose of varicella vaccine or two doses of MMRV.

METHODS

This study was done in ten European countries with endemic varicella. Healthy children aged 12-22 months were randomised (3:3:1 ratio, by computer-generated randomisation list, with block size seven) to receive 42 days apart (1) two doses of MMRV (MMRV group), or (2) MMR at dose one and monovalent varicella vaccine at dose two (MMR+V group), or (3) two doses of MMR (MMR group; control). Participants and their parents or guardians, individuals involved in assessment of any outcome, and sponsor staff involved in review or analysis of data were masked to treatment assignment. The primary efficacy endpoint was occurrence of confirmed varicella (by detection of varicella zoster virus DNA or epidemiological link) from 42 days after the second vaccine dose to the end of the first phase of the trial. Cases were graded for severity. Efficacy analyses were per protocol. Safety analyses included all participants who received at least one vaccine dose. This trial is registered with ClinicalTrials.gov, number NCT00226499.

FINDINGS

Between Sept 1, 2005, and May 10, 2006, 5803 children (mean age 14·2 months, SD 2·5) were vaccinated. In the efficacy cohort of 5285 children, the mean duration of follow-up in the MMRV group was 36 months (SD 8·8), in the MMR+V group was 36 months (8·5) and in the MMR group was 35 months (8·9). Varicella cases were confirmed for 37 participants in the MMRV group (two moderate to severe), 243 in the MMR+V group, and 201 in the MMR group. Second cases occurred for three participants (all in the MMR+V group). Varicella cases were moderate to severe for two participants in the MMRV group, 37 in the MMR+V group (one being a second case that followed a mild first case); and 117 in the MMR group. Efficacy of two-dose MMRV against all varicella was 94·9% (97·5% CI 92·4-96·6), and against moderate to severe varicella was 99·5% (97·5-99·9). Efficacy of one-dose varicella vaccine against all varicella was 65·4% (57·2-72·1), and against moderate to severe varicella (post hoc) was 90·7% (85·9-93·9). The most common adverse event in all groups was injection-site redness (up to 25% of participants). Within 15 days after dose one, 57·4% (95% CI 53·9-60·9) of participants in the MMRV group reported fever of 38°C or more, by contrast with 44·5% (41·0-48·1) with MMR+V, and 39·8% (33·8-46·1) with MMR. Eight serious adverse events were deemed related to vaccination (three MMRV, four MMR+V, one MMR). All resolved within the study period.

INTERPRETATION

These results support the implementation of two-dose varicella vaccination on a short course, to ensure optimum protection from all forms of varicella disease.

FUNDING

GlaxoSmithKline Vaccines.

Varicella zoster virus: vaccination and implications in children with renal failure

The varicella zoster virus is associated with significant disease in those with chronic kidney disease, both pre- and postrenal transplantation. With the advent of the varicella vaccine, the opportunity to prevent significant morbidity and mortality exists. Despite the secondary immune defects associated with renal failure, the varicella vaccine has been demonstrated to be immunogenic, safe and efficacious in pediatric patients with kidney disease.

Economic evaluation of vaccines: specificities and future challenges illustrated by recent European examples

This study reviews the current challenges in the economic evaluation of vaccines with a focus on European countries. In particular, the type of clinical evidence generally available, the impact of discounting for time preference and the use of modeling to derive valid cost-effectiveness assessments are considered. First, the characteristics of evidence for vaccines are discussed, as well as potential difficulties faced when using evidence-based medicine applied to curative drugs to interpret vaccine evidence. Then, discounting is considered and specific examples illustrating issues with different types of discounting are described, taking HPV as the example. Finally, the need for sometimes complex dynamic models for vaccines is explored, and specific types of models are reviewed, keeping into consideration the adage "complex when needed, straightforward if allowed."

Primary versus secondary failure after varicella vaccination: implications for interval between 2 doses

BACKGROUND

Two-dose varicella vaccination is recommended for optimal control of varicella in populations with high (>90%) 1-dose coverage. Optimal timing of the second dose may depend on whether breakthrough varicella results from primary vaccine failure (no protective immunity after vaccination) or secondary vaccine failure (waning protective immunity).

