Varicella disease after introduction of varicella vaccine in the United States, 1995-2000

Comparing Active and Passive Varicella Surveillance in Philadelphia, 2005–2010: Recommendations for the Transition to Nationwide Passive Varicella Disease Surveillance

Objective.

The Philadelphia Department of Public Health (PDPH) conducts active surveillance for varicella in West Philadelphia. For its approximately 300 active surveillance sites, PDPH mandates biweekly reports of varicella (including zero cases) and performs intensive case investigations. Elsewhere in Philadelphia, surveillance sites passively report varicella cases, and abbreviated investigations are conducted. We used active varicella surveillance program data to inform the transition to nationwide passive varicella surveillance.

Methods.

We compared classification of reported cases, varicella disease incidence, and reporting completeness for active and passive surveillance areas for 2005–2010. We assessed reporting completeness using capture-recapture analysis of 2- to 18-year-old cases reported by schools/daycare centers and health-care providers.

Results.

From 2005 to 2010, PDPH received 3,280 passive and 969 active surveillance varicella case reports. Most passive surveillance reports were classified as probable cases (18% confirmed, 56% probable, and 26% excluded), whereas nearly all of the active surveillance reports were either confirmed or excluded (36% confirmed, 11% probable, and 53% excluded). Overall incidence rates calculated using confirmed/probable cases were similar in the active and passive surveillance areas. Detection of laboratory-confirmed, breakthrough, and moderate-to-severe cases was equivalent for both surveillance areas.

Conclusions.

Although active surveillance for varicella results in better classified cases, passive surveillance provides comparable data for monitoring disease trends in breakthrough and moderate-to-severe varicella. To further improve passive surveillance in the two-dose-varicella vaccine era, jurisdictions should consider conducting periodic enhanced surveillance, encouraging laboratory testing, and collecting additional varicella-specific variables for passive surveillance.

Different vaccination strategies in Spain and its impact on severe varicella and zoster

Varicella vaccines available in Spain were marketed in 1998 and 2003 for non-routine use. Since 2006 some regions decided to include varicella vaccination in their regional routine vaccination programmes at 15-18 months of age. Other regions chose the strategy of vaccinating susceptible adolescents. This study shows the trends in severe varicella zoster virus infections through the analysis of the hospital discharges related to varicella and herpes zoster in the general population from 2005 to 2010 in Spain. A total of 11,125 hospital discharges related to varicella and 27,736 related to herpes zoster were reported during the study period. The overall annual rate of hospitalization was 4.14 cases per 100,000 for varicella and 10.33 cases per 100,000 for herpes zoster. In children younger than 5 years old varicella hospitalization rate significantly decreased from 46.77 in 2005 to 26.55 per 100,000 in 2010. The hospitalization rate related to herpes zoster slightly increased from 9.71 in 2005 to 10.90 per 100,000 in 2010. This increase was mainly due to the significant increase occurring in the >84 age group, from 69.55 to 97.68 per 100,000. When gathering for regions taking into account varicella vaccine strategy, varicella related hospitalizations decreased significantly more in those regions which included the vaccine at 15-18 months of age as a routine vaccine comparing with those vaccinating at 10-14 years old. No significant differences were found in herpes zoster hospitalization rates regarding the varicella vaccination strategy among regions. Severe varicella infections decreased after implementation of varicella vaccination in Spain. This decrease was significantly higher in regions including the vaccine at 15-18 months of age compared with those vaccinating susceptible adolescents.

Impact of a routine two-dose varicella vaccination program on varicella epidemiology

OBJECTIVE

One-dose varicella vaccination for children was introduced in the United States in 1995. In 2006, a second dose was recommended to further decrease varicella disease and outbreaks. We describe the impact of the 2-dose vaccination program on varicella incidence, severity, and outbreaks in 2 varicella active surveillance areas.

METHODS

We examined varicella incidence rates and disease characteristics in Antelope Valley (AV), CA, and West Philadelphia, PA, and varicella outbreak characteristics in AV during 1995-2010.

RESULTS

In 2010, varicella incidence was 0.3 cases per 1000 population in AV and 0.1 cases per 1000 population in West Philadelphia: 76% and 67% declines, respectively, since 2006 and 98% declines in both sites since 1995; incidence declined in all age groups during 2006-2010. From 2006-2010, 61.7% of case patients in both surveillance areas had been vaccinated with 1 dose of varicella vaccine and 7.5% with 2 doses. Most vaccinated case patients had <50 lesions with no statistically significant differences among 1- and 2-dose cases (62.8% and 70.3%, respectively). Varicella-related hospitalizations during 2006-2010 declined >40% compared with 2002-2005 and >85% compared with 1995-1998. Twelve varicella outbreaks occurred in AV during 2007-2010, compared with 47 during 2003-2006 and 236 during 1995-1998 (P < .01).

CONCLUSIONS

Varicella incidence, hospitalizations, and outbreaks in 2 active surveillance areas declined substantially during the first 5 years of the 2-dose varicella vaccination program. Declines in incidence across all ages, including infants who are not eligible for varicella vaccination, and adults, in whom vaccination levels are low, provide evidence of the benefit of high levels of immunity in the population.

Impact of universal two-dose vaccination on varicella epidemiology in Navarre, Spain, 2006 to 2012

In 2007 in Navarre, Spain, universal varicella vaccination with two doses of Varivax was introduced in the childhood immunisation schedule for children aged 15 months and three years. This study describes changes in the epidemiology of varicella in the period 2006 to 2012 and evaluates vaccination effectiveness using epidemiological surveillance data. The incidence of varicella in children aged 0 to 14 years decreased by 98.1%, from 50.1 cases per 1,000 inhabitants in 2006, to 1.0 per 1,000 in 2012. Children aged one to eight years were the vaccinated cohorts, and their incidence of varicella decreased by 98.5% (p<0.0001). In unvaccinated age groups, important reductions were also achieved between 2006 and 2012: 90.5% (p<0.0001) in infants under one year of age, and 89.4% (p<0.0001) in children aged nine years. In the period 2006 to 2012, the hospital admissions rate for varicella or its complications decreased by 89.0%, and in 2012, there was only one admission of a newborn with neonatal varicella. Vaccine effectiveness for at least one dose was 96.8% (95% confidence interval: 96.3-97.2%). Universal vaccination with two doses has reduced varicella circulation to minimum levels within five years and has proved highly effective.

