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

Spatiotemporal distribution of varicella in the Republic of Korea

Varicella is a highly contagious disease caused by the varicella-zoster virus (VZV). Given its tendency to cluster geographically, spatial analyses may provide a better understanding of the pattern of varicella transmission. We investigated the spatial characteristics of varicella in Korea and the risk factors for varicella at a national level. Using national surveillance and demographic data, we examined the spatial distribution of incidence rates and their spatial autocorrelation and calculated Moran's index. Spatial regression analysis was used to identify sociodemographic predictors of varicella incidence at the district level. An increasing tendency in the annual incidence of varicella was observed over a 12-year period (2006-2018), with a surge in 2017. There was a clear positive spatial autocorrelation of the varicella incidence rate during the surveillance period. During 2006-2014, High-High (HH) clusters were mostly confined to the northeast region and neighboring districts. The spatial error model showed that population density had a negative coefficient and childhood percentage, percentage of children under 12 years of age among the total population, had positive coefficient, whereas vaccine coverage was insignificant. The varicella incidence according to geographic region varied with population density, childhood percentage, suggesting the importance of community-level surveillance and monitoring strategies.

Effectiveness of one-dose versus two-dose varicella vaccine in children in Qingdao, China: a matched case-control study

To evaluate whether two-dose of varicella vaccine would provide a better protection to children from varicella than one-dose, we conducted a 1:3 matched case-control study in children in Qingdao, China. A total of 509 varicella cases aged 6-11 y were collected from the China Information System for Disease Control and Prevention (CISDCP). And 1,527 controls, who did not suffer from varicella, were selected and matched with cases by age and class. The varicella vaccine effectiveness (VE) and corresponding 95% confidence interval (95% CI) were calculated. The vaccination coverage rate of one-dose varicella vaccine in the cases was 52.9%, while for the controls was 59.1%. And the two-dose vaccination rate in the cases and controls were 4.3% and 14.5%, respectively. A statistically significant difference was found in the immunization history between the cases and controls (P < .001).The overall varicella VE was 56.1% (95% CI: 45.0%-64.9%), and the VE of two-dose vaccination (81.6%, 95% CI: 70.5%-88.4%) was substantially higher than that of one-dose vaccination (44.7%, 95% CI: 31.6%-55.4%). For less than 2 y, 2-4 y, 4-6 y, and more than 6 y after only one-dose vaccination, the varicella VE were 96.6% (95% CI: 75.0%-99.5%), 81.2% (95% CI: 55.6%-92.0%), 60.8% (95% CI: 46.8%-70.2%), and 18.0% (95% CI: 4.3%-35.6%), respectively. The varicella VE gradually decreased over time (P for trend < 0.001). It is recommended that the coverage of varicella vaccine should be increased and two-dose of varicella vaccine should be included in the National Immunization Program of China.

Uptrend prevalence of varicella parallel with low serum antibodies and low second-dose rate among children 10-14 years old in Wenzhou, China

In recent years, the incidence of varicella cases is rising, and outbreaks of varicella are frequently being reported worldwide. Our study aims to analyze the association between the varicella incidence and serum antibody level in the post-vaccine era. We retrieved and analyzed the incidence and prevalence data for children age 1-14 years in Wenzhou, China during 2010-2018. A cross-sectional seroepidemiology analysis was carried out in a series of 168 general healthy children age 1-14 years as well as children at a varicella outbreak in Wenzhou. Our data showed a significant surge in the incidence and prevalence of varicella in children aged 10-14 years in 2017 and 2018 while they were kept relatively stable in 2010-2016. The seroepidemiological analysis revealed a 7.3-fold significantly higher level of serum varicella IgG in healthy control students who exposed at the outbreak than that in general healthy children (median 523.5 vs. 71.7 mIU/mL, p < .01). The children 10-14 years old had the lowest rate of second-dose vaccination among the three age classes (7%, 41%, and 65% in 10-14, 5-9, and 2-4 age class, respectively), and children 5-9 years old who received the second dose had a higher level of serum protective IgG than those who did not (254.7 vs 98 mIU/mL, p = .06). The findings from the present study warn a two-dose vaccine schedule to reduce the climbing incidence and prevalence observed in the older children and suggest a higher serum IgG threshold for effective protection of children from the varicella outbreak.

Evaluation of impact of one dose varicella vaccine on the incidence of chickenpox in Argentina

INTRODUCTION

Varicella, also known as chickenpox is one of the most common immunizable diseases. In 1998, the World Health Organization (WHO) recommended to incorporate this vaccine in the national immunization programs, which Argentina did in 2015.

OBJECTIVES

To describe the behavior of the varicella time series for the 2005-2017 period, and to evaluate the impact of the vaccine in Argentina.

