An outbreak of varicella in elementary school children with two-dose varicella vaccine recipients--Arkansas, 2006

Analysis of the reliability of rapid diagnostic tests for varicella, including breakthrough cases

In the era of universal varicella vaccination, diagnosis of varicella is challenging, especially for breakthrough cases. We sought to clarify the reliability of direct varicella-zoster virus (VZV) loop-mediated isothermal amplification (LAMP) and DermaQuick® VZV using the immunochromatography technique as rapid diagnostic tests for varicella. In addition, the usefulness of saliva as a sample type for direct LAMP was investigated. Among the 46 enrolled patients with suspected VZV infection, 31 patients (67.3%) were positive for the nucleic acid test based on real-time PCR from skin swab samples. Direct LAMP of skin swabs was positive in 29 (63.0%) of 46 patients. DermaQuick® VZV was positive in 25 (54.3%) of 46 patients. VZV DNA was detected in only 48.4% of oral swabs with the direct LAMP method. With real-time polymerase chain reaction (PCR) as the standard for diagnosing varicella, the sensitivity and specificity of DermaQuick® VZV were 80.7% and 100%, respectively. The sensitivity and specificity of direct LAMP from skin swabs were 93.6% and 100%, respectively. The sensitivity and specificity of real-time PCR for DNA extracted from oral swabs were 74.2% and 93.3%, respectively. Thus, oral swab samples are not suitable for breakthrough varicella diagnosis. Although DermaQuick® VZV is considered the most convenient point-of-care test for varicella, its sensitivity and specificity were lower than those of direct VZV LAMP.

Evaluation of varicella vaccine effectiveness during outbreaks in schools or nurseries by cross-sectional study

OBJECTIVE

The aim of this study was to elucidate vaccine effectiveness (VE) during varicella outbreaks in schools and nurseries in Japan.

METHODS

An outbreak was defined as emergence of three or more cases of varicella within 21 days at the same institute. Clinical information such as varicella vaccination status, and history of varicella was collected. If a child had varicella during the outbreak, information about absences, fever, and disease severity was collected.

RESULTS

From September 2018 to January 2020, four outbreaks were reported around our institute from three elementary schools and one nursery. A total of 676 children were analyzed in this study. Seventy-six children (11.2%) were unvaccinated, 309 (45.7%) had received one dose of vaccine, and 291 (43.0%) had received two doses. Most children in Pre-K2 (1-2 years old) to Pre-K6 (5-6 years old), who were the targets of the national immunization schedule, received two doses. Meanwhile, most children older than third grade received single dose. Seventy-five children (11.1%) had varicella. Varicella prevalence from Pre-K5 to the third grade was greater than 10%. The adjusted VEs of single- and two-dose of varicella vaccine were 57.8% and 89.0%. The number of days absent was significantly longer in unvaccinated children than single-dose recipients (P = 0.0145). Unvaccinated children had significantly more severe skin eruptions than single-dose recipients (P = 0.0046) and two-dose recipients (P = 0.0258).

CONCLUSIONS

Although VEs of single-dose varicella vaccination during outbreaks was not high, the VE of two-dose vaccination was similar to that in a previously reported case-control study.

Trend in varicella patients 4 years after implementation of universal two-dose varicella vaccination in Japan

OBJECTIVE

To elucidate the trend and clinical spectrum of virologically diagnosed varicella patients after implementation of universal vaccination as a national immunization program in Japan.

PATIENTS AND METHODS

Study subjects were patients suspected of varicella, less than 15 years of age, who visited 14 pediatric clinics in the Nagoya VZV Study Group from September 2015 to August 2019. Practitioners collected patient samples and information such as backgrounds, clinical symptoms, and previous immunization status. All patients were confirmed as having varicella based on molecular diagnostic assays.

