Varicella breakthrough infection and vaccine effectiveness in Taiwan

Breakthrough SARS-CoV-2 infections after vaccination: a critical review

At the beginning of the current pandemic, it was believed that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection would induce lifelong immunity and that reinfections would be unlikely. However, after several cases of reinfection were documented in previously infected patients, this was understood to be a false assumption, and this waning humoral immunity has raised significant concerns. Accordingly, long-term and durable vaccine-induced antibody protection against infection have also become a challenge, as several breakthroughs of COVID-19 infection have been identified in individuals who were fully vaccinated. This review discusses the current evidence on breakthrough COVID-19 infections occurring after vaccination.

Seroprevalence of Varicella-Zoster Virus and Measles among Healthcare Workers in a Tertiary Medical Center in Korea

Measles and varicella still occur in the general population despite the widespread vaccination against them, and healthcare workers (HCWs) are still at risk of exposure to these diseases. Here, we evaluated the seroprevalence of measles and varicella-zoster virus (VZV) in HCWs and the trend of seroprevalence according to age, birth year, and occupational group. The serostatuses of measles and VZV of HCWs during new employee medical examinations between October 2015 and October 2021 were included. Thereafter, the trends of seroprevalence according to age, birth year, and occupational groups were evaluated. Overall, 2070 and 1827 HCWs were evaluated for VZV and measles serostatus, respectively. The seroprevalences of VZV and measles were 91% (1884/2070) and 70% (1284/1827), respectively. Younger HCWs had a significantly lower seroprevalence of measles (p = 0.02, age) and VZV (p = 0.003, birth year and p < 0.001, age). The seroprevalence of measles and VZV was significantly higher among doctors and nursing assistants than among nurses and other HCWs (p < 0.001 in both). In conclusion, the seroprevalence of measles and VZV significantly decreased in younger HCWs. Additionally, monitoring the serostatus of measles and VZV and the immunization of susceptible HCWs are required to prepare and control infectious diseases in healthcare facilities.

Long-term vaccine efficacy of a 2-dose varicella vaccine in China from 2011 to 2021: A retrospective observational study

Objective

A 2-dose varicella vaccine immunization strategy has been implemented in many cities in China, but there is few evidence on a long-term evaluation of the efficacy of the 2-dose varicella vaccine from China. This study aims to assess the long-term vaccine efficacy of the two doses varicella vaccine and analysis of its influencing factors.

Methods

A retrospective study was carried out in 837,144 children born between 2011 and 2017 in Ningbo, Easten China. The logistic regression was performed to estimate varicella vaccine effectiveness (VE).

Results

The overall VE of 2 doses of varicella vaccine compared without the vaccine was 90.31% (89.24-91.26%), and the overall incremental VE of 2 doses of varicella vaccine compared to the 1-dose was 64.71% (59.92-68.93%). Moreover, the varicella vaccination age of the second dose and the interval between 2 doses were both associated with VE. The VE compared to that without the vaccine in children vaccinated at <4 years old was 91.22% (95%CI: 90.16-92.17%) which was higher than in children vaccinated at ≥4 years old (VE: 86.79%; 95%CI: 84.52-88.73). And the effectiveness of the vaccine was 93.60% (95%CI: 92.19-94.75%) in children with the interval of the 2 doses ≤ 24 months significantly higher than in children with the interval of ≥36 months (VE: 85.62%, 95%CI: 82.89-87.91%).

Conclusions

This study provides evidence for long-term VE of the 2-dose varicella vaccine and the better age for 2-dose vaccination and the interval between 2 doses of the vaccine in China.

Early-Life Antibiotic Exposure Associated With Varicella Occurrence and Breakthrough Infections: Evidence From Nationwide Pre-Vaccination and Post-Vaccination Cohorts

Background

Antibiotic-driven dysbiosis may impair immune function and reduce vaccine-induced antibody titers.

Objectives

This study aims to investigate the impacts of early-life antibiotic exposure on subsequent varicella and breakthrough infections.

