The impact of the universal infant varicella immunization strategy on Canadian varicella-related hospitalization rates

Population immunity to varicella in Canada: A Canadian Immunization Research Network (CIRN) study

INTRODUCTION

The incidence of varicella in Canada has decreased by almost 99% since vaccination was introduced. However, variation in the timing and eligibility of vaccination programs across the country has resulted in some cohorts being under-vaccinated and therefore potentially susceptible to infection.

METHODS

We used nationally representative specimens from the Biobank of Statistics Canada's Canadian Health Measures Survey (CHMS) as well as residual specimens from Ontario collected between 2009-2014 to estimate population immunity across age-groups and geography, and identify any groups at increased risk of varicella infection.

RESULTS

The weighted proportion of specimens with antibody levels above the threshold of protection was 93.6% (95% CI: 92.4, 95.0). Protection was lowest among those aged 3-5 years (54.3%; 95% CI: 47.3, 61.4), but increased with age. Individuals born outside Canada had more than twice the odds of varicella susceptibility than those born in Canada (aOR: 2.7; 95% CI: 1.4, 5.0; p = 0.004). There were no differences by sex or geography within Canada, and there were no statistically significant differences when Ontario CHMS sera were compared to Ontario residual sera, apart from in participants aged 12-19 year age-group, for whom the CHMS estimate (91.2%; 95% CI: 86.7, 95.7) was significantly higher (p = 0.03) than that from residual specimens (85.9%, 95% CI: 81.1, 90.8).

DISCUSSION

Varicella immunity in Canada is changing. Children appear to have low population immunity, placing them at greater risk of infection and at increased risk of severe disease as they age. Our results underscore the importance of performing periodic serosurveys to monitor further population immunity changes as the proportion of vaccine-eligible birth-cohorts increases, and to continually assess the risk of outbreaks.

The impact of varicella vaccination: A 2005-2019 interrupted time series analysis

Varicella is an acute, highly contagious disease in susceptible individuals and is preventable through vaccination. This study aimed to determine the impact of varicella vaccination on hospitalizations and complications at a pediatric reference hospital in Panama before and after the vaccine introduction. This descriptive ecological study analyzed clinical records of patients diagnosed with varicella through a retrospective and interrupted time series analysis. An autoregressive integrated moving average model was built to compare the incidence rates observed after vaccination with those expected rates derived from the model. A statistical model was fitted to the observed interrupted time series data by regression and used to predict future trends. The mean difference in varicella hospital discharges before and after the introduction of the varicella vaccine was 47%. The rate of hospitalizations for varicella decreased to 52.3%. A declining trend in varicella hospitalizations was observed from 2015 after vaccine introduction in 2014. Complications in vaccinated patients were secondary skin and soft tissue infection, possibly due to bacterial superinfection. The impact of varicella vaccination on reducing varicella hospital discharges reported at a pediatric reference hospital in Panama was confirmed.

Trends in age-specific varicella incidences following the introduction of the general recommendation for varicella immunization in Germany, 2006-2022

BACKGROUND

In Germany, general childhood varicella vaccination has been recommended since 2004. A feared effect of low vaccination coverage is a possible shift in incidence from children to teenagers and young adults who are at higher risk of severe outcomes. If true, this shift would possibly necessitate changes to the national immunization strategy. We aimed to evaluate the effects of the general vaccination recommendation on age-specific varicella incidences in Germany in general and examine specifically whether a shift from children to teenagers (15 to 19 years) has occurred.

METHODS

Trends in age-specific incidences were evaluated using triangulation with the following datasets: national mandatory notification data (N) (2014-2022), billing data of the statutory health insurance associations (I) (2009-2017) and data from a doctor's sentinel system (S) (2006-2017). Similar clinical case definitions were used in N and S, while I used ICD-10-codes. Age groups were stratified as available in all three systems. Incidences per year were calculated based on the total population (N), the number of statutory health insured (I), and extrapolated from S to the total population.