RESULTS

Varicella zoster virus (VZV) DNA was detected in swab samples from 506 (83.1%) of the 609 suspected patients. The 455 varicella patients for whom vaccination status was available were divided into two groups: 180 universal vaccination targets and 275 non-targets. Numbers of monthly varicella patients decreased gradually during the observation period. In the 2016/17 season, the seasonal epidemic of varicella became undetectable in the universal vaccination target group, and starting in the 2017/18 season, it was obscured even in the non-target group. The median age of patients was significantly lower in the universal vaccination target group (3 years) than the non-target group (7 years) (P < 0.001). Vaccination status differed significantly between the two groups (P < 0.001). Most varicella patients were in the non-target group, especially those who had been vaccinated once (60.4%). Frequency of fever (P < 0.001) and number of skin rashes at the time of the first hospital visit (P = 0.001) were significantly higher in the non-target group.

CONCLUSIONS

Although the number of childhood varicella patients declined after implementation of national immunization with two doses of varicella vaccination, sporadic outbreaks still occurred, mainly in the non-universal vaccination target group. Insufficient vaccination of members of this group is likely to be a major reason for small local outbreaks.

Clinical characteristics and risk factors associated with breakthrough varicella during varicella outbreaks

BACKGROUND

Although a varicella vaccine has been available in China since 1998 in the private sector, varicella outbreaks and breakthrough varicella (BV) still occur. In 2018, four varicella outbreaks with high BV rate sequentially occurred in four schools in Lu'an, sparking local public health authority's concerns on the varicella vaccine. Therefore, we conducted this investigation to evaluate varicella vaccine effectiveness (VE), characterize BV, and detect potential risk factors associated with BV.

METHODS

This was a three-stage study. First, a retrospective cohort study was done in each school to estimate the VEs of varicella vaccine  during outbreaks. Second, a descriptive epidemiological method was used to describe the characteristics of the four outbreaks and to compare the clinical characteristics between the BV cases and unvaccinated varicella cases. To identify the risk factors associated with BV, we conducted an unmatched case-control study in the third stage of the study.

RESULTS

A total of 199 cases were identified among four outbreaks, and the overall attack rate was 14%. Of 1203 students with available vaccination information, 822 (68%) were vaccinated at least once. The overall VEs among four outbreaks ranged from 19% to 69%, whereas the VE against moderate or severe varicella ranged from 74% to 90%. Compared with unvaccinated varicella cases, the moderate or severe varicella (p < .001) and fever (p = .029) in the BV group were less common. Besides, BV cases had a shorter duration of disease (p = .007). Children vaccinated more than six years before the outbreak had a higher risk of developing BV compared with those vaccinated within the past six years (OR = 2.4, 95% CI: 1.2-4.8). The risk of developing BV differed by the exposure intensity. Compared with the presence of three or fewer varicella cases in the same class, the OR was 7.8 (95% CI: 3.6-16.9) for four to nine cases in the same class and 25.2 (95% CI: 13.5 -47.2) for that of 10 or more cases.

CONCLUSIONS

The overall VE was insufficient to protect varicella infection, and the VE for moderate or severe varicella was only moderate. The manifestations of BV cases were generally milder than those seen in natural varicella infection. The time since vaccination and the intensity of exposure are risk factors for developing BV during an outbreak.

Reliability of direct varicella zoster virus loop-mediated isothermal amplification method for rapid diagnosis of breakthrough varicella

BACKGROUND

Since patients with breakthrough varicella (BV) have mild symptoms, clinical diagnosis is difficult. In high vaccine coverage area, as BV occurs sporadically, point of care test is required for controlling varicella outbreak. In this study, the reliability of varicella zoster virus (VZV)-loop mediated isothermal amplification (LAMP) was evaluated for the rapid diagnosis of BV.

STUDY DESIGN

A total of 328 swab samples collected from patients with suspected varicella were analyzed. For the laboratory diagnosis of varicella, VZV real-time PCR was carried out using DNA extracted from swab samples. Swab samples without DNA extraction were used for VZV-LAMP(direct-LAMP).