Varicella disease in Beijing in the era of voluntary vaccination, 2007 to 2010

BACKGROUND

In China, varicella vaccine has been available in the private sector to children ≥12 months of age since 1998 with a single-dose indication. In December 2006, varicella became a notifiable disease in Beijing. We used surveillance data to describe varicella vaccine uptake from 2005 to 2010 and varicella epidemiology in Beijing from 2007 to 2010.

METHODS

Limited sociodemographic and clinical information was available from the passive surveillance system. Varicella vaccine coverage was estimated for each year for children born between 2004 and 2008 using the number of children in the immunization registry of each birth year as the denominator without adjustment for history of varicella.

RESULTS

Vaccine coverage increased within each birth cohort between 2005 and 2010. The coverage at 2 years of age increased from 62.4% in 2005 to 74.1% in 2010 and was 80.4% in children 3-6 years of age in 2010. Between 2007 and 2010, 15,544 to 18,256 varicella cases were reported annually with stable overall incidence (range: 1.0-1.1/1000 persons), but the incidence in children 1-4 years of age decreased significantly from 6.2 per 1000 children in 2007 to 4.4 per 1000 children in 2010 (P < 0.001). Among adults (≥20 years of age), there were significant increases in the number and proportion of cases from 2557 (16.5%) in 2007 to 4277 (23.4%) in 2010 (P < 0.001).

CONCLUSIONS

Moderately high 1-dose vaccine coverage in young children has been achieved with declining disease incidence, but varicella remains a common, seasonal disease in the population. Current epidemiology suggests that a government-funded varicella vaccine program that includes catch-up vaccination for older children, adolescents and adults needs consideration.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Perspectives on the impact of varicella immunization on herpes zoster. A model-based evaluation from three European countries

The introduction of mass vaccination against Varicella-Zoster-Virus (VZV) is being delayed in many European countries because of, among other factors, the possibility of a large increase in Herpes Zoster (HZ) incidence in the first decades after the initiation of vaccination, due to the expected decline of the boosting of Cell Mediated Immunity caused by the reduced varicella circulation. A multi-country model of VZV transmission and reactivation, is used to evaluate the possible impact of varicella vaccination on HZ epidemiology in Italy, Finland and the UK. Despite the large uncertainty surrounding HZ and vaccine-related parameters, surprisingly robust medium-term predictions are provided, indicating that an increase in HZ incidence is likely to occur in countries where the incidence rate is lower in absence of immunization, possibly due to a higher force of boosting (e.g. Finland), whereas increases in HZ incidence might be minor where the force of boosting is milder (e.g. the UK). Moreover, a convergence of HZ post vaccination incidence levels in the examined countries is predicted despite different initial degrees of success of immunization policies. Unlike previous model-based evaluations, our investigation shows that after varicella immunization an increase of HZ incidence is not a certain fact, rather depends on the presence or absence of factors promoting a strong boosting intensity and which might or not be heavily affected by changes in varicella circulation due to mass immunization. These findings might explain the opposed empirical evidences observed about the increases of HZ in sites where mass varicella vaccination is ongoing.

Review of the United States universal varicella vaccination program: Herpes zoster incidence rates, cost-effectiveness, and vaccine efficacy based primarily on the Antelope Valley Varicella Active Surveillance Project data

In a cooperative agreement starting January 1995, prior to the FDA's licensure of the varicella vaccine on March 17, the Centers for Disease Control and Prevention (CDC) funded the Los Angeles Department of Health Services' Antelope Valley Varicella Active Surveillance Project (AV-VASP). Since only varicella case reports were gathered, baseline incidence data for herpes zoster (HZ) or shingles was lacking. Varicella case reports decreased 72%, from 2834 in 1995 to 836 in 2000 at which time approximately 50% of children under 10 years of age had been vaccinated. Starting in 2000, HZ surveillance was added to the project. By 2002, notable increases in HZ incidence rates were reported among both children and adults with a prior history of natural varicella. However, CDC authorities still claimed that no increase in HZ had occurred in any US surveillance site. The basic assumptions inherent to the varicella cost-benefit analysis ignored the significance of exogenous boosting caused by those shedding wild-type VZV. Also ignored was the morbidity associated with even rare serious events following varicella vaccination as well as the morbidity from increasing cases of HZ among adults. Vaccine efficacy declined below 80% in 2001. By 2006, because 20% of vaccinees were experiencing breakthrough varicella and vaccine-induced protection was waning, the CDC recommended a booster dose for children and, in 2007, a shingles vaccination was approved for adults aged 60 years and older. In the prelicensure era, 95% of adults experienced natural chickenpox (usually as children)-these cases were usually benign and resulted in long-term immunity. Varicella vaccination is less effective than the natural immunity that existed in prevaccine communities. Universal varicella vaccination has not proven to be cost-effective as increased HZ morbidity has disproportionately offset cost savings associated with reductions in varicella disease. Universal varicella vaccination has failed to provide long-term protection from VZV disease.

Secular trends of chickenpox among military population in Israel in relation to introduction of varicella zoster vaccine 1979-2010

Chickenpox is a contagious disease caused by the varicella zoster virus. There is scarce data on long-term trends of chickenpox and its relation to vaccinations practices. We aimed to evaluate trends of chickenpox in a military population during the period 1979-2010 and to assess temporal associations in relation with the introduction of varicella zoster vaccine to the civilian population in Israel in 2000. The archives of the Epidemiology Section of the Israel Defense Forces, where chickenpox is a notifiable disease, were reviewed for all cases of chickenpox from January 1, 1979-December 31, 2010. Annual and monthly incidence rates were calculated and analyzed in relation to vaccine introduction. Between 1979-2000, incidence rates fluctuated around 10 cases per 10,000 soldiers without a clear trend. Since 2000 there has been a dramatic 10-fold decline in incidence, especially notable since 2008, from eight per 10,000 soldiers in 2000 to the lowest rate ever recorded, in 2009, of 0.57 cases per 10,000 soldiers. A seasonal sinusoidal pattern was clearly demonstrated, with rising incidence from November to May followed by a gradual decline to October. The results of this long-term study suggest that the rates of chickenpox in the military population have significantly declined since the introduction of the vaccine to the civilian population in Israel and almost disappeared completely since 2008 as the vaccine was included in the state-funded routine childhood immunization schedule. These findings underscore the need for a strong surveillance system and will aid in determing vaccination policies.