METHODS

Published literature (1995 to 2012) on vaccine failure after varicella vaccination cited in PubMed and other online sources was reviewed.

RESULTS

Nineteen publications detailed 21 varicella outbreaks with breakthrough varicella rates ranging from 0% to 42%; the publications showed no consistent trend between breakthrough varicella rate and time since vaccination.

CONCLUSIONS

Literature to date indicates a relatively high rate of primary vaccine failure and limited evidence of secondary vaccine failure among 1-dose varicella vaccine recipients, suggesting that a short interval between 2 doses might be preferable in countries considering implementation of universal varicella vaccination to reduce breakthrough varicella. However, any potential disruption to well-established vaccination schedules should be considered.

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.

VZV T cell-mediated immunity

Primary varicella-zoster virus (VZV) infection (varicella) induces VZV-specific antibody and VZV-specific T cell-mediated immunity. T cell-mediated immunity, which is detected within 1-2 weeks after appearance of rash, and consists of both CD4 and CD8 effector and memory T cells, is essential for recovery from varicella. Administration of a varicella vaccine also generates VZV-specific humoral and cellular immune responses. The memory cell responses that develop during varicella or after vaccination contribute to protection following re-exposure to VZV. These responses are subsequently boosted either by endogenous re-exposure (silent reactivation of latent virus) or exogenous re-exposure (environmental). VZV-specific T cell-mediated immunity is also necessary to maintain latent VZV in a subclinical state in sensory ganglia. When these responses decline, as occurs with aging or iatrogenic immune suppression, reactivation of VZV leads to herpes zoster. Similarly, the magnitude of these responses early after the onset of herpes zoster correlates with the extent of zoster-associated pain. These essential immune responses are boosted by the VZV vaccine developed to prevent herpes zoster.

The effectiveness of varicella vaccine in China

BACKGROUND

The attenuated live varicella vaccine had been shown to be effective in preventing varicella and reducing the disease burden in the United States. However, little work has been done on investigating vaccine effectiveness in China where 3 varicella vaccines are available. Although the vaccines contain the same strain of virus, the vaccines licensed in China were from manufacturers different from the one licensed in the United States. We conducted a matched case-control study to assess the effectiveness of the 3 varicella vaccines in use in China.

METHODS

In 2005, we enrolled 1000 cases from Guangzhou, China and 1000 controls matched by age and place of residence. The cases were children clinically diagnosed with acute onset of a diffuse maculopapulovesicular rash without other apparent cause. We interviewed the legal guardians of the participants for demographic information and disease history after obtaining informed consent. We collected information on vaccination status from electronic vaccination records.

RESULTS

The 3 varicella vaccines in China (Varilrix from GlaxoSmithKline, Changchun and Shanghai from Changchun and Shanghai Institutes of Biologic Products, respectively) had similar effectiveness: Varilrix 86.4% (95% confidence interval [CI]: 72.6, 93.2), Changchun 79.5% (95% CI: 58.1, 90.0), and Shanghai 92.6% (95% CI: 68.9, 98.2). Vaccine effectiveness was higher during the first year after vaccination than during the subsequent 5 years, but the differences did not reach statistical significance.

CONCLUSIONS

The varicella vaccines in China are highly effective in preventing clinical varicella. Further studies on laboratory-confirmed cases are needed to verify the change of vaccine-induced immunity over time.

Modelling the impact of one-dose vs. two-dose vaccination regimens on the epidemiology of varicella zoster virus in Australia

We examined the impact of one-dose vs. two-dose vaccination strategies on the epidemiology of varicella zoster virus (VZV) in Australia, using a mathematical model. Strategies were assessed in terms of varicella (natural and breakthrough) and zoster incidence, morbidity, average age of infection and vaccine effectiveness (VE). Our modelling results suggest that compared to a one-dose vaccination strategy (Australia's current vaccination schedule), a two-dose strategy is expected to not only produce less natural varicella cases (5% vs. 13% of pre-vaccination state, respectively) but also considerably fewer breakthrough varicella cases (only 11·4% of one-dose strategy). Therefore a two-dose infant vaccination programme would be a better long-term strategy for Australia.

