Partial uptake of varicella vaccine and the epidemiological effect on varicella disease in 11 day-care centers in North Carolina

Burden of varicella complications in secondary care, England, 2004 to 2017

BackgroundStrategies to control varicella vary across Europe. Evidence from established programmes has prompted the United Kingdom to re-evaluate the need for universal vaccination. The burden of complicated varicella is a key parameter in the cost-effectiveness analysis.AimOur objective was to estimate the burden of complicated varicella in England.MethodsThis electronic health record surveillance study used data from all NHS hospitals in England to identify varicella admissions between 2004 and 2017. The incidence of pre-defined complications of varicella was estimated using ICD-10 codes. Inpatient costs were calculated based on the payment rules for providers of NHS services.ResultsThere were 61,024 admissions with varicella between 2004 and 2017 and 38.1% had a recognised varicella complication. Incidence of hospitalisation increased by 25% and the proportion with complicated varicella by 24% from 2004/05 to 2016/17. The most common complications were bacterial skin infections (11.25%), pneumonia (4.82%), febrile convulsions (3.39%) and encephalitis (2.44%). Complication rates were higher in older age groups and the type of complications more severe. Length of stay for complicated varicella was 3.1 times longer than for uncomplicated varicella and inpatient costs were 72% greater.ConclusionComplicated varicella has a substantial health and economic burden. These data together with data on impact on quality of life are important in informing the cost-effectiveness analysis of universal varicella vaccination.

A double blind, randomized, active controlled study to assess the safety, tolerability and immunogenicity of measles, mumps rubella, and varicella vaccine (MMRV) manufactured using an alternative process

Vaccination against measles, mumps, rubella, and varicella is recommended for all children in the US. Limitations manufacturing Oka/Merck strain varicella-zoster virus have hampered the availability of the combination vaccine (MMRV) against these 4 viruses, which drove the need to investigate an alternative manufacturing process. Healthy children 12-to-23 months of age at 71 US sites were randomized (1:1) to receive MMRV manufactured using an alternative process (MMRVAMP) or the currently licensed MMRV. Subjects received 2 0.5 mL doses 3 months apart. Sera were collected before and 6 weeks after Dose-1. Adverse experiences (AEs) were collected for 42 d after each dose and serious AEs and events of special interest for 180 d after Dose-2. Overall, 706 subjects were randomized to MMRVAMP and 706 to MMRV and 698 and 702 received at least 1 dose of study vaccine, respectively. The risk difference in response rates and geometric mean concentrations of antibody to measles, mumps, rubella, and varicella viruses 6 weeks after Dose-1 met non-inferiority criteria for MMRVAMP versus, MMRV. Response rates met acceptability criteria for each virus, and the seroconversion rate to varicella-zoster virus was 99.5% in both groups. Vaccine-related AEs were mostly mild-to-moderate in intensity and somewhat more common after MMRVAMP. Febrile seizures occurred at similar rates in both groups during the first 42 d after each vaccine dose. MMRVAMP is non-inferior to MMRV and represents an important advancement in maintaining an adequate supply of vaccines against these diseases.

Digital epidemiology reveals global childhood disease seasonality and the effects of immunization

Public health surveillance systems are important for tracking disease dynamics. In recent years, social and real-time digital data sources have provided new means of studying disease transmission. Such affordable and accessible data have the potential to offer new insights into disease epidemiology at national and international scales. We used the extensive information repository Google Trends to examine the digital epidemiology of a common childhood disease, chicken pox, caused by varicella zoster virus (VZV), over an 11-y period. We (i) report robust seasonal information-seeking behavior for chicken pox using Google data from 36 countries, (ii) validate Google data using clinical chicken pox cases, (iii) demonstrate that Google data can be used to identify recurrent seasonal outbreaks and forecast their magnitude and seasonal timing, and (iv) reveal that VZV immunization significantly dampened seasonal cycles in information-seeking behavior. Our findings provide strong evidence that VZV transmission is seasonal and that seasonal peaks show remarkable latitudinal variation. We attribute the dampened seasonal cycles in chicken pox information-seeking behavior to VZV vaccine-induced reduction of seasonal transmission. These data and the methodological approaches provide a way to track the global burden of childhood disease and illustrate population-level effects of immunization. The global latitudinal patterns in outbreak seasonality could direct future studies of environmental and physiological drivers of disease transmission.

Varicella-zoster vaccine in the USA: success for control of disease severity, but what next?