Effectiveness of one and two doses of varicella vaccine in preventing laboratory-confirmed cases in children in Navarre, Spain

Varicella vaccine effectiveness was evaluated in a case-control study in Navarre, Spain, in 2010-2012. The cases were 54 children aged 15 months to 10 years with a diagnosis of varicella confirmed by polymerase-chain-reaction. Each case was matched with eight controls by pediatric practice, district of residence and date of birth. The effectiveness was 87% (95% confidence interval: 60% to 97%) for one dose of vaccine and 97% (80% to 100%) for two doses. A single dose was 93% (34% to 100%) effective in the first year, which declined to 61% (95% CI: -64% to 94%) after the third year. In conclusion, varicella vaccine is highly effective in preventing confirmed cases, although this effect declines over time since the first dose. A second dose helps to reestablish very high levels of effectiveness and to reduce the risk of breakthrough varicella.

[Early presentation of breakthrough varicella in vaccinated children]

INTRODUCTION

The introduction of a routine varicella vaccination program for children has achieved a significant reduction in morbidity and mortality due to varicella. However, there is still an incidence of chickenpox in those vaccinated, called "varicella breakthrough" (VB). This has led to the inclusion of a 2nd dose vaccination schedule, at an age which could be too late.

PATIENTS AND METHODS

This study presents 23 cases of children diagnosed with VB (mean age at diagnosis 4.85 years) who had been vaccinated with one dose of varicella vaccine (mean age of vaccination 2.37 years).

RESULTS

The mean time between the vaccine and the disease was 2.48 years, with a median of 2.0 years. VB was diagnosed in 13% of children who had been vaccinated the previous year, and 52% diagnosed in the previous two. Therefore many of these patients had suffered the disease before the recommended time of administration of the second dose of vaccine according to the current vaccine schedules.

CONCLUSIONS

To avoid these vaccine failures, it would be appropriate to bring the two doses of varicella vaccine closer, or even assess the pattern of two consecutive doses.

Varicella vaccines

BACKGROUND

Varicella zoster virus infection (VZV) is widespread and clinically important as the cause of varicella pneumonitis and meningoencephalitis (a complication of primary infection/zoster) and post-herpetic neuralgia (a complication of zoster/secondary infection). The use of live-attenuated varicella vaccine to reduce the burden of these diseases has been established in many countries for a number of years.

SOURCES OF DATA

Original papers and review articles including guidelines and recommendations by the American Academy of Paediatrics Committee on Infectious Diseases, the Advisory Committee on Immunization Practices and EuroSurveillance.

AREAS OF AGREEMENT

Immunoassay of VZV IgG by enzyme immunosorbent assay is used as a surrogate marker for previous primary infection or successful immunization. Patients who have had natural primary infection do not require vaccination against varicella. Live VZV vaccines are safe and effective at protecting against disease caused by VZV. To ensure long-term protection, a two-dose immunization regime is strongly recommended, due to significant waning of protection following a single dose. Universal two-dose immunization has been shown to be cost-effective in Western temperate countries. In many countries, routine vaccination of children is recommended but, due to cost, often not provided by universal programmes. Cost-effectiveness of a universal programme will be determined by the baseline rate of severe varicella disease.

AREAS OF CONTROVERSY

No international consensus exists: measurement of VZV immunity or cost-effectiveness of introducing VZV vaccination to a country. Decisive factors will include the pre-vaccination burden of VZV-associated disease.

The effect of funded varicella immunization programs on varicella-related hospitalizations in IMPACT centers, Canada, 2000-2008

BACKGROUND

The 12 Immunization Monitoring Program, Active (IMPACT) centers that represent 90% of pediatric tertiary care beds in Canada conducted active surveillance for varicella-related hospitalizations and complications from 1999 onward, after varicella vaccine was authorized. Publicly funded routine immunization programs at 12 or 15 months of age were introduced by 5 provinces and territories (prov/terr) in 2000 to 2002 (earlier programs, EP) and by 8 prov/terr in 2004 to 2007 (later programs, LP).

OBJECTIVE

To determine whether the number of varicella-related hospitalized cases had declined by 2008 at 12 IMPACT centers after the sequential introduction of publicly funded varicella immunization programs in Canada.

METHODS

Varicella-related hospitalizations from 2000 to 2008 in the prov/terr with EP were under surveillance by 3 IMPACT centers (Halifax, Edmonton, Calgary), whereas the prov/terr with LP were under surveillance by the remaining 9 centers. The age, gender, underlying health status, varicella complications, and length of stay in hospital and the pediatric intensive care unit were documented. Breakthrough cases were identified and their clinical characteristics described.

RESULTS

Between 2000 and 2008, the number of varicella-related hospitalized cases in IMPACT centers declined relatively sooner in prov/terr with EP (by 2002 to 2003), as compared to those with LP (only by 2007 to 2008). In 2008, varicella-related hospitalized cases declined by 88% in the EP centers, and by 81% in the LP centers. In all IMPACT centers, the greatest decline occurred in the 1-4 years age group (90% decline), with smaller declines in both <1 year and 5-9 years age groups (78% and 76% decline, respectively). Breakthrough disease accounted for 39 (2%) cases, with the proportion due to breakthrough increasing from 0.9% in 2000 to 2001, to 2% in 2003 to 2004 and 9.5% in 2007 to 2008. The majority (72%) of breakthrough cases were in immunocompromised children.

CONCLUSIONS

Publicly funded varicella vaccination programs have led to a significant decline in varicella-related hospitalizations in Canadian children, as a result of direct effects of the program beginning within 1 to 2 years after the start, as well as probable indirect protection of children outside the vaccinated cohort.

The controversy of varicella vaccination in children with acute lymphoblastic leukemia

BACKGROUND

The available guidelines for varicella vaccination of susceptible children with acute lymphoblastic leukemia (ALL) have become increasingly conservative. However, vaccination of those who have remained in continuous complete remission for 1 year and are receiving chemotherapy is still considered a reasonable option. There is little available data to allow a comparison of the risk versus benefit of vaccinating these patients.