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.

Laboratory diagnosis and characteristics of breakthrough varicella in children

The atypical features of varicella in vaccinated persons (breakthrough varicella [BTV]) present diagnostic challenges. We examined varicella-zoster virus (VZV) polymerase chain reaction (PCR) and immunoglobulin (Ig) M and IgG serologic test results for confirming BTV cases. Among 33 vaccinated children with varicella-like rash, we identified wild-type VZV in 58% overall and in 76% of those with adequate tissue specimens; no vaccine-type virus was found. Of the 12 subjects with PCR-confirmed BTV and acute-phase serum samples, 9 had detectable IgM, and all had highly elevated acute-phase IgG titers. Six subjects with negative PCR results had lower IgG titers and negative IgM results. Although PCR is the preferred method for laboratory confirmation of BTV, a positive serum varicella IgM test result should also be considered to be diagnostic in a suspected BTV case; however, a negative IgM test result cannot be used to rule out the diagnosis. The value of highly elevated IgG titers needs further evaluation. Larger studies are needed to confirm these results.

Cost of varicella-related hospitalisations in an Italian paediatric hospital: comparison with possible vaccination expenses

OBJECTIVE

The aims of the study were to evaluate the economic burden of hospitalisations due to varicella in an Italian paediatric hospital during a 1-year period and to compare the data with potential expenses projected for a varicella mass vaccination programme.

RESEARCH DESIGN AND METHODS

An observational, retrospective, cohort study was designed to measure hospital admission costs in a cohort of paediatric patients with varicella in a 12-month period. A cost comparison with a vaccination programme planned to prevent varicella in a whole birth cohort was performed. All children 0-16 years referred to the Anna Meyer Children's Hospital (AMCH) were considered. Since AMCH is a tertiary-level hospital and accept patients from other Italian regions, in order to avoid overestimation of hospitalisation expenses, all analyses pertaining to both vaccination and hospitalisation costs were uniquely calculated on the basis of the cohort of residents in the district of Florence.

RESULTS

A total of 279 children were examined in the emergency department for varicella; 47/279 (16.8%) were sent to the inpatient clinic. The highest rate of hospitalisation (85.1%) was found in children < 4 years of age, and the largest number of complications (87.2%) occurred in previously healthy children. Mean length of hospitalisation (5.7 +/- 0.6 days) was similar to that reported in other western countries.

CONCLUSION

Excluding any indirect cost, permanent sequelae and serious outcomes such as death, hospital expenses (corresponding to euro239 654 in a 1-year period), would account for around 80% of total expenses for vaccinating an entire birth cohort (euro310353).

Review of the Varilrix varicella vaccine

Varicella zoster virus causes an acute infection that affects most children globally, but the age of infection can be greater in residents of tropical areas. It has generally been considered a mild disease, although there are accumulating data to show that it can cause significant morbidity and mortality in immunocompetent as well as immunocompromised children and adults. Oka-strain live attenuated varicella vaccines were developed in the 1970s. Varilrix developed by GlaxoSmithKline Biologicals (Rixensart, Belgium), is one of the vaccines produced and marketed in over 80 countries. Similar to the other Oka-strain vaccines, Varilrix is safe, immunogenic and efficacious in both immunocompromised and immunocompetent children and adults.