Methods

This is a nationwide matched cohort study. From Taiwan’s National Health Insurance Research Database, we initially enrolled 187,921 children born from 1997 to 2010. Since 2003, the Taiwan government has implemented a one-dose universal varicella vaccination program for children aged 1 year. We identified 82,716 children born during the period 1997 to 2003 (pre-vaccination era) and 48,254 children born from July 1, 2004, to 2009 (vaccination era). In the pre-vaccination era, 4,246 children exposed to antibiotics for at least 7 days within the first 2 years of life (Unvaccinated A-cohort) were compared with reference children not exposed to antibiotics (Unvaccinated R-cohort), with 1:1 matching for gender, propensity score, and non-antibiotic microbiota-altering medications. Using the same process, 9,531 children in the Vaccinated A-cohort and Vaccinated R-cohort were enrolled from the vaccination era and compared. The primary outcome was varicella. In each era, demographic characteristics were compared, and cumulative incidences of varicella were calculated. Cox proportional hazards model was used to examine associations.

Results

In the pre-vaccination era, the 5-year cumulative incidence of varicella in the Unvaccinated A-cohort (23.45%, 95% CI 22.20% to 24.70%) was significantly higher than in the Unvaccinated R-cohort (16.72%, 95% CI 15.62% to 17.82%) (p<.001). In the vaccination era, a significantly higher 5-year cumulative incidence of varicella was observed in the Vaccinated A-cohort (1.63%, 95% 1.32% to 1.93%) than in the Vaccinated R-cohort (1.19%, 95% CI 0.90% to 0.45%) (p=0.006). On multivariate analyses, early-life antibiotic exposure was an independent risk factor for varicella occurrence in the pre-vaccination (adjusted hazard ratio [aHR] 1.92, 95% CI 1.74 to 2.12) and vaccination eras (aHR 1.66, 95% CI 1.24 to 2.23). The use of penicillins, cephalosporins, macrolides, or sulfonamides in infancy was all positively associated with childhood varicella regardless of vaccine administration.

Conclusions

Antibiotic exposure in early life is associated with varicella occurrence and breakthrough infections.

Waning Effectiveness of One-dose Universal Varicella Vaccination in Korea, 2011-2018: a Propensity Score Matched National Population Cohort

BACKGROUND

Despite high coverage (~98%) of universal varicella vaccination (UVV) in the Republic of Korea since 2005, reduction in the incidence rate of varicella is not obvious. The study aimed to evaluate the vaccine effectiveness (VE) of one-dose UVV by timeline and severity of the disease.

METHODS

All children born in Korea in 2011 were included for this retrospective cohort study that analyzed insurance claims data from 2011-2018 and the varicella vaccination records in the immunization registry. Adjusted hazard ratios by Cox proportional hazard models were used to estimate the VE through propensity score matching by the month of birth, sex, healthcare utilization rate, and region.

RESULTS

Of the total 421,070 newborns in the 2011 birth cohort, 13,360 were matched for age, sex, healthcare utilization rate, and region by the propensity score matching method. A total of 55,940 (13.29%) children were diagnosed with varicella, with the incidence rate 24.2 per 1000 person-year; 13.4% of vaccinated children and 10.4% of unvaccinated children. The VE of one-dose UVV against any varicella was 86.1% (95% confidence interval [CI], 81.4-89.5) during the first year after vaccination and 49.9% (95% CI, 43.3-55.7) during the 6-year follow-up period since vaccination, resulting in a 7.2% annual decrease of VE. The overall VE for severe varicella was 66.3%. The VE of two-dose compared to one-dose was 73.4% (95% CI, 72.2-74.6).

CONCLUSION

We found lower long-term VE in one-dose vaccination and waning of effectiveness over time. Longer follow ups of the vaccinated children as well as appropriately designed studies are needed to establish the optimal strategy in preventing varicella in Korea.