METHODOLOGY

An ecological observational study was performed, using the varicella cases reported in the National Health Monitoring System, and the data of the National census as secondary data sources. A model based time series analysis of the notified varicella cases in Argentina was performed, using a Negative Binomial Mixed Model. For the verification of the vaccine impact, the 2005-2014 period was selected, and a prognosis for the following years was performed. Impact was evaluated by comparing the rates and confidence intervals between the predicted and observed values.

RESULTS

Argentina reported 1,775,587 varicella cases for the 2005-2017 period. The series exhibited seasonality, and, a decreasing trend in the number of cases was observed in 2016 and 2017. A reduction of the incidence rate after the implementation of the vaccine was observed. The transmission risk decreased in the country after vaccine implementation.

CONCLUSIONS

This study is the first concrete evidence of the varicella incidence decline after the implementation of a single dose application program in Argentina.

Burden of varicella in the Asia-Pacific region: a systematic literature review

INTRODUCTION

Varicella is a highly contagious infection that can lead to serious complications, particularly in high-risk groups; however, it is vaccine preventable. Disease awareness and understanding of the disease burden can strongly influence vaccine coverage. This review provides insight into the current epidemiology and the importance of varicella from both public health and economic perspectives across the Asia-Pacific (APAC) region. Areas covered: A systematic literature review was conducted to identify studies on the incidence, seroprevalence, fatality rate and complication rate of varicella. Economic burden studies were also captured. Altogether, 125 studies were identified across the region; these were supplemented by government reports (gray data). Reported vaccine coverage varied from 2.8% to 97%; a key influencing factor was inclusion of the varicella vaccine in national immunization programs. In general, varicella incidence in the unvaccinated population was highest in children ≤5 years old and seroprevalence increased with age. Economic analyses highlighted the cost-saving potential of vaccination programs, especially from a societal perspective. Expert opinion: Varicella-related data varied greatly across the APAC region, highlighting the need to better understand the burden of varicella in this area, and particularly identified the need for better surveillance and reporting.

Increasing varicella incidence rates among children in the Republic of Korea: an age-period-cohort analysis

In the Republic of Korea, despite the introduction of one-dose universal varicella vaccination in 2005 and achieving a high coverage rate of 98.9% in 2012, the incidence rate has been increased sevenfold. This study aimed to investigate time trends of varicella incidence rate, assessing the age, period and birth cohort effects. We used national data on the annual number of reported cases from 2006 to 2017. A log-linear Poisson regression model was used to estimate age-period-cohort effects on varicella incidence rate. From 2006 to 2017, the incidence of varicella increased from 22.5 cases to more than 154.8 cases per 100 000. Peak incidence has shifted from 4 to 6 years old. The estimated period and cohort effects showed significant upward patterns, with a linear increasing trend by net drift. There has been an increase in the incidence among the Korean population regarding period and cohort despite the universal vaccination of varicella vaccine. Our data suggest the need for additional studies to address the current gap in herd immunity.

[Decrease in the incidence of chickenpox in the Community of Madrid after universal childhood immunization. Years 2001-2015]

OBJECTIVE

Varicella vaccine was recommended in the Community of Madrid (CM) at 15months of age between November 2006 and December 2013. The objective was to describe the impact of vaccination on the incidence of varicella in the CM during the period 2001-2015.

DESIGN

A descriptive study of cases of varicella reported to the Sentinel Physician Network of the CM and the cases recorded in the Minimum Basic Data Set at hospital discharge was carried out. Total incidence of cases and of hospital admissions were calculated, as well as specific incidence by age and sex.

RESULTS

The incidence was 94.0% lower between 2012 and 2013 than between 2001 and 2003. Between 2014 and 2015 the incidence was 61.8% higher than between 2012 and 2013. The highest incidence was observed in children aged 0 to 4years except for 2010-2014, which was exceeded by the incidence in children aged 5 to 9. The trend in hospital admissions was also decreasing, with the highest incidence in children aged 0 to 1year, followed by 1-4years.

CONCLUSIONS

There has been a significant decrease in the incidence of cases and of hospital admissions by varicella in all age groups after the recommendation to vaccinate at 15months of age, which is compatible with the effectiveness of a dose and its ability to produce immunity group. The withdrawal of this recommendation between 2014 and 2015 has led to an increase in the incidence.

One-dose vaccination associated with attenuated disease severity of adolescent and adult varicella cases in Beijing's Fengtai District

BACKGROUND

In recent years, the number of varicella cases in adults has significantly increased in Beijing. However, the effect of the vaccination on varicella-related characteristics among adults has not been studied.