The optimization and validation of the glycoprotein ELISA assay for quantitative varicella-zoster virus (VZV) antibody detection

Varicella is a highly contagious viral disease found throughout the world. A live-attenuated Varicella-Zoster virus (VZV) vaccine (Oka/Merck strain), VARIVAXtrade mark, was licensed in the United States (US) in 1995 and was made a part of the US recommended childhood vaccination schedule in 1996. The immune response to VZV-containing vaccines has been measured using an enzyme-linked immunosorbent assay (ELISA) to detect antibodies to glycoproteins from VZV. A correlate for protective immunity has been established between anti-VZV glycoprotein antibody levels and protection against breakthrough varicella in children, and this correlate is used as the primary immunogenicity endpoint in clinical trials with VZV-containing vaccines. The performance of the "first generation" validated version of the assay was recently reevaluated in order to identify areas for improvement. Specific format and reagent changes were implemented, with the goal of improving assay consistency by maintaining tighter control over assay processes and reagents. An extensive validation of the "second generation" gpELISA was undertaken in order to characterize the updated assay. In this article, we describe the gpELISA method, detail the procedures used to evaluate assay performance, and present the operating characteristics of the second generation gpELISA.

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.

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.

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.

Is Europe ready to embrace a policy of universal varicella vaccination?

For the first time, a live attenuated varicella vaccine with an indication for universal vaccination is licensed in all EU countries. It is now time to consider whether in Europe there should be widespread vaccination against varicella to prevent this common and highly infectious disease. Increasing numbers of countries are adopting vaccination programmes against the disease. In those countries where a routine vaccination policy has been adopted, the success of the vaccine has been significant. The USA, which prior to the launch of a universal vaccination programme in 1995 had 4 million cases of varicella per year, has seen a dramatic reduction in varicella morbidity and mortality rates. A universal varicella vaccination policy is an option that needs to be considered for Europe not only in medical terms but also because it would be socially and economically appropriate.

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.

Immunisation in the current management of cystic fibrosis patients

Although no special recommendations exist, clearly patients with cystic fibrosis (CF) can benefit from immunisation. We reviewed the literature regarding vaccination in CF and other chronic diseases. CF subjects should follow national immunisation programmes without delay to obtain optimal vaccination coverage. Indeed they may escape normal programmes due to frequent hospital admissions and school absenteeism and may be more at risk to get "vaccine-controlled" diseases at any age. There is no uniform European immunisation schedule for basic infant and childhood vaccines or for vaccines against hepatitis A (HAV) and B (HBV), varicella (VZ) and booster vaccinations. HAV and HBV vaccination is appropriate in CF as recommended in general for patients with chronic liver disease (CLD). Varicella (VZ) vaccination is not recommended in all European countries. There are no recent data about possible worsening of pulmonary status following VZ in CF, but it is known to cause pulmonary damage in non-CF adults and to be potentially fatal post transplantation and during steroid treatment. Therefore it is recommended at least for seronegative adolescents and transplant candidates. Influenza vaccine is recommended annually for CF patients aged > or =6 months. Pneumococcal vaccine is generally indicated for CF patients. RSV infection might play a role in the initial Pseudomonas colonization and the decline in pulmonary function. However no RSV vaccine is available at present. There are no recommendations for palivizumab in CF as an alternative but expensive prophylaxis. Anti-bacterial vaccinations protecting directly against Pseudomonas aeruginosa colonisation are promising for the future, potential candidates are currently being assessed in phase III clinical trials. More studies are needed to complete recommendations especially for CF adults and transplant candidates.

Importance of catch-up vaccination: experience from a varicella outbreak, Maine, 2002-2003

OBJECTIVE

During December 2002 to January 2003, a varicella outbreak occurred in an elementary school in Maine. Just 1 month before detecting the outbreak, Maine implemented varicella vaccine requirements for child care but did not require vaccination for school entry. We investigated this outbreak to examine reasons for its occurrence, including vaccine failure.

METHODS

A self-administered questionnaire was sent to all students' parents to determine student disease status, medical conditions, and vaccination status, which was further confirmed by review of medical records. Parental reporting of chickenpox/varicella that occurred since September 1, 2002, in a student who attended the school was used to define a case. Parents of cases were interviewed by telephone about disease characteristics. Disease severity was classified on the basis of the number of skin lesions and the occurrence of complications. Vaccine effectiveness was calculated by comparing varicella attack rates for any disease, for moderate to severe disease, and for severe disease among vaccinated and unvaccinated students.