PROCEDURE

We retrospectively reviewed mortality due to varicella in the records of 15 pediatric ALL study groups throughout Europe, Asia, and North America during the period 1984-2008.

RESULTS

We found that 20 of 35,128 children with ALL (0.057%; 95% confidence interval [CI], 0.037-0.088%) died of VZV infection. The mortality rate was lower in North America (3 of 11,558 children, 0.026%; 95% CI, 0.009-0.076%) than in the Asian countries (2 of 4,882 children, 0.041%; 95% CI, 0.011-0.149%) and in Europe (15 of 18,688 children, 0.080%; 95% CI, 0.049-0.132%) consistent with the generally higher rate of VZV vaccination in North America. Fourteen of the 20 patients (70%) died during the first year of treatment for ALL. One death was attributed to varicella vaccination.

CONCLUSIONS

The negligible rate of fatal varicella infection in children with ALL, the risk that accompanies vaccination, and the necessity of withholding chemotherapy for vaccination appear to outweigh the potential benefit of varicella vaccination for children during treatment of ALL.

Varicella in infants after implementation of the US varicella vaccination program

OBJECTIVE

To describe varicella disease in infants since implementation of the varicella vaccination program in the United States.

PATIENTS AND METHODS

From 1995 to 2008, demographic, clinical, and epidemiologic data on cases of varicella in infants were collected prospectively through a community-based active surveillance project. We examined disease patterns for infants in 2 age groups: 0 to 5 and 6 to 11 months.

RESULTS

Infant varicella disease incidence declined 89.7% from 1995 to 2008. Infants aged 0 to 5 months had milder clinical disease than those aged 6 to 11 months: ≥50 lesions, 49% vs 58% (P = .038); fever (body temperature > 38°C), 12% vs 21% (P = .014); and varicella-related complications, 6% vs 14% (P = .009), respectively. Age was an independent predictor of the occurrence of complications.

CONCLUSIONS

The varicella vaccination program has resulted in substantial indirect benefits for infants, who are not eligible for vaccination. Presence of maternal varicella-zoster virus antibodies might explain attenuated disease in very young infants likely born to mothers with history of varicella. Although varicella disease incidence has declined, exposure to varicella-zoster virus continues to occur. Improving varicella vaccination coverage in all age groups will further reduce the risk of varicella exposure and protect those not eligible for varicella vaccination.

Vaccination coverage among adolescents and risk factors associated with incomplete immunization

The compliance with vaccination recommendations in adolescence has not been well documented in Greece. The aims of the present study were to estimate the vaccination coverage in a sample of adolescents and to identify risk factors associated with incomplete immunization. Α total of 1,005 adolescents aged 11 to 19 years who were outpatient visitors at an Adolescent Health Unit were included in this study. Participation required parental presence and consent and presentation of the official Child Health Booklet, from which immunizations were transcribed. The highest coverage rates were observed for childhood immunizations: poliomyelitis and hepatitis B (both 96%), measles/mumps/rubella (MMR; 93.1%), and meningitidis C (MenC; 83.4%). By contrast, lower rates were shown for the booster dose of tetanus/diphtheria/pertussis (39.6%), for hepatitis A (HAV; 59.1%), for the varicella vaccine (13.8% among adolescents without disease history), and among girls for the human papillomavirus vaccine (11.9%). We found a significant association between age and series completion for MMR, MenC, and HAV, with lower uptake among older adolescents . Overall, 22.7% of study participants were fully vaccinated according to criteria employed. In particular, non-urban residents, non-nationals, and females had lower likelihood of being fully vaccinated. In conclusion, our findings suggest suboptimal vaccination coverage among our sample's adolescents, mandating that every effort should be made to increase uptake, particularly among the geographically dispersed and the culturally diverse and female adolescents.

Impact of universal vaccination on the epidemiology of varicella in Veneto, Italy

In 2005, universal varicella vaccination was introduced in the Veneto region, Italy. We examined trends in varicella incidence and hospitalization rates before and after vaccine introduction, and applied statistical models to assess vaccine effectiveness. Varicella incidence rates for 2000-2008 were calculated from the mandatory regional surveillance data and from a special surveillance system based on reports from a sample of family pediatricians that during the study period followed more than 40,000 children. To evaluate hospital admission rates, we analyzed the regional hospital discharge registry. The vaccine coverage rate was 6.8% in the 2004 birth-cohort and 78.6% in the 2008 cohort. Varicella incidence in 0-14 year-olds was 6136.8/100,000 person-years in 2000 and 4004.8 in 2008; hospitalization rates were 18.7 and 8.4. Incidence rates significantly decreased 2.5 years after beginning the universal vaccination, while hospitalization rates showed a significant decrease one year earlier. There was a remarkable decline of both varicella incidence and hospitalizations especially in 1-4 year-old children. This study confirms the positive impact of universal vaccination.

Safety of a second dose of varicella vaccine administered at 4 to 6 years of age in healthy children in Argentina

Varicela Biken [Live varicella Biken vaccine (strain Oka)] is an effective and safe vaccine for the prevention of varicella infection. Although the recommended schedule in all age groups (children, adolescents and adults) is a single dose, physicians in some countries follow the 2007 recommendation of the US Advisory Committee on Immunization Practices (ACIP) which recommends "implementation of a routine 2-dose varicella vaccination program for children, with the first dose administered at age 12--15 months and the second dose at age 4--6 years." ( 1) Therefore, cases can arise when two doses of Varicela Biken are given even though the ACIP guidelines are a response to the US epidemiological situation and for US licensed products based on the Oka/Merck and the Oka-RIT strains (Varicela Biken is not registered in US). The aim of this study is to ascertain the safety of a second dose of Varicela Biken in children who have been previously vaccinated with the same vaccine. In this study, children, 4-6 years of age who had been previously vaccinated with Varicela Biken, received a single 0.5 mL dose of live attenuated varicella virus vaccine containing at least 1000 Plaque Forming Units (PFU) attenuated live Varicella-zoster virus (Oka strain). Participants were monitored for 30 minutes after vaccination. Predefined injection site and systemic reactions were solicited during the subsequent seven days. Unsolicited injection site reactions and unsolicited systemic events were collected throughout the study. Any serious adverse events occurring throughout the study were reported to the sponsor's pharmacovigilance department. One hundred and twenty two children were recruited and all provided safety data. There were no immediate adverse events or injection site reactions. Forty three percent of participants reported injection site reactions and 22.1% reported systemic reactions on solicitation during the seven days after vaccination. During the 30 day monitoring period, 43 participants reported a total of 66 adverse events. Seven participants reported a total of eight unsolicited events that were assessed as related to the vaccine or where the relationship to vaccination was unknown. Five of these eight events were injection site reactions and all were mild, systemic reactions included mild rash (1 case) and fever (2 cases). There was a single serious adverse event that was not related to the study medication (subject was a passenger in a motor vehicle accident). A second dose of Varicela Biken was well tolerated and showed no significant safety issues in this population of previously vaccinated children.