Suitability of databases in the Asia-Pacific for collaborative monitoring of vaccine safety

INTRODUCTION

Information regarding availability of electronic healthcare databases in the Asia-Pacific region is critical for planning vaccine safety assessments particularly, as COVID-19 vaccines are introduced. This study aimed to identify data sources in the region, potentially suitable for vaccine safety surveillance. This manuscript is endorsed by the International Society for Pharmacoepidemiology (ISPE).

METHODS

Nineteen countries targeted for database reporting were identified using published country lists and review articles. Surveillance capacity was assessed using two surveys: a 9-item introductory survey and a 51-item full survey. Survey questions related to database characteristics, covariate and health outcome variables, vaccine exposure characteristics, access and governance, and dataset linkage capability. Other questions collated research/regulatory applications of the data and local publications detailing database use for research.

RESULTS

Eleven databases containing vaccine-specific information were identified across 8 countries. Databases were largely national in coverage (8/11, 73%), encompassed all ages (9/11, 82%) with population size from 1.4 to 52 million persons. Vaccine exposure information varied particularly for standardized vaccine codes (5/11, 46%), brand (7/11, 64%) and manufacturer (5/11, 46%). Outcome data were integrated with vaccine data in 6 (55%) databases and available via linkage in 5 (46%) databases. Data approval processes varied, impacting on timeliness of data access.

CONCLUSIONS

Variation in vaccine data availability, complexities in data access including, governance and data release approval procedures, together with requirement for data linkage for outcome information, all contribute to the challenges in building a distributed network for vaccine safety assessment in the Asia-Pacific and globally. Common data models (CDMs) may help expedite vaccine safety research across the region.

Epidemiology of varicella and effectiveness of varicella vaccine in Hangzhou, China, 2019

Background: The varicella vaccine (VarV) is not included in the national childhood immunization schedules in China, although 2-dose VarV (VarV2) were recommended for children at 1 and 4 years of age in Hangzhou since 2014. However, the reported incremental vaccine effectiveness (VE) of VarV2 varies widely among studies. We described the epidemiological characteristics of varicella in Hangzhou, assessed the VE of VarV, so as to provide scientific evidence on optimization and adjustment of immunization strategies for varicella prevention in China. Methods: All varicella cases diagnosed in a hospital in Hangzhou are reported to China Information System for Disease Control and Prevention (CISDCP). The demographic information of reported varicella cases onset from January 1 to December 31, 2019 was extracted from CISDCP on Jan 31, 2020. The demographic information was obtained from the information system of the National Center for Disease Prevention and Control. We conducted a 1:1 matched case-control study to assess the effectiveness of VarV. Participant data were collected with standardized questionnaires. VarV vaccination status was checked by using Hangzhou Immunization Information System (HZIIS). Results: A total of 11,813 varicella cases were reported in Hangzhou, China, 2019, without any death. Annual estimated incidence of varicella was 120 cases per 100,000 populations in 2019. The overall estimated incidence rate of varicella was high, especially for persons aged 10-19 years old and in suburb areas. The seasonal pattern was apparent, mostly due to the cases among students and children in kindergarten. In total, 218 varicella cases and 218 matched controls were included for evaluating the VE of VarV. VarV vaccination produced a high level of protection against varicella, while VE of VarV2 was even better. VE of VarV1 was 91.0% (95%CI: 81.6%-95.8%), and VE was 98.0% (95.5%-99.2%) for VarV2. Conclusion: Continuous monitoring and management of varicella cases is necessary, especially in those endemic areas, high-risk populations, and peak periods; a 2-dose VarV strategy is highly recommended, and relevant health institutions should consider the inclusion of VarV in the national immunization program to better control varicella epidemic and reduce the burden of varicella.