RESULTS

We obtained complete information for 296 (81%) of 364 students. Varicella vaccine coverage was 74% overall and decreased by grade, from 90% in kindergarten to 60% in third grade. Attack rates increased significantly from 14% in kindergarten to 37% in third grade. Of the 53 varicella cases, 36 (68%) were unvaccinated, 12 (22%) were vaccinated, and 5 (10%) had previous disease history. Vaccine effectiveness was 89% (95% confidence interval [CI]: 79-94%) against disease of any severity, 96% (95% CI: 88-99%) against moderate to severe disease, and 100% (95% CI: undefined) against severe disease. Twenty-two percent of unvaccinated students had severe disease and 1 was hospitalized for a skin infection, whereas none of the vaccinated cases reported severe disease.

CONCLUSION

This outbreak was attributable primarily to failure to vaccinate, especially among children in grades 1 through 3. Catch-up vaccination of susceptible older children and adolescents is especially important to prevent accumulation of susceptibility in these groups, in which the natural disease is more severe. School entry requirements will contribute to a more rapid implementation of the existing recommendations for vaccination.

Efficacy of postexposure immunization with live attenuated varicella vaccine in the household setting—a pilot study

The aim of the present study was to examine the efficacy of postexposure vaccination with Varilrix in the household setting. A randomized, double-blind, placebo-controlled design was used. Twenty-two children received the varicella vaccine and 20, a placebo. The relative risk of developing varicella with a placebo compared with the vaccine was 1.1 (95% confidence interval 0.55-2.21). The risk of developing moderate to severe disease was eight times greater in the placebo group (RR=8), indicating an 80% protective effect against moderate/severe disease. The varicella vaccine Varilrix may not be effective in preventing varicella when administered after household exposure, although it is highly effective in ameliorating the disease in those who acquire it under these circumstances.

Declining incidence of chickenpox in the absence of universal childhood immunisation

OBJECTIVE

To examine the epidemiology of chickenpox in Wales from 1986 to 2001.

DESIGN

Descriptive analysis of chickenpox consultations reported by the Welsh general practice sentinel surveillance scheme for infectious diseases, compared with annual shingles consultation rates from the same scheme to exclude reporting fatigue and data from a general practice morbidity database to validate results.

SETTING

A total of 226,884 patients registered with one of 30 volunteer general practices participating in the sentinel surveillance scheme.

MAIN OUTCOME MEASURES

Age standardised and age specific incidence of chickenpox.

RESULTS

Crude and age standardised consultation rates for chickenpox declined from 1986 to 2001, with loss of epidemic cycling. Rates remained stable in 0-4 year olds but declined in all older age groups, particularly those aged 5-14 years. Shingles consultation rates remained constant over the same period. Data from the morbidity database displayed similar trends.

CONCLUSION

General practitioner consultation rates for chickenpox are declining in Wales except in pre-school children. These findings are unlikely to be a reporting artefact but may be explained either by an overall decline in transmission or increased social mixing in those under 5 years old, through formal child care and earlier school entry, and associated increasing rates of mild or subclinical infection in this age group. Further investigation, particularly by serological surveillance, is necessary before universal varicella immunisation can be considered in the UK.

A review of the varicella vaccine in immunocompromised individuals

BACKGROUND

Individuals with underlying cell-mediated immunodeficiency disorders are at high risk of developing severe, life-threatening illness associated with varicella-zoster virus infection. A live-attenuated varicella vaccine is recommended for routine childhood immunisation in some countries. In healthy children, the vaccine is efficacious and safe but because immunocompromised individuals may be unable to limit replication of live-attenuated vaccine viruses, the varicella vaccine is not recommended for them and there are few exceptions.

OBJECTIVES

The purpose of this paper is to review the published studies addressing the use of the varicella vaccine in people with cell-mediated immunodeficiency disorders.

METHODS

A computerised search on the PubMed database was used to collect the relevant papers published up to March 2003.