RESULTS

VZV infection was diagnosed by real-time PCR in 285 cases, including 105 natural varicella cases and 180 BV cases. VZV DNA was detected in 250 (87.8%) of the 285 cases by direct-LAMP. The presence and duration of fever, number of skin eruptions, and VZV DNA load were significantly lower in BV than natural varicella. The sensitivity of direct-LAMP for the diagnosis of varicella and BV was 93.3% and 84.4%, respectively.

CONCLUSIONS

Direct LAMP was considered to be useful for rapid diagnosis of BV as it has several advantages such as low cost, ease and rapidity, as compared to real time PCR.

Effectiveness of post-exposure prophylaxis during varicella outbreaks among primary and middle school students in Shanghai: An analysis of three-year surveillance data

OBJECTIVES

To evaluate the effectiveness of post-exposure prophylaxis conducted during varicella outbreaks among students in Shanghai.

METHODS

Surveillance data were collected from September 1, 2013 to December 31, 2016 involving 3524 susceptible students in 109 primary and middle school classes where emergency vaccinations (EVs) had been administered. Students were divided into two groups according to their prior vaccination (PV) varicella vaccine status. A secondary attack rate was used to compare EV and non-EV groups using a chi-squared test. Stratification analyses were performed, adjusting for the EV administration date, the vaccination coverage rate, and the number of cases prior to the EV.

RESULTS

The effectiveness rate was 92.2% (95% confidence interval (CI): 37.1-99.0%) when EV was applied within 3 days following the outbreak onset date, and 95.2% (95% CI: 79.9-98.8%) when vaccination coverage was ≥80% among students with PV. When students with PV received an EV for varicella within 3 days, the effectiveness rate was 100%.

CONCLUSIONS

EV showed high protective effectiveness for varicella during outbreaks, especially if administered within 3 days of an outbreak and in conjunction with a high coverage rate.

Varicella outbreak in a highly-vaccinated school population in Beijing, China during the voluntary two-dose era

BACKGROUND

Two-dose varicella vaccination has been available in Beijing since 2012 in the private sector. We investigated a varicella outbreak in a highly vaccinated elementary school population.

METHODS

A cohort study was carried out and a varicella case was defined as an acute onset of generalized maculopapulovesicular rash without other apparent cause in a student attending the school from March 29 through May 17, 2015. Breakthrough varicella was defined as varicella >42days after the last vaccine dose among both 1- or 2-dose varicella vaccine recipients. Vaccination information was collected from immunization records; information on prior varicella and clinical presentations was collected by surveying students' parents.

RESULTS

Of the 1056 students in the school, 1027 (97.3%) reported no history of varicella. Prior to the outbreak, 98.6% of students had received ≥1 dose of varicella vaccine, and most (63.2%) students received two doses. Twenty varicella cases were identified for an overall attack rate of 2.0%. Half of the cases occurred in the classroom of the index case-patient, a two-dose recipient who was not isolated after symptom onset. Breakthrough varicella accounted for 95% of cases (19/20) with attack rates of 14.3% (1/7), 1.6% (6/362) and 2.0% (13/649) among unvaccinated, one-dose, and two-dose students, respectively. Most case-patients (18/20, 90%) had <50 lesions. No difference in clinical presentations was found between one-dose and two-dose recipients with breakthrough varicella.

CONCLUSION

Moderate two-dose varicella vaccine coverage was insufficient to prevent a varicella outbreak. Two-dose recipients with breakthrough varicella are contagious. High two-dose varicella vaccine coverage and timely isolation of cases may be needed for varicella outbreak prevention in the two-dose era.

Laboratory Diagnosis of Breakthrough Varicella in Children

BACKGROUND

Breakthrough varicella (BV) develops in vaccinated persons as a result of infection by wild-type varicella-zoster virus more than 42 days after varicella vaccination. The clinical symptoms are atypical, and clinical diagnosis can be difficult. We investigated laboratory-based diagnostic methods that are relatively simple and highly precise to conduct accurate surveillance.