METHODS AND RESULTS

Using data from the Infectious Disease Reporting System and the Immunization Information System, we compared the epidemiology and disease severity in breakthrough and unvaccinated varicella cases in adolescents and adults (≥ 15 year-old) from 2008 to 2011 in Beijing's Fengtai district, China. The results showed that the age (P = 0.003),contact history (90% vs. 73%, P = 0.019) and outbreak cases (10% vs. 1%, P < 0.0001) were significantly differently distributed between the two groups and that both the incidence of moderate-to-severe cases (26% vs. 45%, P = 0.035, OR = 0.446) and varicella-associated fever (49% vs. 66%, P = 0.068, OR = 0.534) were either significantly lower or trended to be lower in the breakthrough group than in the unvaccinated group. Additionally,vaccine effectiveness against moderate-to-severe cases of varicella was 55.4%.

CONCLUSION

Altogether, these results indicate that vaccination against varicella among adolescents and adults affected the epidemiology and attenuated the disease severity of the cases. The Results from this study will provide useful information for the prevention of varicella in adolescents and adults.

Varicella vaccine uptake and associated factors in children in Hong Kong

Varicella is a common and highly contagious childhood disease which impacts the public worldwide. Hong Kong children can only be vaccinated against the disease in private practice. The varicella vaccination rate of local children in preschool is uncertain. Therefore a cross-sectional kindergarten-based parent-administered questionnaire survey was conducted in Hong Kong during 2012. Twelve kindergartens were randomly selected from a complete school list from the Education Bureau of Hong Kong. In total, 1285/1538 (83·6%) parents consented to join the study and completed the questionnaires. The overall varicella infection rate was 19·5% and the uptake of varicella vaccination rate was 57·6%. Barriers against varicella vaccination were mostly due to parental uncertainties about the effectiveness of vaccine, lack of recommendations from doctors or government, and adverse side-effects of the vaccine. The government and healthcare professional bodies are strongly recommended to further enhance health education among healthcare professionals, encouraging their active promotion of varicella vaccination for their patients. Furthermore, health education through various stakeholders is crucial to enhance parental awareness of varicella, as well as the effectiveness and safety of varicella vaccine.

Analyzing titers of antibodies against bacterial and viral antigens, and bacterial toxoids in the intravenous immunoglobulins utilized in Taiwan

Intravenous immunoglobulin (IVIG) manufactured from human plasma contains IgG as the primary ingredient, and is used for indications such as immunodeficiency syndrome. Available IVIGs in Taiwan are either manufactured from Taiwanese or North American plasma. The effectiveness of the national immunization program of Taiwan can be evaluated by analyzing and comparing IVIG antibody titers that are induced through the corresponding vaccines (tetanus, diphtheria, and pertussis, measles, rubella, hepatitis A, hepatitis B and varicella). Both enzyme-linked immunosorbent assay (ELISA) and the in vitro neutralization test demonstrated that all IVIGs provide adequate clinical protection against diphtheria and tetanus toxins. ELISA results further revealed that plasma of Taiwanese subjects contains higher levels of pertussis toxin and filamentous hemagglutinin antibodies, when compared to foreign IVIGs. This may be related to the later adoption of acellular pertussis vaccine in Taiwan. Antibodies titers against measles, rubella, hepatitis A, and varicella-zoster virus were otherwise low. Low titers of hepatitis B surface antigen antibodies are present in Taiwanese plasma IVIG, indicating immune memory decline or loss. In conclusion, our results show that Taiwanese IVIG contains varying titers of vaccine-induced antibodies, and serves as a guide for future amendments to Taiwan's immunization program.

Epidemiological characteristics of varicella from 2000 to 2008 and the impact of nationwide immunization in Taiwan

Background

Varicella has an important impact on public health. Starting in 2004 in Taiwan, nationwide free varicella vaccinations were given to 1-year-old children.

Methods

Our study investigated the epidemiological characteristics of varicella from 2000 to 2008, and assessed the change of varicella epidemiology after the mass varicella immunization. ICD-9-CM codes related to varicella or chickenpox (052, 052.1, 052.2, 052.7, 052.8, 052.9) were analyzed for all young people under 20 years of age through the National Health Insurance database of Taiwan from 2000 to 2008.

Results

Case numbers of varicella or chickenpox significantly declined after the nationwide immunization in 2004. Winter, particularly January, was the epidemic season of varicella. We found a significant post-vaccination decrease in incidence among preschool children, especially 3 to 6 year-old children-- the peak incidence was 66 per thousand for 4 and 5 year-old children before the nationwide immunization (2000 to 2003), and the peak incidence was 23 per thousand for 6 year-old children in 2008 (p < 0.001). Varicella-related hospitalization also significantly decreased in children younger than 6 years after the nationwide immunization.

Conclusion

The varicella annual incidence and varicella-related hospitalization markedly declined in preschool children after nationwide varicella immunization in 2004.

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.