RESULTS

The varicella vaccine has been extensively studied in susceptible children with acute lymphoblastic leukaemia in remission, but studies involving individuals with other immunodeficiency disorders are scarce. Some of the current recommendations are based on very few and small studies with short follow-up. Immunocompromised individuals should be given the varicella vaccine only with complete knowledge of their clinical and immunological conditions and after considering the risks of natural infection and vaccination.

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.

Use of a computerized database to study the effectiveness of an attenuated varicella vaccine

BACKGROUND

The varicella vaccine Varilrix (GlaxoSmithKline) was introduced in Israel in June 2000 as an optional vaccination for children.

METHODS

We used the database of a single health maintenance organization that serves 25% of the population in Israel to assess the effectiveness of the vaccine retrospectively. Incidence and complications of varicella were derived from the database from January 1, 1998 until December 31, 2002.

RESULTS

Since licensure >30000 individuals younger than 10 years in this health maintenance organization have been immunized with the vaccine. Annual incidence of disease per 1000 in the study population was 86.6 in 1998, 74.6 in 1999, 74.0 in 2000, 37.1 in 2001 and 44.6 in 2002. This declining trend in incidence of disease was statistically significant. Complications of varicella occurred in approximately 1% of patients throughout the 5-year study period, but there was a parallel decline in the number of patients with complications corresponding to the decline in disease incidence. Vaccine effectiveness for prevention of clinical disease in this population was 92% (95% confidence interval, 91.0 to 92.7). There were varying rates of utilization within communities of varied socioeconomic class, so that in the higher socioeconomic class there was an increased utilization and a corresponding decrease of attack rate; whereas in communities where there were lower utilization rates, corresponding increased numbers of varicella cases were seen.

CONCLUSION

This database enables long term follow-up of the effectiveness of this vaccine in a large population.

Ten year follow-up of healthy children who received one or two injections of varicella vaccine

BACKGROUND

The rate of varicella and persistence of varicella antibody after a one dose vs. a two dose regimen of varicella virus vaccine live Oka/Merck (VARIVAX; Merck & Co., Inc., West Point, PA) in approximately 2000 children were compared during a 9- to 10-year follow-up period.

METHODS

Children 12 months to 12 years of age with a negative history of varicella were randomized in late 1991 to early 1993 to receive either one or two injections of varicella vaccine given 3 months apart. Subjects were actively followed for varicella, any varicella-like illness or zoster and any exposures to varicella or zoster on a yearly basis for 10 years after vaccination. Persistence of varicella antibody was measured yearly for 9 years.

RESULTS

Most cases of varicella reported in recipients of one or two injections of vaccine were mild. The risk of developing varicella >42 days postvaccination during the 10-year observation period was 3.3-fold lower (P < 0.001) in children who received two injections than in those who received one injection (2.2% vs. 7.3%, respectively). The estimated vaccine efficacy for the 10-year observation period was 94.4% for one injection and 98.3% for two injections (P < 0.001). Measurable serum antibody persisted for 9 years in all subjects.

CONCLUSIONS

Administration of either one or two injections of varicella vaccine to healthy children results in long term protection against most varicella disease. The two dose regimen was significantly more effective than a single injection.

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.