In the period from 1990 to 1994, before the introduction of a varicella vaccine to the USA, approximately 100 deaths in otherwise healthy individuals, children and adolescents under 20 years of age, were attributable to varicella complications. The administration of a single-dose vaccine has now been widespread in the USA for nearly 10 years; however, since the effectiveness of a single dose in children under 13 years of age in an outbreak situation is approximately 80%, consideration of a second booster dose is in progress although not yet recommended. Licensure of a measles-mumps-rubella-varicella vaccine may hasten the recommendation.

Seroprevalence of antibodies against measles, rubella, mumps, varicella-zoster, and B. Pertussis in young adults of Madrid, Spain

In recent years, there has been an increase in the number of cases of certain immunopreventable diseases in our country. A high proportion of these have been recorded among the young adult population. The aim of this study was to determine the seroprevalence of antibodies against immunopreventable diseases with the greatest health impacts on the young adult population (19-39 y of age) in Madrid. We collected a total of 1,153 serum samples from healthy volunteers undergoing routine medical visits and used ELISA to determine the presence of IgG antibodies against measles, rubella, mumps, and varicella zoster, as well as Bordetella pertussis. The Pearson's χ(2) test was used to compare prevalences, the Mann-Whitney U test was used to compare means, and the Kruskal-Wallis test was applied for variables with more than 2 categories. Statistical significance was achieved with p values of<0.05. The global prevalence of antibodies was 92.1% for measles, 94.4% for rubella, 88.3% for mumps, 92.8% for varicella zoster, and 70.2% for B. pertussis. No statistically significant differences were found between genders. The prevalence of antibodies against measles was more than 95% in the group of individuals born after 1986, and the percentage of individuals susceptible to rubella was less than 5% in women born after 1986. In spite of adequate vaccination coverage, in our region, a population of young adults exists who have not achieved the objectives of the WHO for the elimination of measles and congenital rubella syndrome.

Severe complications of chickenpox in hospitalised children in the UK and Ireland

AIMS

To estimate the annual incidence of hospitalisations due to severe complications of varicella, describe the complications and estimate annual mortality.

METHODS

Active surveillance throughout the UK and Ireland for 13 months by paediatricians notifying cases to the British Paediatric Surveillance Unit and completing a questionnaire. The case definition was any child aged <16 years hospitalised with complicated varicella, as defined by a list of conditions, or admitted to ICU/HDU with varicella.

RESULTS

188 cases were notified for the surveillance period, of which 112 (0.82/100 000 children/year) met the case definition and were not duplicates. Confirmed cases had a median age of 3 years (range 0-14). The complications were: bacteraemia/septic shock (n = 30), pneumonia (n = 30), encephalitis (n = 26), ataxia (n = 25), toxic shock syndrome/toxin-mediated disease (n = 14), necrotising fasciitis (n = 7), purpura fulminans/disseminated coagulopathy (n = 5), fulminant varicella (n = 5) and neonatal varicella (n = 3). 52 children (46%) had additional bacterial infections. Six deaths were due, or possibly due, to varicella, including one intrauterine death. Four of the other five children who died (ages 2-14 years) had a pre-existing medical condition. Sequelae on discharge were reported for 41 cases (40%), most frequently ataxia or skin scarring. The median length of hospital stay was 7 days (range 1-68).

CONCLUSIONS

This study provides a minimum estimate of severe complications and death resulting from varicella in children in the UK and Ireland. Most complications, excluding deaths, occur in otherwise healthy children and thus would be preventable only through a universal childhood immunisation programme.

The comparative sero-epidemiology of varicella zoster virus in 11 countries in the European region

The European sero-epidemiology network (ESEN2) aims to standardise serological surveillance of varicella zoster virus (VZV) in 11 participant countries. In each country, serum banks were collected between 1996 and 2003 and tested for VZV antibodies. Assay results were standardised so that international comparisons could be made. Age-specific forces of infection were calculated for three age groups (<5, 5-9 and >or=10 years of age) and used to estimate the base reproduction number (R(0)) and the herd immunity threshold (H). Most VZV infection occurred in childhood, but there was a wide variation in transmissibility, with R(0) ranging from 16.9 in the Netherlands to 3.3 in Italy. Herd immunity thresholds varied from 70% in Italy to 94% in the Netherlands. There are substantial differences in VZV sero-epidemiology within the European region, which will need to be taken into account in designing national policies regarding VZV vaccination.

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.