Global impact of varicella vaccination programs

Although varicella is usually a mild and self-limited disease, complications can occur. In 1998, the World Health Organization recommended varicella vaccination for countries where the disease has a significant public health burden. Nonetheless, concerns about a shift in the disease to older groups, an increase in herpes zoster in the elderly and cost-effectiveness led many countries to postpone universal varicella vaccine introduction. In this review, we summarize the accumulating evidence, available mostly from high and middle-income countries supporting a high impact of universal vaccination in reductions of the incidence of the disease and hospitalizations and its cost-effectiveness. We have also observed the effect of herd immunity and noted that there is no definitive and consistent association between vaccination and the increase in herpes zoster incidence in the elderly.

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

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

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.

Economic burden of varicella in children 1-12 years of age in Argentina, 2009-2014

BACKGROUND

In Argentina, varicella vaccination was included in the national schedule for mandatory immunizations in 2015. The vaccine has been shown to substantially reduce the morbidity and mortality associated with the virus. The purpose of this study was to evaluate the clinical and economic burden associated with varicella in Argentina prior to vaccine introduction.

METHODS

This was a multi-center, retrospective chart review study among patients aged 1-12 years with a primary varicella diagnosis in 2009-2014 in Argentina. Healthcare resource utilization (HCRU) associated with varicella and its complications, unit costs, and work loss were used to estimate direct and indirect costs. All costs are presented in 2015 United States dollars (USD).

RESULTS

One hundred and fifty children with varicella were included (75 outpatients, 75 inpatients), with a mean age of 3.8 (SD = 2.4) and 2.9 (SD = 2.2) years, respectively. One or more complications were experienced by 28.0% of outpatients and 98.7% of inpatients, the most common being skin and soft tissue infections, pneumonia, sepsis, cerebellitis, and febrile seizure. HCRU estimates included use of over-the-counter (OTC) medications (58.7% outpatients, 94.7% inpatients), prescription medications (26.7% outpatients, 77.3% inpatients), tests/procedures (13.3% outpatients, 70.7% inpatients), and consultation with allied health professionals (1.3% outpatients, 32.0% inpatients). The average duration of hospital stay was 4.9 (95% CI = 4.2-5.7) days, and the average duration of ICU stay was 4.8 (95% CI = 1.6-14.1) days. The total combined direct and indirect cost per varicella case was 2947.7 USD (inpatients) and 322.7 USD (outpatients). The overall annual cost of varicella in Argentina for children aged ≤14 years in 2015 was estimated at 40,054,378.0 USD.

CONCLUSION

The clinical burden of varicella in Argentina was associated with utilization of significant amounts of healthcare resources, resulting in substantial economic costs. These costs should be reduced with the recent implementation of routine vaccination of children.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Assessing varicella vaccine effectiveness and its influencing factors using health insurance claims data, Germany, 2006 to 2015

In Germany, routine childhood varicella vaccination was implemented in 2004 with two doses recommended since 2009. We used an immunisation information system based on countrywide health insurance claims data to analyse vaccine effectiveness (VE) and factors influencing VE. We applied proportional hazard models to estimate VE under various conditions and compared the risk of acquiring varicella among unvaccinated children in regions with high vs low vaccination coverage (VC). Among 1.4 million children we identified 29,404 varicella cases over a maximum follow-up of 8 years post-vaccination. One-dose VE was 81.9% (95% confidence interval (CI): 81.4–82.5), two-dose VE 94.4% (95% CI: 94.2–94.6). With dose one given 1–27 days after measles-containing vaccine (MCV), one-dose VE was 32.2% (95% CI: 10.4–48.6), two-dose VE 92.8% (95% CI: 84.8–96.6). VE was not associated with age at vaccination (11–14 vs ≥ 15 months), time since vaccination, or vaccine type. Unvaccinated children had a twofold higher risk of acquiring varicella in low VC regions. Our system generated valuable data, showing that two-dose varicella vaccination provides good protection for at least 8 years. Unvaccinated children benefit from herd effects. When the first varicella vaccine dose is given shortly after MCV, a second dose is essential.