RESULTS

During all years of observation, age-specific incidences have dropped significantly across all age-groups for S und I. The age groups (under 10 years) with initially highest incidences were the ones with the strongest reductions (under 1 year: -90%, 1-4 years: -95.5%, 5-9 years: -89.2% for S; -67.7%, -78%, -79.3% for I). A single 53.1% increase in the low incidence in S among 15-19-year olds observed in 2017 compared to 2016 could not be confirmed in N or I. Increases in incidences during the first two years of N are probably due to improved notification behaviour over these years. In 2019, all age-specific incidences increased (N), with 15 to 19-year olds showing the highest relative increase (28.2%).

CONCLUSIONS

Since the introduction of the general vaccine recommendation against varicella, incidences across all age-groups have declined significantly. Available data indicate no evidence for a shift in disease incidence to older age groups. Every incidence increase beyond childhood age should however be followed up closely. So far, children and adolescents have both benefitted from the current vaccination strategy.

Impact of implementing a free varicella vaccination policy on incidence in Wuxi City, China: an interrupted time series analysis

Varicella vaccination is optional and requires self-payment. On 1 December 2018, Wuxi City launched a free varicella vaccination program for children. This study aimed to evaluate the changes in varicella incidence before and after the implementation of the policy. The data were obtained from official information systems and statistical yearbooks. We divided the period into chargeable (January 2017 to November 2018) and free (December 2018 to December 2021) periods. Interrupt time series analysis was used to conduct a generalised least-squares regression analysis for the two periods. A total of 51,071 varicella cases were reported between January 2017 and December 2021. After the implementation of the policy, there was a statistically significant decrease in the incidence of varicella (β2 = -0.140, P = 0.017), and the slope of the incidence also decreased by 0.012 (P = 0.015). Following policy implementation, the incidence decreased in all age groups, with the largest decline observed among children aged 8-14 years (β2 = -1.109, P = 0.009), followed by children aged ≤7 years (β2 = -0.894, P = 0.013). Our study found a significant reduction in the incidence of varicella in the total population after the introduction of free varicella vaccination in Wuxi City.

Immunization status of children at kindergarten entry in Alberta, Canada

OBJECTIVES

Little is known about immunization coverage among kindergarten-aged children in jurisdictions that do not require children's immunization records to be provided at school entry. Thus, we assessed immunization coverage and associated characteristics of a 2008 birth cohort of Alberta children at kindergarten entry as compared with at the end of grade one.

METHODS

This retrospective cohort study used population-based administrative health data for childhood vaccines in Alberta, Canada. We categorized and compared immunization status of children as follows: (a) complete at kindergarten entry; (b) incomplete at kindergarten entry but complete at the end of grade one; and (c) still incomplete at the end of grade one. To assess factors associated with immunization status, we used multinomial logistic regression.

RESULTS

Immunization coverage for the complete vaccine series for children (N = 41,515) at kindergarten entry was suboptimal (44.5%, 95% CI 44.0-45.0) and substantially lower than for children at the end of grade one (74.8%, 95% CI 74.3-75.2). Young maternal age, not living with a partner, and having > 1 child in a household were associated with incomplete immunization status at kindergarten entry. Midwife-assisted hospital and home delivery was strongly associated with incomplete immunization status at the end of grade one.

CONCLUSION

Immunization coverage at kindergarten entry was strikingly low. Risk factors for incomplete immunization status were identified that require particular attention when addressing immunization coverage. The school-based catch-up immunization program in grade one seems to have substantially improved coverage among children, suggesting a potential benefit of shifting the catch-up program from grade one to kindergarten entry.

Has Clinical and Epidemiological Varicella Burden Changed over Time in Children? Overview on Hospitalizations, Comorbidities and Costs from 2010 to 2017 in Italy

According to WHO estimates, varicella disease is responsible of a worldwide significant burden in terms of hospitalizations, complications, and deaths, with more than 90% of cases under 12 years old. This study aims at evaluating the clinical, epidemiological, and economic burden of varicella in Ligurian children, about comorbidities, organizational variables, and vaccination coverages from 2010 to 2017, in terms of Emergency Department accesses and hospitalizations. The overall hospitalization rate was 179.76 (per 100,000 inhab.), with a gradual but significant decline since 2015, when universal varicella vaccination was introduced in Liguria (p < 0.0001). The risk of being hospitalized for complicated varicella in subjects with at least one comorbidity was significantly higher than in subjects without comorbidities (p = 0.0016). The economic analysis showed higher costs in subjects with complicated varicella who were 0-3 years old. This age group showed higher costs also considering extra-hospital costs for both outpatient procedures and pharmaceutical costs (p < 0.0001). The results confirm the relevant burden of varicella, especially in the 0-3 age group and in children with comorbidities. Thus, vaccination with the achievement of adequate vaccination coverages is confirmed to be a necessary control strategy to reduce hospitalizations and associated complications with important economic benefits.