SUBJECTS AND METHODS

We enrolled 42 patients with suspected BV at 2 pediatric hospitals and performed a real-time polymerase chain reaction (PCR) on the skin lesions to confirm the BV diagnosis. We performed PCR on saliva and blood collected during the acute phase, as well as direct fluorescent antibody (DFA) imaging on lesions, and measured varicella-zoster virus immunoglobulin (Ig) G and IgM during the acute and convalescent phases.

RESULTS

We confirmed the BV diagnosis in 31 of 42 enrolled patients. The sensitivity of DFA imaging of the lesion, and PCR of saliva and blood were 93.5%, 87.1% and 61.3%, respectively. IgM was detected in 12.9% of patients during the acute phase and in 65.5% during the convalescent phase. IgG increased more than 4-fold in 86.2% of patients between the acute and convalescent phases. The sensitivity and specificity of the assay were 83.9% and 81.8%, respectively, when the diagnostic criteria for IgG were set to greater than 20 during the acute phase.

CONCLUSIONS

The gold standard of laboratory-based diagnosis of BV has been the PCR of samples taken from lesions. However, DFA of the lesion showed equivalent sensitivity when compared with PCR. PCR using saliva samples is an effective, noninvasive method of diagnosis. We found that high values of IgG during the acute phase can aid in the diagnosis of BV.

Varicella seroepidemiology in United States air force recruits: A retrospective cohort study comparing immunogenicity of varicella vaccination and natural infection

BACKGROUND/OBJECTIVES

Infection with varicella zoster virus (VZV) produces lifelong immunity, but duration of post-vaccination immunity has not been established. The purpose of this study is to determine if a difference exists in the long-term seropositivity of anti-VZV antibodies in a cohort of young adults who were vaccinated against varicella as compared to a similar cohort with a history of chickenpox disease, and to determine which variables best predict waning seropositivity following varicella vaccination.

METHODS

This retrospective cohort study captures immunization and serology data from approximately 10,000 recruits who entered basic military training between January 1, 2008, and December 31, 2015, and who have childhood immunization records in the Air Force Aeromedical Services Information Management System. Varicella vaccine immunogenicity was determined relative to the immunogenicity of chickenpox disease, as measured by multiplex flow immunoassay. Among vaccine recipients, waning seroimmunity was modeled and adjusted for several important covariates.

RESULTS

Basic military trainees who received varicella vaccine in childhood were 24% less likely to be seropositive to VZV than trainees who were exempt from vaccine due to a history of chickenpox disease. There was no significant difference in seropositivity between male and female trainees. The odds of a vaccinated trainee being seropositive to VZV decreased by 8% with each year elapsed since vaccination. Seroprevalence declined below estimated herd immunity thresholds in vaccinated trainees born after 1994, and in the cohort as a whole for trainees born after 1995.

CONCLUSION

Despite prior vaccination, seroimmunity in a large cohort of young adults unexposed to wild-type VZV failed to meet the estimated threshold for herd immunity. If vaccination in accordance with the current US VZV vaccination schedule is inadequate to maintain herd immunity, young adults not previously exposed to wild-type VZV may be at increased risk for varicella outbreaks.

Varicella Vaccine Effectiveness in Preventing Community Transmission in the 2-Dose Era

OBJECTIVES

We examined overall and incremental effectiveness of 2-dose varicella vaccination in preventing community transmission of varicella among children aged 4 to 18 years in 2 active surveillance sites. One-dose varicella vaccine effectiveness (VE) was examined in those aged 1 to 18 years.

METHODS

From May 2009 through June 2011, varicella cases identified during active surveillance in Antelope Valley, CA and Philadelphia, PA were enrolled into a matched case-control study. Matched controls within 2 years of the patient's age were selected from immunization registries. A standardized questionnaire was administered to participants' parents, and varicella vaccination history was obtained from health care provider, immunization registry, or parent records. We used conditional logistic regression to estimate varicella VE against clinically diagnosed and laboratory-confirmed varicella.