Population-based incidence of herpes zoster after introduction of a publicly funded varicella vaccination program

BACKGROUND

Past varicella infection (chicken pox) may reactivate into herpes zoster (shingles). Varicella vaccination leads to a reduction in cases of varicella that may in turn increase herpes zoster rates due to reduction in the immune boosting effect of exposure to varicella zoster virus against varicella reactivation. We assessed the impact of childhood varicella vaccination in Ontario, Canada on zoster incidence and healthcare visits, and established baseline zoster rates prior to zoster vaccine introduction.

METHODS

We used population-based, administrative databases to identify zoster incidence and healthcare use from April 1992 to March 2010.

RESULTS

After routine varicella vaccination, zoster incidence rates decreased 29% for children aged 0-9 and changed minimally for other ages. Age-standardized rates of hospitalizations during the study period declined by 53%, while outpatient rates declined by 9%. The annual zoster incidence for those 60 or older was 740 per 100,000.

CONCLUSIONS

In the early post-varicella vaccination period, incidence rates of medically attended herpes zoster did not increase for the overall population and decreased moderately for children 9 years and younger, the age group targeted for varicella vaccination.

The incidence of varicella and herpes zoster in Taiwan during a period of increasing varicella vaccine coverage, 2000-2008

The introduction and the widespread use of the varicella vaccine in Taiwan has led to a 75-80% decrease in the incidence of varicella in children. However the vaccine's long-term impact on the incidence of herpes zoster (HZ) has attracted attention. By controlling gender, underlying diseases, and age effects, a Poisson regression was applied on the 2000-2008 chart records of 240 000 randomly selected residents who enrolled in the Universal National Health Insurance. The results show that, as the vaccine coverage in children increases, the incidence of varicella decreases. However, the incidence of HZ increased even before the implementation of the free varicella vaccination programme in 2004, particularly in females. The increase in the incidence of HZ cannot be entirely and directly attributed to the widespread vaccination of children. Continuous monitoring is needed to understand the secular trends in HZ before and after varicella vaccination in Taiwan and in other countries.

Effectiveness of state-level vaccination mandates: evidence from the varicella vaccine

This paper utilizes longitudinal data on varicella (chickenpox) immunizations in order to estimate the causal effects of state-level school-entry and daycare-entry immunization mandates within the United States. We find significant causal effects of mandates upon vaccination rates among preschool children aged 19-35 months; these effects appear in the year of mandate adoption, peak two years after adoption, and show a minimal difference from the aggregate trend about six years after adoption. For a mandate enacted in 2000, the model and estimates imply that roughly 20% of the short-run increase in state-level immunization rates was caused by the mandate introduction. We find no evidence of differential effects for different socioeconomic groups. Combined with previous cost-benefit analyses of the varicella vaccine, the estimates suggest that state-level mandates have been effective from an economic standpoint.

Policy statement—Prevention of varicella: update of recommendations for use of quadrivalent and monovalent varicella vaccines in children

Two varicella-containing vaccines are licensed for use in the United States: monovalent varicella vaccine (Varivax [Merck & Co, Inc, West Point, PA]) and quadrivalent measles-mumps-rubella-varicella vaccine (MMRV) (ProQuad [Merck & Co, Inc]). It is estimated from postlicensure data that after vaccination at 12 through 23 months of age, 7 to 9 febrile seizures occur per 10,000 children who receive the MMRV, and 3 to 4 febrile seizures occur per 10,000 children who receive the measles-mumps-rubella (MMR) and varicella vaccines administered concurrently but at separate sites. Thus, 1 additional febrile seizure is expected to occur per approximately 2300 to 2600 children 12 to 23 months old vaccinated with the MMRV, when compared with separate MMR and varicella vaccine administration. The period of risk for febrile seizures is from 5 through 12 days after receipt of the vaccine(s). No increased risk of febrile seizures is seen among patients 4 to 6 years of age receiving MMRV. Febrile seizures do not predispose to epilepsy or neurodevelopmental delays later in life and are not associated with long-term health impairment. The American Academy of Pediatrics recommends that either MMR and varicella vaccines separately or the MMRV be used for the first dose of measles, mumps, rubella, and varicella vaccines administered at 12 through 47 months of age. For the first dose of measles, mumps, rubella, and varicella vaccines administered at ages 48 months and older, and for dose 2 at any age (15 months to 12 years), use of MMRV generally is preferred over separate injections of MMR and varicella vaccines.

Herpes zoster in Germany: quantifying the burden of disease

BACKGROUND

Herpes zoster (HZ) is caused by a reactivation of the varicella-zoster-virus (VZV) and mainly affects individuals aged≥50 years. Vaccines have been licensed or are under development that can protect against HZ and its main complication postherpetic neuralgia (PHN). In Germany, the burden of disease caused by HZ is not well known. To support the decision making process related to a potential vaccination recommendation, we estimated annual HZ disease burden in people aged≥50 years in Germany by utilizing various data sources.

METHODS

We assessed for 2007 and 2008 HZ-outpatient incidence (number of cases per 1,000 person-years, PY) by utilizing the Association of Statutory Health Insurance Physicians (ASHIP) database, which contains nationwide routine outpatient data. For the same time period annual number of HZ-inpatients and HZ-associated deaths were identified by using the Federal Health Monitoring System (FHM). PHN-incidence and loss of quality-adjusted life years (QALYs) caused by HZ were calculated by multiplying number of identified HZ-patients with upper and lower limit estimates for proportion of HZ-cases developing PHN and HZ-related QALY, respectively.