Impact of six years of routine varicella vaccination on the disease-related hospitalizations at Minas Gerais, Brazil

INTRODUCTION

The varicella vaccine was first introduced into the Brazilian immunization schedule in September 2013 as a single dose for children aged 15 months. In 2018, a second dose was recommended for individuals between 4 and 6 years old. This study aims to assess the impact of routine varicella vaccination on the number and profile of hospitalized varicella patients during the single dose period, as well as in the first two years after the adoption of the second dose.

METHODS

An observational retrospective study was conducted in an infectious disease pediatric hospital, in Minas Gerais, Brazil. Clinical as well as epidemiological data from patients hospitalized due to varicella between 2010 and 2019 were collected. Patients were split into groups based on the vaccine introduction: pre-vaccine period, single dose and two-dose period. They were compared by age, sex, reason for admission, illness-related complications and clinical outcome.

RESULTS

There were 1193 admissions due to varicella during the studied period. When compared with the pre-vaccine period, the number of hospitalizations decreased in 61.5% during the single-dose regime, reaching 95.2% in the two-dose period. Hospitalization rates decreased in all age groups, including non-vaccinated individuals such as those younger than 12 months (92.1%). As for reasons of admission, secondary bacterial skin infections were perceived to be the most common cause (>70%). A reduction was also seen in admission of immunocompromised or HIV positive patients (84.8%).

CONCLUSION

The collected data shows a significant impact in the number of hospital admissions due to varicella after six years of the implementation of the vaccine, positively affecting both vaccinated and non-vaccinated individuals. Further reduction was seen after the second dose was initiated, but its true impact will only be understood fully after a longer period of continuous vaccination.

Incidence of varicella and herpes zoster after inclusion of varicella vaccine in national immunization schedule in Turkey: time trend study

The aim of the study was to investigate changes in the incidences of Varicella and Herpes Zoster (HZ) following introduction of single dose Varicella vaccine (VV) in Turkey. Changes in the incidences of varicella and HZ per 100,000 population were compared with pre (2011-2012) and post-VV period (2018-2019) throughout years between years 2011 and 2019 both for children and adults. In children ≤5 years of age, the annual incidences of varicella significantly decreased from 290 per 100000 children in 2011 to 24 per 100000 children in 2019 [p = .0001]. Also, for children ≤5 years the mean annual incidence of varicella decreased significantly [326/100000 ±51/100000 vs 23/100000 ± 1/100000; p = .014] between pre- and post-VV period. Moreover, the annual incidences of varicella significantly decreased from 43 per 100000 children in 2011 to 26 per 100000 children in 2019 in children age between 6 and 17 years. On the other hand, incidence of varicella in adult population (age >17 years) did not change significantly. Besides, the annual incidences of Herpes Zoster did not change significantly in children age stratas but significant increment observed in adult population. This increment was significant in adult age strata of 18-44 years, but non-significant in age strata of 45-64 years and >64 years. Thus, our study showed a significant reduction in the incidences of Varicella in children age stratas whereas significant increment in the incidence of HZ in adult population after the implementation of VV into the NIP of Turkey.