RESULTS

A total of 125 clinically diagnosed varicella cases and 408 matched controls were enrolled. Twenty-nine cases were laboratory confirmed. One-dose VE (1-dose versus unvaccinated) was 75.6% (95% confidence interval [CI], 38.7%-90.3%) in preventing any clinically diagnosed varicella and 78.1% (95% CI, 12.7%-94.5%) against moderate or severe, clinically diagnosed disease (≥50 lesions). Among subjects aged ≥4 years, 2-dose VE (2-dose versus unvaccinated) was 93.6% (95% CI, 75.6%-98.3%) against any varicella and 97.9% (95% CI, 83.0%-99.7%) against moderate or severe varicella. Incremental effectiveness (2-dose versus 1-dose) was 87.5% against clinically diagnosed varicella and 97.3% against laboratory-confirmed varicella.

CONCLUSIONS

Two-dose varicella vaccination offered better protection against varicella from community transmission among school-aged children compared with 1-dose vaccination.

Global Varicella Vaccine Effectiveness: A Meta-analysis

CONTEXT

Several varicella vaccines are available worldwide. Countries with a varicella vaccination program use 1- or 2-dose schedules.

OBJECTIVE

We examined postlicensure estimates of varicella vaccine effectiveness (VE) among healthy children.

DATA SOURCES

Systematic review and descriptive and meta-analysis of Medline, Embase, Cochrane libraries, and CINAHL databases for reports published during 1995-2014.

STUDY SELECTION

Publications that reported original data on dose-specific varicella VE among immunocompetent children.

DATA EXTRACTION

We used random effects meta-analysis models to obtain pooled one dose VE estimates by disease severity (all varicella and moderate/severe varicella). Within each severity category, we assessed pooled VE by vaccine and by study design. We used descriptive statistics to summarize 1-dose VE against severe disease. For 2-dose VE, we calculated pooled estimates against all varicella and by study design.

RESULTS

The pooled 1-dose VE was 81% (95% confidence interval [CI]: 78%-84%) against all varicella and 98% (95% CI: 97%-99%) against moderate/severe varicella with no significant association between VE and vaccine type or study design (P > .1). For 1 dose, median VE for prevention of severe disease was 100% (mean = 99.4%). The pooled 2-dose VE against all varicella was 92% (95% CI: 88%-95%), with similar estimates by study design.

LIMITATIONS

VE was assessed primarily during outbreak investigations and using clinically diagnosed varicella.

CONCLUSIONS

One dose of varicella vaccine was moderately effective in preventing all varicella and highly effective in preventing moderate/severe varicella, with no differences by vaccine. The second dose adds improved protection against all varicella.

Impact of the US Two-dose Varicella Vaccination Program on the Epidemiology of Varicella Outbreaks: Data from Nine States, 2005-2012

BACKGROUND

A routine 2-dose varicella vaccination program was adopted in 2007 in the US to help further decrease varicella disease and prevent varicella outbreaks. We describe trends and characteristics of varicella outbreaks reported to the Centers for Disease Control and Prevention (CDC) during 2005-2012 from 9 states.

METHODS

Data on varicella outbreaks collected by 9 state health departments were submitted to CDC using the CDC outbreak reporting worksheet. Information was collected on dates of the outbreak, outbreak setting and number of cases by outbreak; aggregate data were provided on the numbers of outbreak-related cases by age group, vaccination status and laboratory confirmation.