The incidence of varicella and herpes zoster in Massachusetts as measured by the Behavioral Risk Factor Surveillance System (BRFSS) during a period of increasing varicella vaccine coverage, 1998-2003

BACKGROUND

The authors sought to monitor the impact of widespread varicella vaccination on the epidemiology of varicella and herpes zoster. While varicella incidence would be expected to decrease, mathematical models predict an initial increase in herpes zoster incidence if re-exposure to varicella protects against reactivation of the varicella zoster virus.

METHODS

In 1998-2003, as varicella vaccine uptake increased, incidence of varicella and herpes zoster in Massachusetts was monitored using the random-digit-dial Behavioral Risk Factor Surveillance System.

RESULTS

Between 1998 and 2003, varicella incidence declined from 16.5/1,000 to 3.5/1,000 (79%) overall with > or = 66% decreases for all age groups except adults (27% decrease). Age-standardized estimates of overall herpes zoster occurrence increased from 2.77/1,000 to 5.25/1,000 (90%) in the period 1999-2003, and the trend in both crude and adjusted rates was highly significant (p < 0.001). Annual age-specific rates were somewhat unstable, but all increased, and the trend was significant for the 25-44 year and 65+ year age groups.

CONCLUSION

As varicella vaccine coverage in children increased, the incidence of varicella decreased and the occurrence of herpes zoster increased. If the observed increase in herpes zoster incidence is real, widespread vaccination of children is only one of several possible explanations. Further studies are needed to understand secular trends in herpes zoster before and after use of varicella vaccine in the United States and other countries.

Effectiveness of the Oka/GSK attenuated varicella vaccine for the prevention of chickenpox in clinical practice in Israel

BACKGROUND

The varicella Oka/Merck vaccine has been shown to be very effective in clinical practice; however, several recent studies reported reduced effectiveness. The varicella Oka/GSK vaccine (Varilrix; GlaxoSmithKline Biologicals), which has been subjected to fewer effectiveness studies, was licensed in Israel for voluntary use in 2000. This study was planned to estimate the effectiveness of the varicella Oka/GSK vaccine among children 1-5 years of age.

METHODS

Recent reports of varicella were retrieved from the Tel Aviv Health District. Two age-matched control subjects who attended the same day-care center and/or resided in the same neighborhood and had not contracted varicella in the past were recruited for each varicella case. The parents of case and control subjects were interviewed regarding the history of varicella vaccination and the severity of illness.

RESULTS

A total of 151 case subjects (mean age, 2.9 +/-1.1 years) and 298 control subjects (mean age, 3.0 +/-1.1 years) were recruited. Vaccination rates for case and control subjects were 6.6% and 38.3%, respectively (P < 0.001). Disease among vaccinated children was significantly milder, as measured by several indices, including parental perception of the illness, presence of fever, time until the lesions dried and days of day care missed. Vaccine effectiveness against varicella of any severity with these figures was 88% (95% confidence interval, 77-94%), and effectiveness against moderate/severe illness was 100%.

CONCLUSIONS

Our data demonstrate that the varicella Oka/GSK vaccine used in clinical practice is highly effective in prevention of varicella (especially moderate/severe disease) among children, including those attending day-care centers.

The impact of varicella vaccination in the United States

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

Preventing varicella-zoster disease

Varicella-zoster virus (VZV), the cause of chickenpox and shingles, is a pathogen in retreat following the introduction of mass vaccination in the United States in 1995. The live attenuated Oka vaccine, which is safe and immunogenic, gives good protection against both varicella and zoster in the short to medium term. It has undoubtedly been highly effective to date in reducing all forms of varicella, especially severe disease. However, the huge pool of latent wild-type virus in the population represents a continuing threat. Both the biology and the epidemiology of VZV disease suggest that new vaccination strategies will be required over time.

Evaluating human papillomavirus vaccination programs

Human papillomavirus (HPV) has been implicated as the primary etiologic agent of cervical cancer. Potential vaccines against high-risk HPV types are in clinical trials. We evaluated vaccination programs with a vaccine against HPV-16 and HPV-18. We developed disease transmission models that estimated HPV prevalence and infection rates for the population overall, by age group, by level of sexual activity within each age group, and by sex. Data were based on clinical trials and published and unpublished sources. An HPV-16/18 vaccine for 12-year-old girls would reduce cohort cervical cancer cases by 61.8%, with a cost-effectiveness ratio of 14,583 dollars per quality-adjusted life year (QALY). Including male participants in a vaccine rollout would further reduce cervical cancer cases by 2.2% at an incremental cost-effectiveness ratio of 442,039 dollars/QALY compared to female-only vaccination. Vaccination against HPV-16 and HPV-18 can be cost-effective, although including male participants in a vaccination program is generally not cost-effective, compared to female-only vaccination.