Incidence of varicella and herpes zoster after inclusion of varicella vaccine in national immunization schedule in Turkey: time trend study

The aim of the study was to investigate changes in the incidences of Varicella and Herpes Zoster (HZ) following introduction of single dose Varicella vaccine (VV) in Turkey. Changes in the incidences of varicella and HZ per 100,000 population were compared with pre (2011-2012) and post-VV period (2018-2019) throughout years between years 2011 and 2019 both for children and adults. In children ≤5 years of age, the annual incidences of varicella significantly decreased from 290 per 100000 children in 2011 to 24 per 100000 children in 2019 [p = .0001]. Also, for children ≤5 years the mean annual incidence of varicella decreased significantly [326/100000 ±51/100000 vs 23/100000 ± 1/100000; p = .014] between pre- and post-VV period. Moreover, the annual incidences of varicella significantly decreased from 43 per 100000 children in 2011 to 26 per 100000 children in 2019 in children age between 6 and 17 years. On the other hand, incidence of varicella in adult population (age >17 years) did not change significantly. Besides, the annual incidences of Herpes Zoster did not change significantly in children age stratas but significant increment observed in adult population. This increment was significant in adult age strata of 18-44 years, but non-significant in age strata of 45-64 years and >64 years. Thus, our study showed a significant reduction in the incidences of Varicella in children age stratas whereas significant increment in the incidence of HZ in adult population after the implementation of VV into the NIP of Turkey.

Spatiotemporal Epidemiology of Varicella in Chongqing, China, 2014-2018

Although immunization against varicella using vaccines has been proven to be significant and effective in the past decades, varicella remains a major public health concern for many developing countries. Varicella vaccination has not been introduced into routine immunization programs in China, and varicella outbreaks have continued to occur. Taking the city of Chongqing, which has a high prevalence of varicella, as an example, this study explored the spatiotemporal epidemiology of varicella. Based on the reported data of varicella cases from 1 January 2014 to 31 December 2018 in Chongqing, hot spots and space-time clusters of varicella were identified using spatial autocorrelation analysis and scan statistics. Within this period, a total of 112,273 varicella cases were reported in Chongqing (average annual incidence: 73.44 per 100,000), including one death. The incidence of varicella showed an increasing trend with significant seasonal peaks, which occurred during April to July and October to January of the following year. The total ratio of male to female patients affected was 1.10:1. Children under the age of 15 and students accounted for the majority of the patient population. The hotspots detected through local spatial autocorrelation analysis, and the most likely clusters identified by scan analysis, were primarily in the main urban districts of Chongqing. The secondary clusters were mostly detected in northeast and southwest Chongqing. There were obvious spatial dependence and spatiotemporal clustering characteristics of varicella in Chongqing from 2014 to 2018. High-risk districts, populations, and peak periods were found in this study, which could be helpful in implementing varicella prevention and control programs, and in adjusting vaccination strategies for the varicella vaccine based on actual conditions.

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.

Trends in varicella and mumps vaccination rates in children under 3 years of age in a tertiary children's hospital in Japan

BACKGROUND

In Japan, the voluntary vaccination rate is not known accurately. Although two doses of the measles and rubella vaccines have been part of the universal vaccine program since 2006, the varicella vaccine was added in October 2014 while the mumps vaccine still remains voluntary. The aim of this study was to evaluate trends in the live measles, rubella, varicella and mumps vaccination rates in Japan.

METHODS

This retrospective cohort study was conducted at Tokyo Metropolitan Children's Medical Center between October 2012 and December 2016. Patients aged 1-2 years who were admitted to the Department of General Pediatrics were enrolled. The trend in the vaccination rate against measles, rubella, varicella, and mumps was examined.

RESULTS

The measles and rubella vaccination rate was 80-90%. The varicella vaccination rate in the second quarter of 2012, the third quarter of 2014, and the fourth quarter of 2016 was 34.6%, 67.1%, and 80.7%, respectively. The mumps vaccination rate in the second quarter of 2012, the third quarter of 2014, and the fourth quarter of 2016 was 27.6%, 59.5%, and 61.8%, respectively.

CONCLUSIONS

The varicella and mumps vaccination rate improved until 2014 despite the fact that they were voluntary vaccinations. After varicella vaccination was added to the universal vaccination program, the varicella vaccination rate continued to improve. The mumps vaccination, which was not included, failed to improve, suggesting that the universal vaccination program contributed to increasing the uptake of the vaccines it includes.

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.