RESULTS

Nine hundred and twenty-nine outbreaks were reported from the 6 states, which provided data for each year during 2005-2012. Based on data from these 6 states, the number of outbreaks declined by 78%, decreasing from 147 in 2005 to 33 outbreaks in 2012 (P = 0.0001). There were a total of 1015 varicella outbreaks involving 13,595 cases reported by the 9 states from 2005 to 2012. The size and duration of outbreaks declined significantly over time (P < 0.001). The median size of outbreaks was 12, 9 and 7 cases and median duration of outbreaks was 38, 35 and 26 days during 2005-2006, 2007-2009 and 2010-2012, respectively. Majority of outbreaks (95%) were reported from schools, declining from 97% in 2005-2006 to 89% in 2010-2012. Sixty-five percent of outbreak-related cases occurred among 5-year to 9-year olds, with the proportion declining from 76% in 2005-2006 to 45% during 2010-2012.

CONCLUSIONS

The routine 2-dose varicella vaccination program appears to have significantly reduced the number, size and duration of varicella outbreaks in the US.

Two-dose varicella vaccine effectiveness and rash severity in outbreaks of varicella among public school students

BACKGROUND

Universal 2-dose varicella vaccination was recommended in 2006 to further reduce varicella disease burden. This study examined 2-dose varicella vaccine effectiveness (VE) and rash severity in the setting of school-associated varicella outbreaks.

METHODS

A case control study was conducted from January 2010 to May 2011 in all West Virginia public schools. Clinically diagnosed cases from varicella outbreaks were matched with classmate controls. Vaccination information was collected from school, health department and healthcare provider immunization information systems.

RESULTS

Among the 133 cases and 365 controls enrolled, VE against all varicella was 83.2% [95% confidence interval (CI): 69.2%-90.8%] for 1-dose of varicella vaccine and 93.9% (95% CI: 86.9%-97.1%) for 2-dose; the incremental VE (2-dose vs. 1-dose) was 63.6% (95% CI: 32.6%-80.3%). In preventing moderate/severe varicella, 1-dose varicella vaccine was 88.2% (95% CI: 72.7%- 94.9%) effective, and 2-dose vaccination was 97.5% (95% CI: 91.6%-99.2%) effective, with the incremental VE of 78.6% (95% CI: 40.9%-92.3%). One-dose VE declined along with time since vaccination (VE = 93.0%, 88.0% and 81.8% in <5, 5-9 and ≥ 10 years after vaccination, P = 0.001 for trend). Both 1- and 2-dose breakthrough cases had milder rash than unvaccinated cases (<50 lesion: 24.6%, 49.1% and 70.0% in unvaccinated, 1-dose and 2-dose cases, P < 0.001), and no severe disease was found in 2-dose cases.

CONCLUSIONS

Two-dose varicella vaccination is highly effective and confers higher protection than a 1-dose regimen. High 2-dose varicella vaccination coverage should maximize the benefits of the varicella vaccination program and further reduce varicella disease burden in the United States.

Vaccination to prevent varicella: Goldman and King's response to Myers' interpretation of Varicella Active Surveillance Project data

BACKGROUND

There is increasing evidence that herpes zoster (HZ) incidence rates among children and adults (aged <60 years) with a history of natural varicella are influenced primarily by the frequency of exogenous exposures, while asymptomatic endogenous reactivations help to cap the rate at approximately 550 cases/100,000 person-years when exogenous boosting becomes rare. The Antelope Valley Varicella Active Surveillance Project was funded by the Centers for Disease Control and Prevention in 1995 to monitor the effects of varicella vaccination in one of the three representative regions of the United States. The stability in the data collection and number of reporting sites under varicella surveillance from 1995-2002 and HZ surveillance during 2000-2001 and 2006-2007 contributed to the robustness of the discerned trends.

DISCUSSION

Varicella vaccination may be useful for leukemic children; however, the target population in the United States is all children. Since the varicella vaccine inoculates its recipients with live, attenuated varicella-zoster virus (VZV), clinical varicella cases have dramatically declined. Declining exogenous exposures (boosts) from children shedding natural VZV have caused waning cell-mediated immunity. Thus, the protection provided by varicella vaccination is neither lifelong nor complete. Moreover, dramatic increases in the incidence of adult shingles cases have been observed since HZ was added to the surveillance in 2000. In 2013, this topic is still debated and remains controversial in the United States.