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.

Effectiveness of live varicella vaccine

The disease burden of chickenpox to children has been described, and a lower force of neutralising antibody to varicella-zoster virus (VZV) than against measles, either after natural infection or after vaccination, has been reported. In the case of VZV, strong cell-mediated immunity may work efficiently to prevent the spread of the virus. The lower force of humoral antibody to VZV might be related to the occurrence of "breakthrough" varicella cases in a small portion of the vaccine recipients. Safety and high effectiveness of the varicella vaccine--approximately 85% effective for all diseases and 95-100% effective for moderate-to-severe diseases--have been reported. Vaccine-induced immunity persists for 10-20 years. However, concerns have been raised that universal immunisation in children may shift the susceptibility from children to adults, whose symptoms are usually moderate-to-severe. In addition, other concerns have been expressed that, due to lack of exposure to varicella in children, the elderly may develop zoster infections more frequently than before. A clear answer is difficult to give at present, although, for several reasons, such situations may be unlikely to occur.

Varicella zoster virus infections in children after the introduction of live attenuated varicella vaccine

PURPOSE OF REVIEW

Varicella zoster virus is the cause of both varicella (chickenpox) and herpes zoster (shingles). A live attenuated varicella vaccine was developed in 1974 and was approved in 1995 by the United States Food and Drug Administration for administration to both healthy children (>12 months of age) and adults who are susceptible to varicella. Many studies have shown varicella vaccine to be highly effective. Widespread use of the varicella vaccine in the United States has led to important changes in the epidemiology of the infection. The purpose of this review is to summarize the most recent and important findings regarding the impact that the widespread use of varicella vaccine has had on the epidemiology of varicella zoster infections in children.

RECENT FINDINGS

Data from the United States Centers for Disease Control and Prevention have shown a dramatic decline in the incidence of varicella (76 to 87% from 1995 to 2000), with the greatest decline observed in preschool children, as well as a reduction in the number of hospitalizations for cases of varicella. However, as the proportion of children in the United States who have received the varicella vaccine has increased there have been several recent reports in which the effectiveness of the vaccine was substantially lower than expected. In particular, reports during outbreaks of varicella in children have noted increases in breakthrough disease in children who were vaccinated before the age of 15 months, in children with asthma, in those who received the varicella vaccine soon after the measles, mumps, and rubella vaccine (<28 days), and in children who received the vaccine more than 3 years before the development of disease.

SUMMARY

Although reports of outbreaks of chickenpox in highly immunized groups have raised questions regarding the need for changes to the current vaccination policy, data undeniably indicate that immunization with varicella vaccine has been and continues to be successful in reducing the burden of disease in children and that universal immunization should continue to be a priority in the United States

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.

Variation in public and private supply of pneumococcal conjugate vaccine during a shortage

CONTEXT

In late August 2001, a serious shortage of the heptavalent pneumococcal conjugate vaccine (PCV7) developed in 34 state immunization programs. In September 2001, the Centers for Disease Control and Prevention published revised recommendations advising physicians to prioritize PCV7 to specific groups of children. The effect of the shortage at the practice level is unknown.

OBJECTIVE

To determine the variation between public and private markets in the supply of PCV7 and the nature and extent of the PCV7 shortage at the practice level.

DESIGN, SETTING, AND PARTICIPANTS

Semistructured interviews with office staff responsible for ordering vaccines at private practices in 12 states were conducted between October 19 and November 2, 2001.

MAIN OUTCOME MEASURES

Variation in supply of PCV7 obtained from public sources and through purchase on the private market. Supply was characterized into 3 categories: "no problem," "problem obtaining a consistent supply," and "out of stock."

RESULTS

Interviews were completed at 405 practices, representing a response rate of 74%. Overall, 51% of practices reported at least 1 episode of being out of stock of public PCV7 and 64% of private PCV7, with significant state-to-state variation. Only 2 of 12 study states had a substantially higher proportion of practices experiencing out-of-stock episodes for public compared with private PCV7, while in 6 states public PCV7 was less frequently out of stock than private PCV7. Only 23% of practices in this study altered their administration policy for private PCV7, while 27% altered their policy for public PCV7.

CONCLUSIONS

The distribution and supply of PCV7 varied between public and private supplies and between states during the shortage. Few practices changed their administration schedules in response to revised recommendations.

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.