School, child care and camp exclusion policies for chickenpox: A rational approach

Widespread varicella vaccination in Canada since 2007 has changed the epidemiology of chickenpox, with a significant decline in varicella-related hospitalizations. However, there will always be a varicella-susceptible population because of immune-compromising treatments or conditions and/or parental vaccine refusal. This document updates and replaces a 1999 statement by the Canadian Paediatric Society. The CPS position on school and child care exclusion policies has not changed since the original statement, but because there have been two published reports of varicella outbreaks associated with summer camp attendance since 1999, this revision provides additional recommendations to mitigate risk for varicella transmission at summer camps.

Lessons From an Outbreak of Varicella Infection in Pediatric Hemato-oncology Patients

BACKGROUND

Immunocompromised patients exposed to varicella may experience significant morbidity and a 7% mortality rate. Management and outcome of an outbreak of varicella infection among hospitalized pediatric hemato-oncology patients using the guidelines of the American Academy of Pediatrics Committee on Infectious Diseases are presented.

METHODS

This retrospective study describes an outbreak of varicella infection between February 2011 and June 2011. Data were retrieved from the patients' files. Positive polymerase chain reaction results for varicella zoster virus from vesicular skin lesions were used for the diagnosis of varicella infection.

RESULTS

Twelve pediatric hemato-oncology patients experienced 13 episodes of varicella infection, 11 underwent 1 episode each and 1 patient had 2 episodes. All exposed patients without immunity received varicella zoster immune globulins or intravenous immunoglobulin and were isolated as recommended by the guidelines. Infected patients received intravenous acyclovir. One patient with acute lymphoblastic leukemia at induction chemotherapy died. All the other patients survived.

CONCLUSIONS

Our experience in the management of hospitalized immunocompromised patients exposed to varicella was that a positive IgG serology did not confer protection after exposure to varicella infection and thus can not serve as a marker for immunity. Unlike the isolation period sufficient for immunocompetent patients, crusted lesions can be contagious and thus require extended isolation for immunocompromised patients. Patients receiving rituximab are at greater risk of having persistent or recurrent disease. Studies with a larger sample size should be performed to better assess the management of immunocompromized patients exposed to varicella.

Chickenpox: An update

Despite its benign characteristics, chickenpox is a childhood disease responsible for complications and deaths, particularly in the high-risk population. VariZIG^®, not commercialized in France, is a good alternative for seronegative individuals exposed to the virus and not eligible for vaccination. The efficacy of routine vaccination has been demonstrated with a decrease in chickenpox incidence and with the development of herd immunity. Over time, the protective antibody titer of vaccinated people decreases and can be maintained by two doses of the vaccine. A tetravalent measles-mumps-rubella-chickenpox vaccine, used in the United States, has a good tolerability in spite of the occurrence of fever and febrile seizures. Routine vaccination would contribute to make savings in France, by reducing direct and indirect costs of chickenpox.

Early impact of universal varicella vaccination on childhood varicella and herpes zoster hospitalizations in Brazil

INTRODUCTION

The Brazilian childhood National Immunization Program (NIP) introduced live and attenuated varicella vaccination in a single dose, combined as tetraviral vaccine, at 15 months of age in the whole country, during September to December of 2013. The aim of this study was to report trends in incidence of childhood hospital admissions related to varicella and zoster in Brazil from 2003 to 2016, including the first three years after vaccine introduction.

METHODS

The number and incidence of hospital admission in patients aged less than 20 years in Brazilian public health system with an admission diagnosis of varicella and zoster from 2003 to 2016 were analyzed and pre (2003-2013) and post-vaccination periods (2014-2016) were compared. The data were obtained from DATASUS, a Brazilian government's open-access public health database system, and analyzed adjusting for secular trend and seasonality if a statistically significant change was found.

RESULTS

During the study period, 69,791 admissions due to varicella and herpes zoster occurred in the children younger than 20 years. After adjusting for seasonality, the incidence of hospitalizations decreased from 27.33 to 14.33 per 100000 per year, which corresponds to a reduction of 47.6% (95% confidence interval 18.19-77.04%, p < 0.001) in the vaccinated age group (1-4 years) in 2014-2016 compared to pre-vaccination period. The changes were not significant in the unvaccinated age groups.

CONCLUSION

The hospitalizations due to varicella and herpes zoster were decreased by half early after the introduction of a single dose of tetraviral vaccine in NIP in the vaccinated children. Further studies may assess duration and intensity of this effect, as well as the indirect effect in the unvaccinated age groups.