SUMMARY

When the costs of the booster dose for varicella and the increased shingles recurrences are included, the universal varicella vaccination program is neither effective nor cost-effective.

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.

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.

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.

Knowledge, attitudes, and practices for diagnosing breakthrough varicella in the outpatient setting

OBJECTIVES

We assessed provider knowledge, attitudes, and practices for the management of breakthrough varicella and identified barriers to implementation of laboratory testing and reporting.

METHODS

We surveyed 145 health-care providers (HCPs) from 30 pediatric practices in Philadelphia who did not have a history of laboratory testing for breakthrough varicella. The self-administered survey instrument collected information on clinicians' practices for management of children presenting with rash, infection-control strategies, reporting to public health agencies, and laboratory testing.

RESULTS

Among the 144 HCPs who completed the survey, 73 (51%) had practiced for more than 10 years. While 115 HCPs (80%) would elect to evaluate a child with rash in the office, only 19 (13%) would submit diagnostics. When patients had a known recent exposure to varicella, 84 HCPs (58%) would use laboratory tests: 40% would use direct fluorescent antibody staining on a specimen from a cutaneous lesion, 24% would use polymerase chain reaction on a lesion specimen, 21% would use acute and convalescent serology, and 10% would use other tests. While waiting for test results, 82 HCPs (57%) would advise that the child be kept at home, 39 (27%) would notify the local health department, and 33 (23%) would inform the school nurse.

CONCLUSION

As varicella becomes increasingly uncommon, laboratory confirmation becomes more critical for appropriate diagnosis, similar to poliomyelitis and measles. Our findings suggest that HCPs need further education regarding laboratory confirmation, containment, and reporting 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.

Vaccine effectiveness evaluation during a varicella outbreak among children of primary schools and day-care centers in a region which adopted UMV

This study describes an outbreak of varicella, in a small town in the region of Puglia, Southern Italy, in the period between February-March 2011. This outbreak presented the opportunity to assess varicella vaccine effectiveness and its determinants. The outbreak occurred in a small community in Puglia; parents of the children attending the schools of the community were contacted by telephone and information was gathered on current disease and varicella history. Varicella vaccination history was verified through the immunization registry of the Local Health Unit. Before the outbreak, immunization coverage was 86.6% of children attending preschool and 51.9% of children attending elementary school. In day care center where the outbreak was happened, the attack rate in vaccinated individuals was 32.1% and 80% in susceptible unvaccinated individuals. VE is therefore estimated as 59.9% (95% CI = 48.3-69.8). In the elementary school the VE can be calculated as 69.2% (95% CI = 50.5-88.1), since the attack rate in unvaccinated children was of 23.1% and in vaccinated of 7.1. The time between vaccination and the onset of the epidemic appears higher in children with a vaccine failure. The results of this study highlight the need for a reflection on the desirability of adopting a shorter schedule in Italy, with a minimum 1 mo interval between MMRV doses.

Challenges in confirming a varicella outbreak in the two-dose vaccine era

BACKGROUND

A second dose of varicella vaccine was recommended for U.S. children in 2006. We investigated a suspected varicella outbreak in School District X, Texas to determine 2-dose varicella vaccine effectiveness (VE).

METHODS

A varicella case was defined as an illness with maculopapulovesicular rash without other explanation with onset during April 1-June 10, 2011, in a School District X student. We conducted a retrospective cohort in the two schools with the majority of cases. Lesion, saliva, and environmental specimens were collected for varicella-zoster virus (VZV) PCR testing. VE was calculated using historic attack rates among unvaccinated.