Epidemiological characteristics of breakthrough varicella infection during varicella outbreaks in Shanghai, 2008-2014

The outbreaks of varicella occurring in kindergartens and schools are increasingly notified in Shanghai despite the implementation of one-dose varicella vaccination. We analyzed surveillance data on the notified outbreaks of varicella in Minhang District of Shanghai during 2008-2014. A total of 13 511 varicella cases and 154 outbreaks involving 1558 (11·5%) cases were reported. Annual attack rates of outbreak-associated varicella in outbreak classes were 5·5%-12%. The mean age of the outbreak-associated cases was 8·6 ± 3·1 years. Among 1558 outbreak cases, 660 (42·4%) received one-dose varicella vaccine previously. The proportions of breakthrough varicella infection during outbreaks ranged from 21·5% in 2008 to 86·1% in 2014. Annual breakthrough infection rates in outbreak classes ranged from 5·4% to 7·4%. Breakthrough cases as index cases results in 9·7% of outbreaks, and the average duration of outbreaks was significantly longer in vaccinated cases as index cases than in unvaccinated cases as index cases (11·3 ± 5·8 days vs. 8·6 ± 6·1 days, P < 0·05). The mean time of breakthrough infection since vaccination was 6·2 ± 2·3 years (range 0·6-13·4 years). One-dose varicella vaccination cannot prevent the varicella outbreaks in kindergartens and schools. A second dose of varicella vaccine should be recommended for children.

Voluntarily Reported Immunization Registry Data: Reliability and Feasibility to Predict Immunization Rates, San Diego, California, 2013

OBJECTIVES

Accurate data on immunization coverage levels are essential to public health program planning. Reliability of coverage estimates derived from immunization information systems (IISs) in states where immunization reporting by medical providers is not mandated by the state may be compromised by low rates of participation. To overcome this problem, data on coverage rates are often acquired through random-digit-dial telephone surveys, which require substantial time and resources. This project tested both the reliability of voluntarily reported IIS data and the feasibility of using these data to estimate regional immunization rates.

METHODS

We matched telephone survey records for 553 patients aged 19-35 months obtained in 2013 to 430 records in the San Diego County IIS. We assessed concordance between survey data and IIS data using κ to measure the degree of nonrandom agreement. We used multivariable logistic regression models to investigate differences among demographic variables between the 2 data sets. These models were used to construct weights that enabled us to predict immunization rates in areas where reporting is not mandated.

RESULTS

We found moderate agreement between the telephone survey and the IIS for the diphtheria, tetanus, and acellular pertussis (κ = 0.49), pneumococcal conjugate (κ = 0.49), and Haemophilus influenzae type b (κ = 0.46) vaccines; fair agreement for the varicella (κ = 0.39), polio (κ = 0.39), and measles, mumps, and rubella (κ = 0.35) vaccines; and slight agreement for the hepatitis B vaccine (κ = 0.17).

CONCLUSIONS

Consistency in factors predicting immunization coverage levels in a telephone survey and IIS data confirmed the feasibility of using voluntarily reported IIS data to assess immunization rates in children aged 19-35 months.

Severe varicella in persons vaccinated with varicella vaccine (breakthrough varicella): a systematic literature review

INTRODUCTION

Varicella vaccines are highly effective at preventing disease, but varicella may occur among vaccinated persons (termed breakthrough varicella). Breakthrough varicella is generally mild, but severe cases have been reported. The objective of this review is to describe severe breakthrough varicella. Areas covered: We conducted a systematic review of articles published during 1974-2016. A total of 34 articles were included in our review: 21 described breakthrough varicella with disseminated varicella-zoster virus (VZV) infection with other organ involvement in addition to skin (none among two-dose vaccinees); 9 described hospitalized breakthrough varicella without mention of other organ involvement in addition to skin (of which 2 reported 4 two-dose vaccinees); and 4 described both. A total of 52-60 unique breakthrough varicella cases with disseminated VZV infection with other organ involvement in addition to skin reported with the following complications, not mutually exclusive: pneumonia (n = 8-9 cases), neurologic (n = 18-24 cases), hematologic (n = 10-11 cases), ocular (n = 5 cases), renal (n = 2 cases), hepatic (n = 3 cases), secondary infection with bacteremia or sepsis (n = 8 cases), and other complication (n = 4 cases). There were 6 cases of fatal breakthrough varicella. Expert commentary: With >31 million doses distributed annually worldwide since 2007, severe breakthrough varicella can occur but they appear to be uncommon.