Varicella vaccination - the global experience

INTRODUCTION

Varicella, although a frequently benign childhood disease, nevertheless represents a considerable health burden. WHO recommends including varicella vaccines in universal routine vaccination programs, and maintaining coverage >80%. Many countries have successfully introduced varicella vaccination and have benefited from lower disease burden, but many others have not adopted the vaccine. Reasons include cost commitment for a 'mild childhood disease' or concerns that vaccination will shift varicella to older age groups or increase herpes zoster incidence. Areas covered: This literature review summarizes the effectiveness and epidemiological impact of varicella immunization programs. Expert commentary: Varicella vaccines are immunogenic with acceptable safety profiles. One and two dose schedules are highly effective against varicella and large reductions in disease incidence, particularly moderate-severe disease, have been widely reported. There is currently no evidence to suggest that the introduction of varicella vaccination results in a shift of varicella disease burden to older age groups. Although epidemiological studies have shown an increased incidence of herpes zoster since the vaccines were launched, there are many other contributing factors, and indeed, this secular trend was evident before their introduction. In conclusion, varicella vaccination easily fits into existing immunization programs and significantly reduces the often underestimated burden of varicella.

Preparing to introduce the varicella vaccine into the Italian immunisation programme: varicella-related hospitalisations in Tuscany, 2004-2012

A universal immunisation programme against varicella in the form of the measles-mumps-rubella-varicella (MMRV) vaccine for toddlers aged 13-15 months was introduced in Tuscany in July 2008. An assessment of the impact of this programme on varicella-related hospitalisations 4 years after its introduction could further support its adoption at a national level. The hospitalisation data were analysed in two periods: pre-vaccination (2004-2007) and vaccination period (2009-2012). The high coverage of the vaccines (84% in 2012) resulted in a significant decline in notifications, from 33,114 (2004-2007) to 13,184 cases (2009-2012), and also of hospitalisations, from 584 (pre-vaccination period) to 325 (vaccination period). The hospitalisation rate was 4.1 per 100,000 (95% confidence intervals (CI): 3.4-4.7) before the introduction of vaccination, which dropped to 2.2 per 100,000 (95% CI: 1.7-2.7) in the vaccination period (hospitalisation risk ratios: 0.54; 95% CI:  0.472-0.619). The reduction was most significant in the youngest age groups. The introduction of universal vaccination has already led to a significant decline in hospitalisations due to varicella after just 4 years of implementation. Hospitalisation rates fell noticeably among younger individuals involved in the vaccination programme. The decrease in hospitalisation rate in the older age groups suggests a possible indirect protection.

Prospective surveillance of hospitalisations associated with varicella in New Zealand children

AIM

Varicella is a vaccine-preventable disease not notifiable in New Zealand (NZ), and varicella vaccine is not funded in the National Immunisation Schedule (NIS). Hospitalisations can occur because of bacterial secondary infection and other complications, which can result in long-term sequelae. Varicella may not be acknowledged in discharge coding when complications occur weeks after infection. Using the New Zealand Paediatric Surveillance Unit (NZPSU), the aim of this study was to document the hospitalisation burden of this disease.

METHODS

Cases (0-14 years) of varicella and post-varicella complications requiring hospitalisation, including stroke syndromes where varicella occurred in the preceding 6 months, were notified to NZPSU between 1 November 2011 and 31 October 2013. Herpes zoster cases were excluded. Questionnaires were used to capture demographics, clinical features, management and short-term outcomes.

RESULTS

One hundred seventy-eight notifications were received and 144 were confirmed cases. Overall incidence was 8.3/100,000 children per year. Fifty-two percent were women with a median age of 2.4 years. Māori and Pacific Island (PI) children accounted for 74% of hospitalisations, with incidence rate ratios compared with European children of 2.8 and 3.9, respectively (P < 0.01). Complications included: infection (75%), respiratory (11%), neurological (11%), electrolyte disturbance (6%) and haemorrhagic varicella (4%). Nine percent were immunocompromised. Median duration of hospital admission was 4 days with 9% requiring intensive care admission. There were no reported deaths; however, 19% had ongoing problems at discharge.