Exposure to varicella boosts immunity to herpes-zoster: implications for mass vaccination against chickenpox

We present data to confirm that exposure to varicella boosts immunity to herpes-zoster. We show that exposure to varicella is greater in adults living with children and that this exposure is highly protective against zoster (Incidence ratio=0.75, 95% CI, 0.63-0.89). The data is used to parameterise a mathematical model of varicella zoster virus (VZV) transmission that captures differences in exposure to varicella in adults living with and without children. Under the 'best-fit' model, exposure to varicella is estimated to boost cell-mediated immunity for an average of 20 years (95% CI, 7-41years). Mass varicella vaccination is expected to cause a major epidemic of herpes-zoster, affecting more than 50% of those aged 10-44 years at the introduction of vaccination.

The effect of vaccination on the epidemiology of varicella zoster virus

Varicella zoster virus (VZV) causes chickenpox (varicella) on primary exposure and can reactivate later in life to cause shingles (zoster). As primary infection is more serious in adults than children, and exposure to the virus might boost the immune response to both chickenpox and shingles, there are two main concerns regarding infant VZV vaccination: that it could lead to an increase in adult disease; and/or that it could lead to a temporary increase in the incidence of shingles. This paper reviews the evidence for such outcomes. The consensus view of mathematical modelling studies is that the overall varicella associated burden is likely to decrease in the long term, regardless of the level of vaccine coverage. On the other hand, recent evidence suggests that an increase in zoster incidence appears likely, and the more effective vaccination is at preventing varicella, the larger the increase in zoster incidence. Targeted vaccination of susceptible adolescents and/or the contacts of high-risk individuals can be effective at preventing disease in these individuals with minimal risk to the community. However, targeted strategies would not prevent most disease (including most severe disease), and will not lead to a long-term reduction in the incidence of zoster. Understanding the mechanisms for maintaining immunity against varicella and zoster is critical for predicting the long-term effects of vaccination. Meanwhile sensitive surveillance of both chickenpox and shingles is essential in countries that have implemented, or are about to implement, varicella vaccination.

Varicella: a vaccine preventable disease?

OBJECTIVES

To present a review of varicella disease, vaccine development and implementation of universal vaccination, discuss common questions about the vaccine and the epidemiology of the disease since licensure of the varicella vaccine.

METHODS

Review the incidence of complications from varicella disease prior to vaccine licensure, safety of the varicella vaccine from clinical trials and post-marketing surveillance data, the impact of the vaccine on disease incidence where high vaccine coverage has been achieved, and address some barriers to vaccination. Raise issues that developed since 1995.

RESULTS

The safety data gathered during the 20-year-gestation period of this vaccine prior to licensure has been confirmed. The vaccine works-in areas where vaccine coverage is over 70%, there has been a decline in disease, most marked in the age group with the best vaccine coverage (the 1-4-year olds), leading to a concern that unexposed susceptible children may reach adulthood and remain susceptible unless better practice of universal vaccination of ALL susceptible is practiced.

CONCLUSIONS

Varicella disease has declined in areas with moderate vaccine coverage. Continued implementation of existing vaccine policies will lead to further reductions of varicella morbidity and mortality throughout the USA.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.

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

OBJECTIVE

To document the duration of protection afforded by Oka/Merck varicella vaccine over a 7-year period.

STUDY DESIGN

The subjects were healthy children 1 to 12 years of age originally enrolled in clinical studies to evaluate the primary immune response to varicella vaccine 6 weeks after vaccination. Each was monitored for antibody persistence, breakthrough infection, and household exposure to varicella to produce estimates of vaccine efficacy.

RESULTS

The 6-year cumulative varicella antibody persistence rate was 99.5% (95% CI: 98.9%, 100.0%). The annual breakthrough rate through 7 years ranged from 0.2% to 2.3% per year; the estimated cumulative event rate was 6.5%. Comparison of the observed average annual breakthrough rate with the age-adjusted expected annual incidence rate of varicella in unvaccinated children corresponded to an estimated vaccine efficacy of 93.8% to 94.6%. Eighty vaccinated children were exposed to varicella in the household, resulting in 8 (10%) cases of infection. When compared with the historical attack rate of 86.8% in unvaccinated susceptible persons exposed to varicella in the household, this yields an estimated vaccine efficacy of 88.5% (95% CI: 80.9%, 96.1%). Varicella cases in vaccinated children generally were mild.

CONCLUSION

The live attenuated varicella vaccine is highly effective in inducing persistent immunity and long-term protection against breakthrough varicella infection.