RESULTS

For the study period we identified an annual average of 306,511 HZ-outpatients aged 50+, resulting in a HZ-incidence of 9.6/1,000 PY. A total 14,249 HZ-associated inpatients and 66 deaths were reported in both years on average. HZ-incidence increased by age from 6.21 in people 50-54 years to 13.19 per 1,000 PY in people aged≥90 years. Females were significantly more frequently affected than males in terms of outpatient HZ-incidence (11.12 vs. 7.8 per 1,000 PY), inpatient HZ-incidence (0.51 vs. 0.38 per 1,000 PY) and mortality (0.29 vs. 0.10 per 100,000 PY). PHN-incidence was estimated to range between 0.43 and 1.33 per 1,000 PY. Based on these figures, there were between 3,065 to 24,094 QALYs lost due to HZ in persons aged≥50 years in Germany per annum.

CONCLUSION

Our study provides important baseline estimates for HZ-related disease burden in Germany. HZ poses a considerable burden on the health care system in Germany both in terms of outpatient and inpatient services. Follow-up assessments of HZ disease burden are needed to monitor the impact of VZV-vaccinations in Germany.

An outbreak of varicella among schoolchildren in Taipei

Background

The reported cases with varicella have not decreased and outbreaks of varicella among vaccinated children continue to be reported 9 years after the public vaccination program in Taipei. We investigated an outbreak to determine varicella vaccine coverage and effectiveness.

Methods

An outbreak occurred in an elementary school which located in southern Taipei from April 2007 through May 2007. A retrospect cohort study was performed by using a self-administered questionnaire for parents.

Results

Ten out of sixteen varicella cases were vaccinated. Overall vaccine coverage was 71.2%. The common reasons for not receiving varicella vaccine were that varicella vaccine was unavailable because the student didn't live in Taipei (29.4%) or the children could not be vaccinated due to certain illnesses (23.5%). The sensitivity and specificity of self-reported vaccination status was 0.900 (95% CI: 0.864, 0.935) and 0.611 (95% CI: 0.514, 0.701).

The vaccine effectiveness was 69.3%-100.0% against any disease severity of varicella. Overall vaccine effectiveness against moderate or severe varicella was 85.5%. Attending cram school was associated with the risk of developing the varicella illness (RR: 13.39; 95% CI: 5.38, 33.31). Unvaccinated students tended to show moderate to severe (>50 lesions) afflictions of the disease (RR: 4.17; 95% CI: 1.15, 15.14).

Conclusions

Because of the low vaccination coverage, varicella outbreaks continue to be reported in Taipei. Increasing vaccine coverage and second dose vaccination for increasing vaccine effectiveness may be considered.

Genotype of varicella-zoster virus isolates in South Korea

Information about the genotype of varicella-zoster virus (VZV) is useful to monitor outbreaks of vaccine strains. However, in South Korea, where varicella vaccine was introduced in 1988, there are limited data about the genotype of VZV. VZV was isolated from vesicular lesions of patients with herpes zoster or varicella in South Korea between January 2007 and June 2009. DNAs were purified from single-passage isolates. The genotype was determined by sequence analysis of open reading frame (ORF) 22. The PstI restriction enzyme site in ORF 38 and the BglI restriction enzyme site in ORF 54 were evaluated by restriction enzyme analysis. Forty-four patients with herpes zoster and nine patients with varicella were enrolled. The median age of patients with herpes zoster was 59.5 (range, 10 to 77) years, and the median age of patients with varicella was 8 (range, 6 to 9) years. In sequence analysis of ORF 22, all isolates were genotype J, irrespective of the age group. In restriction enzyme analysis, 51 of 54 (94.3%) isolates contained a PstI site in ORF 38, and all isolates contained a BglI site in ORF 54. Our data suggest that genotype J has been circulating since the 1940s in South Korea.

Varicella breakthrough infection and vaccine effectiveness in Taiwan

We performed this nationwide retrospective investigation among the recipients of varicella vaccine to evaluate the breakthrough varicella infection rate, factors associated with breakthrough infection and the vaccine effectiveness. The recipients of these vaccinations were identified through Taiwan's National Immunization Information System and data on breakthrough infections among these recipients were collected by using Taiwan's National Health Insurance Claims Database. From 2000 to 2007, 1,057,345 persons received varicella vaccinations in Taiwan. Varicella breakthrough infection occurred among 22,640 (2.1%) vaccinees and 170 (0.016%) required hospitalization for varicella disease. Annual breakthrough infection rates ranged from 0.12% to 2.04%. The mean age of vaccination was 1.6 years (median 1.3 years) and the mean age at breakthrough infection was 3.9 years. The mean interval between vaccination and the breakthrough infection was 2.3 years. The rate was significantly lower in regions where free varicella vaccinations were available than in regions where they were not (P<0.001). Varicella breakthrough infection was significantly more likely to occur at 5 and 6 years of age among the vaccinees, who received vaccination between 12 months and 23 months of age (P<0.001). The vaccine effectiveness against varicella was 82.6% and against varicella-related hospitalization was 85.4% from 2000 to 2005.

Impact of 2-dose vaccination on varicella epidemiology: Connecticut--2005-2008

In 2006, the Advisory Committee on Immunization Practices recommended that children routinely receive 2 varicella vaccine doses in place of the 1 dose previously recommended. This recommendation's initial impact on varicella epidemiology in Connecticut was assessed. Reported incidence and case-specific data were compared for 2005 and 2008. Varicella incidence decreased from 48.7 cases/100,000 persons in 2005 to 24.5 in 2008. Age-specific incidence decreased significantly (P < .05) among children aged 1-14 years. Reported varicella incidence has declined in Connecticut after implementation of routine 2-dose varicella vaccination for children. Continued surveillance is needed to determine the recommendation's full impact.