CONCLUSION

Varicella has more associated morbidity than commonly perceived in immunocompetent children. Māori and PI children are more likely to have complications. This surveillance gives support for inclusion of universal varicella vaccine in the NZ NIS.

Hospitalization with varicella and shingles before and after introduction of childhood varicella vaccination in Germany

In Germany, one dose of varicella vaccination has been recommended for children aged <24 months since 2004, and 2 doses have been recommended since 2009. Vaccination coverage (VC) is above 80% for one dose and 60% for 2 doses. In this study, data on varicella- and shingles-associated hospitalizations before and after vaccine introduction were assessed. Based on ICD-coded data of the main diagnosis of hospitalized cases from 1995-2012 in Germany, annual age-adjusted and age-specific hospitalization incidences (cases/100,000; HI) were calculated. HI means 1995-2003 (pre-vaccination-period) versus 2005-2012 (post-vaccination-period) were compared. Age-specific trends and annual percentage change rates (APC) were assessed by joinpoint regression. Overall age-adjusted varicella-HI decreased from 3.3/100,000 pre-vaccination to 1.9/100,000 post vaccination. The decline was greatest in regions with the highest VC. The post-vaccination decline was greatest in children aged <1, 1-4, and 5-9 y, who had APCs of -18.2,-27.2 and -15.2, respectively, and significant joinpoints. In all other age groups no post-vaccination joinpoints were detected or they did not lead to a consistent trend. Age-adjusted shingles-HI increased from 8.8/100,000 (1995) to 16.8/100,000 (2012). Shingles-HI increased in all age groups with no significant post-vaccination joinpoints, except in children<1 and 1-4 y, where APCs of -5.6 and -3.6 were detected. Varicella vaccination significantly reduced varicella-HI in children below 10 y, but was not definitely related to varicella-HI in older age groups. A consistent increase of shingles-HI began before varicella vaccination was introduced and was not affected by vaccination.

A spot of bother: Why varicella vaccine programs matter

Objective

To evaluate Ontario's provincial varicella vaccination program through analysis of aggregate varicella cases in order to determine whether there has been a decrease in reportable disease burden; and to assess varicella vaccine adverse events following immunization (AEFIs).

Methods

Aggregate varicella cases (1993-2013) were extracted from the reportable disease databases. Pre-program (1993-2004) and post-program (2007-2013) periods were chosen according to implementation of the publicly funded vaccination program. AEFIs following administration of varicella vaccines (2010-2013) were also extracted. Reporting rates were calculated using net doses distributed as the denominator. Serious AEFIs were defined using World Health Organization standards.

Results

The incidence of aggregate varicella reports decreased significantly over the study period (from 311.4 to 22.2 cases per 100,000 population in 1993 and 2013, respectively). Incidence also decreased significantly in all age groups between the pre- and the post-program periods with a shift in age distribution towards older individuals in the post-program period. A total of 162 AEFIs following varicella vaccine were reported between 2010 and 2013 for an annualized reporting rate of 14.6 per 100,000 doses distributed. The most common events were rash (37.3%), including eight reports of varicella-like rash (0.7 per 100,000 doses distributed). Ten serious events were reported (0.9 per 100,000 doses distributed), and all vaccine recipients recovered.

Conclusion

Significant reductions in varicella disease incidence and low AEFI reporting rates were observed with the introduction of the publicly funded varicella vaccine program in Ontario. Continued surveillance is indicated to further assess trends in varicella disease and vaccine safety.

Twenty Years of Medically-Attended Pediatric Varicella and Herpes Zoster in Ontario, Canada: A Population-Based Study

OBJECTIVE

To determine if reductions in medically-attended pediatric varicella and herpes zoster occurred in Ontario, Canada, after publicly-funded varicella immunization was implemented in 2004.

METHODS

For fiscal years (FY) 1992-2011, we examined data on varicella and herpes zoster physician office visits, emergency department (ED) visits, hospitalizations (including for varicella-associated skin and soft tissue infections [SSTI]), and intensive care unit (ICU) admissions, among those aged <18 years. The pre-vaccine, privately-available, and vaccine program eras were FY1992-1998, FY1999-2003, and FY2004-2011, respectively. We used Poisson regressionand Kruskal-Wallis tests (all at the p<0.05 level of significance), and compared rates using incidence rate ratios (IRRs) and 95% confidence intervals (CIs).