Controversies in chicken-pox immunization

Chicken-pox is one more newer vaccine in our armamentarium against infectious diseases. Due to its extremely contagious nature, varicella is experienced by almost every child or young adult in the world. Each year from 1990 to 1994, prior to availability of varicella vaccine, about 4 million cases of varicella occurred in the United States. Of these cases approximately 10,000 required hospitalization and 100 died. Although varicella is not commonly perceived as an important public health problem, the socioeconomic consequences in industrialized countries of a disease that affects practically every child and causes the carrier absence from work should not be underestimated. The varicella vaccines available in the market are safe and effective. A recent cost-benefit analysis in USA showed that routine chicken-pox vaccination is likely to save five times the investment. Even when only direct costs were considered, benefits almost balanced the costs. At present similar studies from developing countries are not available. The public health impact of varicella and zoster may be increasing in regions with high endemic rates of HIV infection. Varicella vaccine may be used either at an individual level to protect susceptible adolescents and adults, or at a population level, to cover all children as part of a national immunization programme. Vaccination of adolescents and adults will protect at-risk individuals, but will not have a significant impact on the epidemiology of the disease on a population basis. On the other hand, extensive use as a routine vaccine in children will have a significant impact on the epidemiology of the disease. If sustained high coverage can be achieved, the disease may virtually disappear. If only partial coverage can be obtained, the epidemiology may shift, leading to an increase in the number of cases in older children and adults. Hence, routine childhood varicella immunization programmes should emphasize high, sustained coverage. At present, this vaccine will have a lower priority in the National Immunization Schedule that does not have MMR and typhoid, which have a greater socioeconomic impact. Hence, at the present time WHO does not recommend the inclusion of varicella vaccination into the routine immunization programmes of developing countries.

Vaccines for viral diseases with dermatologic manifestations

Vaccines against infectious diseases have been available since the 1800s, when an immunization strategy against smallpox developed by Jenner gained wide acceptance. Until recently, the only vaccination strategies available involved the use of protein-based, whole killed, and attenuated live virus vaccines. These strategies have led to the development of effective vaccines against a variety of diseases with primary or prominent cutaneous manifestations. Effective and safe vaccines now used worldwide include those directed against measles and rubella (now commonly used together with a mumps vaccine as the trivalent MMR), chickenpox, and hepatitis B. The eradication of naturally occurring smallpox remains one of the greatest successes in the history of modern medicine, but stockpiles of live smallpox exist in the United States and Russia. Renewed interest in the smallpox vaccine reflects concerns about a possible bioterrorist threat using this virus. Yellow fever is a hemorrhagic virus endemic to tropical areas of South America and Africa. An effective vaccine for this virus has existed since 1937, and it is used widely in endemic areas of South America, and to a lesser extent in Africa. This vaccine is recommended once every 10 years for people who are traveling to endemic areas. Advances in immunology have led to a greater understanding of immune system function in viral diseases. Progress in genetics and molecular biology has allowed researchers to design vaccines with novel mechanisms of action (eg, DNA, vector, and VLP vaccines). Vaccines have also been designed to specifically target particular viral components, allowing for stimulation of various arms of the immune system as desired. Ongoing research shows promise in prophylactic and therapeutic vaccination for viral infections with cutaneous manifestations. Further studies are necessary before vaccines for HSV, HPV, and HIV become commercially available.

Use of statistical models for evaluating antibody response as a correlate of protection against varicella

In vaccine clinical trials, humoral antibody responses are often used to measure the effect of a vaccine because they correlate with a vaccine's protective efficacy against the target disease. While the concept of a correlate of protection usually refers to establishing a protective level of antibody titre, identifying a clear-cut value is often impossible because vaccine efficacy is not related solely to the antibody titre. We propose examining the relationship between disease protection and the whole distribution of antibody responses rather than a single cut-off level. In particular, we use failure-time models to estimate the relationship between long-term disease breakthroughs and primary antibody responses after vaccination. We apply these models to show that the varicella antibody response measured by glycoprotein enzyme-linked immunosorbent assay 6 weeks after vaccination strongly correlate with protection against varicella (chickenpox); we used 7-year follow-up data from children who received one dose of a live attenuated varicella (Oka/Merck) vaccine. In addition, we explore the potential use of these models to predict long-term disease breakthrough rates and to estimate the predicted vaccine efficacy of a similar varicella vaccine made with a modified manufacturing process.

Varicella-related hospitalizations in the vaccine era

BACKGROUND AND AIM

Varicella is normally a self-limited disease of childhood that does not require hospitalization. In the prevaccine era varicella caused >9000 hospitalizations per year. To determine whether the varicella vaccine, licensed in 1995, has decreased hospitalizations because of varicella, we examined national rates of varicella-related hospital discharges (VRHD) covering a 12-year period that included pre- and postvaccine data.