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.

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.

Seroepidemiology of varicella-zoster virus in Korean adolescents and adults using fluorescent antibody to membrane antigen test

We conducted a cross-sectional seroepidemiological study in 2012–2013 to determine the seroprevalence of varicella-zoster virus (VZV) in adolescents and adults living in Korea, where varicella vaccination has been recommended universally at age 12–15 months since 2005. Residual serum samples were collected from 1196 healthy adults and adolescents aged ⩾10 years between November 2012 and March 2013. The fluorescent antibody to membrane antigen (FAMA) test and enzyme-linked immunosorbent assay (ELISA) were performed to determine the seroprevalence of VZV. The seroprevalences of VZV were compared between six age groups: 10–19, 20–29, 30–39, 40–49, 50–59, and ⩾60 years. The seroprevalence of VZV in the entire study cohort was 99·1% according to the FAMA test and 93·1% as determined by ELISA. The seroprevalences of the six age groups were as follows: 96·0%, 99·5%, 99·5%, 99·5%, 100%, and 100%, respectively, by the FAMA test, and 83·3%, 93·0%, 93·0%, 97·5%, 94·5%, and 97·5%, respectively, by ELISA. Seroprevalence increased significantly with age (P < 0·001); moreover, the seroprevalence in subjects aged 10–19 years was significantly lower than in other age groups (P < 0·001), as measured by both the FAMA test and ELISA. Thus, strategies to increase protective immunity against VZV in teenagers are necessary.

Varicella and varicella vaccination in South Korea

With continuing occurrence of varicella despite increasing vaccine coverage for the past 20 years, a case-based study, a case-control study, and an immunogenicity and safety study were conducted to address the impact of varicella vaccination in South Korea. Varicella patients under the age of 16 years were enrolled for the case-based study. For the case-control study, varicella patients between 12 months and 15 years of age were enrolled with one control matched for each patient. For the immunogenicity and safety study, otherwise healthy children from 12 to 24 months old were immunized with Suduvax (Green Cross, South Korea). Fluorescent antibody to membrane antigen (FAMA) varicella-zoster virus (VZV) antibody was measured before and 6 weeks after immunization. In the case-based study, the median age of the patients was 4 years. Among 152 patients between 1 and 15 years of age, 139 children received varicella vaccine and all had breakthrough infections. Clinical courses were not ameliorated in vaccinated patients, but more vaccinated patients received outpatient rather than inpatient care. In the case-control study, the adjusted overall effectiveness of varicella vaccination was 54%. In the immunogenicity and safety study, the seroconversion rate and geometric mean titer for FAMA antibody were 76.67% and 5.31. Even with increasing varicella vaccine uptake, we illustrate no upward age shift in the peak incidence, a high proportion of breakthrough disease, almost no amelioration in disease presentation by vaccination, and insufficient immunogenicity of domestic varicella vaccine. There is need to improve the varicella vaccine used in South Korea.

Determinants of varicella breakthrough: results of a 2012 case control study

This study aims to evaluate the determinants of breakthrough infection after one dose of varicella vaccine. We designed a retrospective case-control study. Breakthrough cases were children, aged 1-15, who presented varicella symptoms ≥ 42 days after the first dose of varicella vaccine (breakthrough). Controls were children, aged 1-15 years, who attended the same class (in a school or in a kindergarten) than the cases in the year of the breakthrough onset; they received a dose of varicella vaccine ≥ 42 days before the case rash onset and they did not develop varicella symptoms. We enrolled 45 cases and 135 controls. 40% of cases (n = 18; 95% CI = 25.4-54.6) presented at least one risk factor; this proportion was 39.2% (95% CI = 30.9-47.6) among the controls (chi-square = 0.0078; P = 0.93). Time between vaccination and virus exposure was longer among cases. Logistic regression showed that breakthrough disease was associated with duration of time from vaccination.