RESULTS

In School District X, 82 varicella cases were reported, including 60 from Schools A and B. All cases were mild, with a median of 14 lesions. All 10 clinical specimens and 58 environmental samples tested negative for VZV. Two-dose varicella vaccination coverage was 66.4% in Schools A and B. Varicella VE in affected classrooms was 80.9% (95% CI: 67.2-88.9) among 1-dose vaccinees and 94.7% (95% CI: 89.2-97.4) among 2-dose vaccinees in School A, with a second dose incremental VE of 72.1% (95% CI: 39.0-87.3). Varicella VE among School B students did not differ significantly by dose (80.1% vs. 84.2% among 1-dose and 2-dose vaccinees, respectively).

CONCLUSION

Laboratory testing could not confirm varicella as the etiology of this outbreak; clinical and epidemiologic data suggests varicella as the likely cause. Better diagnostics are needed for diagnosis of varicella in vaccinated individuals so that appropriate outbreak control measures can be implemented.

Waning immunity to varicella in infants of human immunodeficiency virus-seropositive and -seronegative mothers

Immunity to varicella in HIV-exposed and -unexposed infants born to unvaccinated mothers, acquiring protective antibodies at birth declined to nonprotective (<1:8) levels by 5 months of age. Therefore, infants become susceptible to varicella before 12 months, which is the recommended time for varicella immunizations in the United States. Vaccination of susceptible HIV-seronegative women in the postpartum period may be important to consider.

Second-dose varicella vaccination coverage in children and adolescents in a managed care organization in California, 2006-2009

We assessed trends of second-dose varicella-containing vaccine coverage among children and adolescents in Kaiser Permanente Southern California health plan since the Advisory Committee on Immunization Practices recommendation of 2-dose varicella vaccination in 2006. The overall second-dose coverage increased rapidly from 42.1% in 2007 to 74.6% in 2009. The increasing trend was observed in all strata defined by age and race/ethnicity, with the highest coverage among children aged 5 to 6 years old. However, non-Hispanic White race/ethnicity and living in a neighborhood with higher education level were inversely associated with the second-dose uptake.

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.

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.

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.

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.

Decline in varicella-related ambulatory visits and hospitalizations in the United States since routine immunization against varicella

BACKGROUND

Widespread varicella vaccination has led to substantial decreases in varicella-related mortality and hospitalizations. The effect of the vaccine on ambulatory care utilization is poorly defined.

OBJECTIVE

To determine trends in varicella-related ambulatory care and hospital discharges before and after vaccine licensure.

DESIGN, SETTING, AND PARTICIPANTS

Estimates of varicella-related ambulatory and hospital discharges were calculated for the pre- (1993-1995) and post- (1996-2004) vaccine licensure periods using the National Ambulatory Medical Care Survey, National Hospital Ambulatory Medical Care Survey, and National Hospital Discharge Survey.

MAIN OUTCOME MEASURE

Ambulatory and hospital discharge rates for varicella.

RESULTS

The rate of varicella-related ambulatory discharges decreased by 66% from 106.6 per 100,000 (95% confidence interval [CI]: 80.5-132.6) in the prelicensure period to 36.4 per 100,000 population (95% CI: 29.3-43.5) in the post-licensure period (P < 0.001). The decrease was significant across all age groups <45 years, with the greatest reduction (98%) occurring among patients 0 to 4 years of age. The incidence of varicella-related hospital discharges decreased by 53% from 30.9 per 100,000 (95% CI: 24.4-37.3) to 14.5 per 100,000 population (95% CI: 12.1-16.8; P < 0.001). This difference was significant among patients <14 years of age. Rates of varicella-related ambulatory discharges decreased significantly for both whites and non-whites in the postlicensure period, but postlicensure ambulatory discharge rates remained higher for non-whites than for whites. Decreases in varicella-related hospital discharges were statistically significant for whites and non-whites. Racial differences in the incidence of varicella-related hospital discharges also persisted following vaccine licensure.

CONCLUSIONS

Varicella-related ambulatory visits and hospitalizations have decreased significantly in the period after licensure of the varicella vaccine.