The changing epidemiology of varicella incidence after implementation of the one-dose varicella vaccination policy

The varicella vaccine has been available in the Taiwan market since July 1997. Beginning 1998-1999, Taipei City and Taichung City/County as the early launch areas included the varicella vaccine in their free pediatric vaccination programs. By contrast, the national free vaccination program was not implemented until 2004. We aim to investigate the changing epidemiology of varicella incidence through an analysis of age-period-cohort effects. With the greatest decrease in varicella incidence occurring in children aged below 6, the incidence of varicella shifted to older age groups as reflected in different birth cohorts. The current study provides important implications for the current vaccination policy.

Varicella zoster disease of the central nervous system: epidemiological, clinical, and laboratory features 10 years after the introduction of the varicella vaccine

BACKGROUND

Since the introduction of live attenuated varicella zoster virus (VZV) vaccine in 1995 there has been a significant reduction in varicella incidence and its associated complications, but the impact on VZV-associated central nervous system (CNS) disease has not been assessed.

METHODS

In this descriptive study we evaluated patients referred to the California Encephalitis Project from 1998 to 2009 with VZV PCR-positive cerebrospinal fluid (CSF). Epidemiological, clinical, and laboratory data were collected using a standardized case form. Specimens were genotyped using multi-single nucleotide polymorphism (SNP) analysis.

RESULTS

Twenty-six specimens were genotyped from patients 12-85 years of age (median, 46 years). Clinical presentations included meningitis (50%), encephalitis (42%), and acute disseminated encephalomyelitis (ADEM) (8%). Only 11 patients (42%) had a concomitant herpes zoster rash. Genotype analysis identified 20 European Group (Clade1, Clade 3) strains; 4 Asian (Clade 2) strains, and 2 Mosaic Group (Clade 4, Clade VI) strains. One specimen was recognized as vaccine strain by identifying vaccine-associated SNPs.

CONCLUSIONS

VZV continues to be associated with CNS disease, with meningitis being the most frequent clinical presentation. CNS VZV disease often presented without accompanying zoster rash. Sequencing data revealed multiple genotypes, including 1 vaccine strain detected in the CSF of a young patient with meningitis.

Assessment of varicella vaccine effectiveness in Germany: a time-series approach

A multivariate time-series regression model was developed in order to describe the 2005-2008 age-specific time-course of varicella sentinel surveillance data following the introduction of a varicella childhood vaccination programme in Germany. This ecological approach allows the assessment of vaccine effectiveness under field conditions by relating vaccine coverage in cohorts of 24-month-old children to the mean number of cases per reporting unit in the sentinel network. For the 1-2 years age group, which is directly affected by the vaccination programme, a one-dose vaccine effectiveness of 83·2% (95% CI 80·2-85·7) was estimated which corresponds to previous approaches assessing varicella vaccine effectiveness in the field in the USA.

Perspectives on vaccines against varicella-zoster virus infections

Primary infection with varicella-zoster virus (VZV) results in varicella which, in populations where immunization is not used, occurs mostly in children. Varicella is a generalized rash illness with systemic features such as fever and malaise. During varicella, VZV becomes latent in sensory ganglia of the individual, and in 70% it remains asymptomatic for their lifetime. The remaining 30% develop reactivation from latency, resulting in herpes zoster (HZ). HZ usually occurs in persons over the age of 50, and is manifested by a painful unilateral rash that usually lasts about 2 weeks and then may be followed by a chronic pain syndrome called post-herpetic neuralgia (PHN). VZV infections are notoriously more severe in immunocompromised hosts than in healthy individuals. Despite gaps in our understanding of the details of immunity to VZV, successful vaccines have been developed against both varicella and zoster.

Forecasting dengue vaccine demand in disease endemic and non-endemic countries

BACKGROUND

A dengue vaccine in large-scale clinical trials could be licensed in several years. We estimated the potential vaccine demand for different introduction strategies in 54 dengue-endemic countries and for travelers from non-endemic countries to enable vaccine producers and public health agencies to better prepare for timely utilization of the vaccine.

RESULTS

Under our assumptions, 2.4-3.5 billion dengue vaccine doses would be needed in the first five years after introduction with >75% delivered in the public sector. Among 20 potential 'early-adopter' countries, an estimated 0.9-1.4 billion doses would be needed for the same introduction approach. For the private sector, covering 10% of children and 30% of adults an estimated 443-664 million doses would be required. In non-endemic countries, travelers could use an estimated 59-89 million vaccine doses, although the present product profile would make it unlikely to be able to administer vaccine in a timely manner.

METHODS

Calculations were based on 2015-2020 population projections for endemic countries in Asia and the Americas with populations >100,000. For dengue-endemic countries we assumed country-wide routine 12-23 month-old vaccination and catch-up vaccination among 2-14 year-old children employing a 2 or 3-dose schedule. Assumptions on expected vaccination coverage were based on country-specific public, private and travelers' sectors immunization performance.

CONCLUSIONS

Our results project an upper-limit estimate of vaccine demand, with actual demand depending on country priorities, cost and product profile. Given the potential for a dengue vaccine, policymakers in endemic and nonendemic countries should consider appropriate implementation strategies in advance of licensure.

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

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

Varicella vaccination coverage of children under two years of age in Germany

Background

Since July 2004, routine varicella vaccination is recommended by the German Standing Vaccination Committee in Germany. Health Insurance Funds started to cover vaccination costs at different time points between 2004 and 2006 in the Federal States. Nationwide representative data on vaccination coverage against varicella of children under two years of age are not available. We aimed to determine varicella vaccination coverage in statutory health insured children under two years of age in twelve German Federal States using data from associations of statutory health insurance physicians (ASHIPs), in order to investigate the acceptance of the recommended routine varicella vaccination programme.

Methods

We analysed data on varicella vaccination from 13 of 17 ASHIPs of the years 2004 to 2007. The study population consisted of all statutory health insured children under two years of age born in 2004 (cohort 2004) or 2005 (cohort 2005) in one of the studied regions. Vaccination coverage was determined by the number of children vaccinated under 2 years of age within the study population.

Results

Varicella vaccination coverage of children under two years of age with either one dose of the monovalent varicella vaccine or two doses of the measles, mumps, rubella, and varicella vaccine increased from 34% (cohort 2004) to 51% (cohort 2005) in the studied regions (p < 0.001). More than half of the vaccinated children of cohort 2004 and two third of cohort 2005 were immunised at the recommended age 11 to 14 months. The level of vaccination coverage of cohort 2004 was significantly associated with the delay in introduction of cost coverage since the recommendation of varicella vaccination (p < 0.001).