METHODS

Data from the 1988 to 1999 National Hospital Discharge Survey and population estimates from the National Center for Health Statistics were used to calculate biennial rates of VRHD. To control for coding consistency, rates of invasive disease caused by were calculated for the same time period.

RESULTS

The rate of VRHD for 1998 to 1999 (4.42 hospitalizations per 100 000 person-years) was the lowest of any of the periods measured, but this difference was not statistically significant. The same was true of VRHD limited to cases with varicella coded as the primary diagnosis. A trend toward a decrease in VRHD was observed in all age groups examined, although none was statistically significant. Calculated rates from this national data set were in agreement with prior studies using active surveillance, and the previously documented fall in hospitalizations caused by invasive disease was demonstrated using these methods.

CONCLUSIONS

Although it is uncommon for children with varicella to require hospitalization, these cases are an important contributor to cost and morbidity of varicella. In contrast to predictions of prelicensure mathematical models, there has not been a significant decrease in total or first diagnosis VRHD since the vaccine became available. Current coverage levels are below those used in prelicensure models. Increased acceptance of the varicella vaccine by parents and practitioners may aid in the further decrease of varicella-related hospitalizations.

Pediatric Liver Transplantation

Pediatric liver transplantation is a fast-growing and challenging field. Healthcare providers must stay informed of advancements in the management of liver transplant candidates and recipients. The goal of this paper is to provide nurses who care for pediatric liver transplant candidates and recipients with a review of the basic medical management of these patients, from the preoperative evaluation to postoperative care.

Vaccination with measles, mumps and rubella vaccine and varicella vaccine: safety, tolerability, immunogenicity, persistence of antibody and duration of protection against varicella in healthy children

BACKGROUND

Administration of M-M-R II (Measles, Mumps and Rubella Virus Vaccine, Live) and VARIVAX [Varicella Virus Vaccine Live (Oka/Merck)] given concomitantly at separate injection sites during the same office visit could increase vaccine compliance by reducing the number of health care visits for immunizations. We compared the safety and immunogenicity of M-M-R II and VARIVAX given concomitantly at separate sites (Group A) with administration of the two vaccines 6 weeks apart (Group B) as well as the persistence of varicella antibody and the duration of protection afforded by varicella vaccine.

METHODS

A total of 603 healthy children, ages 12 months to 6 years, with no history of measles, mumps, rubella, varicella and zoster or vaccination against these diseases, were randomized to either Group A or B and were followed for clinical reactions and serologic responses to all four viral components. Children were enrolled from August through December, 1993. Subjects were followed for 5 years to evaluate persistence of varicella antibody and breakthrough varicella rates. We compared breakthrough rates to expected attack rates in unvaccinated children to produce estimates of vaccine efficacy.

RESULTS

Both vaccine regimens were generally well-tolerated. There were no significant differences between the groups in the rates of fever, injection site reactions or rashes after vaccination. Seroconversion rates and geometric mean titers for measles, mumps and rubella were not significantly different between groups. The varicella seroconversion rate and percentage with glycoprotein-based ELISA titers > or = 5.0 units were similar between the two groups (99.5 and 92.5% vs. 100 and 94.8% for Groups A and B, respectively), but the geometric mean titers were statistically significantly different (13.2 for Group A and 17.9 for Group B). Varicella antibody persistence rates were >98 to 100% during 6 years of follow-up in both groups. Compared with historical rates, varicella vaccine efficacy during 5 years was estimated to be 90.5% (95% confidence interval, 86.2%, 95.0%) and 88.9% (95% confidence interval, 83.7%, 93.7%) in Groups A and B, respectively.

CONCLUSIONS

Administration of M-M-R II and VARIVAX concomitantly at separate injection sites or 6 weeks apart was generally well-tolerated and immunogenic in healthy children 12 months to 6 years of age. VARIVAX administered with M-M-R II induced persistent immunity and long-term protection against breakthrough varicella infection.