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.

Immunogenicity and safety of combined measles-mumps-rubella-varicella vaccine using new measles and rubella working seeds in healthy children in Taiwan and Singapore: a phase II, randomized, double-blind trial

AIM

This study evaluated the immunogenicity and safety of tetravalent measles-mumps-rubella-varicella (MMRV) vaccine produced with measles and rubella monovalent bulks derived from a newly established working seed virus stock (MMRV(new WS)) compared with the combined MMRV vaccine derived from the current seed virus stock, in Taiwanese and Singaporean children (NCT00892775).

METHODS

Healthy children aged 11-22 mo were randomized to receive two doses of either the MMRV(new WS) vaccine or the MMRV vaccine. Antibody titers against measles, mumps and rubella were measured using ELISA and against varicella using an immunofluorescence assay. The primary objective was to demonstrate non-inferiority of MMRV(new WS) to MMRV in terms of post-dose-1 seroconversion rates, defined as a group difference with a lower limit of the 95% confidence interval greater than -10% for each antigen. Parents/guardians recorded symptoms in diary cards for 43 d after each vaccine dose.

RESULTS

Non-inferiority of MMRV(new WS) to MMRV was achieved for all vaccine antigens. The lower limits of the 95% confidence intervals for group differences (MMRV(new WS) group vs. MMRV) for measles (99.4% vs 100%), mumps (89.7% vs 90.4%), rubella (99.7% vs 100%) and varicella (97.6% vs 92.9%) seroconversion rates were greater than -10%. Mild symptoms including a peak in fever between days 5 and 12, post-dose-1, was observed in both groups.

CONCLUSION

The immune responses elicited by the MMRV(new WS) vaccine were non-inferior to that elicited by the MMRV vaccine for all antigens. Both vaccines exhibited an acceptable safety profile in Taiwanese and Singaporean children.

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.

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.

Molecular studies of the Oka varicella vaccine

Varicella zoster virus (VZV) is one of eight members of the Herpesviridae family for which humans are the primary host; it causes two distinct diseases, varicella (chickenpox) and zoster (shingles). Varicella results from primary infection, during which the virus establishes latency in sensory neurons, a characteristic of all members of the Alphaherpesvirinae subfamily. Zoster is caused by reactivation of latent virus, which typically occurs when cellular immunity is impaired. VZV is the first human herpesvirus for which a vaccine has been licensed. The vaccine preparation, v-Oka, is a live-attenuated virus stock produced by the classic method of tissue culture passage in animal and human cell lines. Over 90 million doses of the vaccine have been administered in countries worldwide, including the USA, where varicella morbidity and mortality has declined dramatically. Over the last decade, several laboratories have been committed to investigating the mechanism by which the Oka vaccine is attenuated. Mutations have accumulated across the genome of the vaccine during the attenuation process; however, studies of the contribution of these changes to vaccine attenuation have been hampered by the lack of a suitable animal model of VZV disease and by the heterogeneity that exists among the viral population within the vaccine preparation. Notwithstanding, a wealth of data has been generated using various laboratory methodologies. Studies of the vaccine virus in human xenografts implanted in severe combined immunodeficiency-hu mice, have enabled analyses of the replication dynamics of the vaccine in dorsal root ganglia, T lymphocytes and skin. In vitro assays have been used to investigate the effect of vaccine mutations on viral gene expression and sequence analysis of vaccine rash viruses has permitted investigations into spread of the vaccine virus in a human host. We present here a review of what has been learned thus far about the molecular and phenotypic characteristics of the Oka vaccine.