Conclusions

Our study shows increasing varicella vaccination coverage of young children, indicating a growing acceptance of the routine varicella vaccination programme by the parents and physicians. We recommend further monitoring of vaccination coverage using data from ASHIPs to investigate acceptance of the routine vaccination programmes over time.

Incremental effectiveness of second dose varicella vaccination for outbreak control at an elementary school in Philadelphia, pennsylvania, 2006

BACKGROUND

In 2006, the Philadelphia Department of Public Health conducted an investigation of a varicella outbreak at an elementary school in which second-dose vaccination for outbreak control (VOC) was implemented. We evaluated the effectiveness of this intervention.

METHODS

Self-administered questionnaires collected varicella disease and vaccination information. Students eligible for second-dose VOC were 1-dose vaccine recipients without prior varicella disease. A breakthrough varicella case was defined as a maculopapulovesicular rash in a student with onset >42 days after 1-dose vaccination without other apparent cause. Vaccine effectiveness was evaluated using survival analysis techniques and analyzed by vaccine status (first dose versus second dose). Multivariable Cox proportional hazard models were used to identify statistical interactions and adjust for confounders.

RESULTS

The questionnaire response rate was 92% (342/370). Of the 286 eligible students, 187 (65%) received a second-dose VOC. The crude attack rate was 9/187 (5%) among second-dose VOC recipients; 43/99 (43%) among 1-dose recipients, and 5/6 (83%) among unvaccinated students. Second-dose VOC recipients had milder rashes, compared with 1-dose or unvaccinated students. The adjusted incremental second-dose vaccine effectiveness was 76% (95% confidence interval: 44%-90%) for students with classroom exposure. Incremental effectiveness was similar (79%) when we extended the immune response time from 4 days to 7 days after second-dose VOC.

CONCLUSIONS

Second-dose VOC resulted in a substantial reduction in varicella incidence for students with classroom exposure. Until high rates of routine second-dose vaccine coverage are achieved, clinicians should consider second-dose VOC an appropriate intervention to reduce disease transmission in institution-based outbreaks.

Genome-wide mutagenesis reveals that ORF7 is a novel VZV skin-tropic factor

The Varicella Zoster Virus (VZV) is a ubiquitous human alpha-herpesvirus that is the causative agent of chicken pox and shingles. Although an attenuated VZV vaccine (v-Oka) has been widely used in children in the United States, chicken pox outbreaks are still seen, and the shingles vaccine only reduces the risk of shingles by 50%. Therefore, VZV still remains an important public health concern. Knowledge of VZV replication and pathogenesis remains limited due to its highly cell-associated nature in cultured cells, the difficulty of generating recombinant viruses, and VZV's almost exclusive tropism for human cells and tissues. In order to circumvent these hurdles, we cloned the entire VZV (p-Oka) genome into a bacterial artificial chromosome that included a dual-reporter system (GFP and luciferase reporter genes). We used PCR-based mutagenesis and the homologous recombination system in the E. coli to individually delete each of the genome's 70 unique ORFs. The collection of viral mutants obtained was systematically examined both in MeWo cells and in cultured human fetal skin organ samples. We use our genome-wide deletion library to provide novel functional annotations to 51% of the VZV proteome. We found 44 out of 70 VZV ORFs to be essential for viral replication. Among the 26 non-essential ORF deletion mutants, eight have discernable growth defects in MeWo. Interestingly, four ORFs were found to be required for viral replication in skin organ cultures, but not in MeWo cells, suggesting their potential roles as skin tropism factors. One of the genes (ORF7) has never been described as a skin tropic factor. The global profiling of the VZV genome gives further insights into the replication and pathogenesis of this virus, which can lead to improved prevention and therapy of chicken pox and shingles.

The Varicella Zoster Virus (VZV) is the causative agent of chicken pox and shingles. The long-term efficacy of the current chickenpox vaccine is yet to be determined, and the current shingles vaccine fails to provide protective immunity for a substantial number of individuals. Shingles can also lead to post-herpetic neuralgia (PHN), a debilitating condition associated with an intractable pain that can linger for life. Therefore, VZV remains an important public health concern. We use growth-rate analysis of our genome-wide deletion library to determine the essentiality of all known VZV genes, including novel annotations for 51% of the VZV proteome. We also discovered a novel skin-tropic factor encoded by ORF7. Overall, our identification of genes essential for VZV replication and pathogenesis will serve as the basis for multiple in-depth genetic studies of VZV, which can lead to improved prevention and therapy of chicken pox and shingles. For example, essential genes may be appealing drug targets and genes whose deletion causes a substantial growth defect may be prospective candidates for novel live attenuated vaccines.

Seroprevalence rate after one dose of varicella vaccine in infants

SUMMARY BACKGROUND

Live, attenuated varicella vaccine has been used since 1988 in Korea. However, varicella is still prevalent among both vaccinated and unvaccinated individuals, despite a relatively high level of immunization rate up to 80%. A recent report has demonstrated approximately 20% of primary vaccine failure rate after one dose of varicella vaccine using the fluorescent antibody to membrane antigen (FAMA) assay.

METHODS

The seroprevalence rate was determined using the FAMA and ELISA assays in 67 Korean infants following one dose of varicella vaccine. Positive fluorescence at a serum dilution of 1:4 or greater was considered as seropositive.

RESULTS

The median age at vaccination was 12 months and the post-immunization sera were obtained on average 6.3 months (range 6 weeks-12 months) after vaccination. Among the 67 vaccinated infants, 56 (83.6%) were seropositive by FAMA assay while 30 (44.8%) were seropositive by ELISA. The geometric mean titers (GMTs) of the seropositive vaccinated infants (n = 56) were significantly lower than the GMTs of 9 individuals with a history of varicella (1:17.0 vs. 1:74.7, P = 0.001). Although there were no significant differences in seropositive rates according to intervals, there was a decreasing trend in the GMTs over time among the 56 seropositive recipients (r(2) = 0.154, P < 0.001).

CONCLUSIONS

These data can be useful for optimizing the immunization strategy against varicella and should be confirmed by a prospective study including a large number of immunized infants.