RESULTS

Incidence of varicella office visits declined over the study period from a high of 25.1/1,000 in FY1994 to a low of 3.2/1,000 in FY2011. ED visits and hospitalizations followed similar patterns of decreasing rates later in the study period. IRRs comparing the vaccine program versus pre-vaccine eras were 0.29 (95%CI: 0.26-0.32) for office visits, 0.29 (95%CI: 0.21-0.40) for ED visits, and 0.41 (95%CI: 0.10-1.69) for hospitalizations. Annual declines in varicella office visits were 7.7%, 9.1%, 8.4%, and 8.4% per year among children aged <1 year, 1-4 years, 5-11 years, and ≥12 years, respectively (all p<0.001). Age-specific rates of varicella-associated SSTI declined significantly among children <12 years (p<0.001) and rates of ICU admissions decreased significantly for children <1 year (p = 0.02). (p<0.001) over the study period. For children aged 5-17 years, herpes zoster office visits decreased whereas ED visits increased (both p<0.001) and there was a small, non-significant (p = 0.07), decrease in hospitalizations.

CONCLUSION

Medically-attended varicella decreased during the study period, particularly since varicella vaccine was publicly-funded. Results suggest immunization program-related changes in varicella epidemiology, including herd effects, demonstrated by reductions in varicella in program-ineligible age groups. We did not observe a consistent impact on herpes zoster.

Development of malaria transmission-blocking vaccines: from concept to product

Despite decades of effort battling against malaria, the disease is still a major cause of morbidity and mortality. Transmission-blocking vaccines (TBVs) that target sexual stage parasite development could be an integral part of measures for malaria elimination. In the 1950s, Huff et al. first demonstrated the induction of transmission-blocking immunity in chickens by repeated immunizations with Plasmodium gallinaceum-infected red blood cells. Since then, significant progress has been made in identification of parasite antigens responsible for transmission-blocking activity. Recombinant technologies accelerated evaluation of these antigens as vaccine candidates, and it is possible to induce effective transmission-blocking immunity in humans both by natural infection and now by immunization with recombinant vaccines. This chapter reviews the efforts to produce TBVs, summarizes the current status and advances and discusses the remaining challenges and approaches.

Laboratory investigations of vaccinated patients with varicella

BACKGROUND

Accompanying varicella vaccination in children in Germany recommended with one (2004) and two (2009) doses, sentinel surveillance of varicella with a sample (n∼900) of private physicians was established in 2005. Physicians reported monthly aggregated data on all varicella cases and case-based on vaccinated patients, of whom skin lesion samples were laboratory investigated to identify varicella-zoster virus (VZV). We analyzed the impact of vaccination frequency on the number of cases and on laboratory results within the sentinel.

METHODS

Swabs were obtained with a Teflon tip and sent together with a case-based questionnaire to the reference laboratory. VZV wild-type and vaccine-type was identified by polymerase chain-reaction (PCR) and pyrosequencing methods. Case-based data and laboratory results were analyzed descriptively.

RESULTS

From April 2005 to March 2014, of all monthly reported cases (n=111,456) 4789 were vaccinated and eligible for further analysis. No differences were found between laboratory investigated and not investigated cases (1017 vs. 3772) except that the proportion of cases vaccinated twice was higher in lab-cases (29.4% vs. 16.1%). PCR remained negative in 69.6% (197/283) of breakthrough-cases vaccinated twice, in comparison to 22.7% (147/649) breakthrough-cases vaccinated once. VZV was confirmed in 500 (81) patients with breakthrough varicella after one (two) vaccination(s); identification of VZV wild-type, vaccine-type, or no further differentiation was possible in 485 (72), 5 (6), and 10 (3) cases, respectively.

CONCLUSION

Varicella breakthrough disease is rare in Germany and suspected clinical cases require laboratory confirmation. The lower confirmation rate of VZV after two vaccine doses suggests a better protection compared to one dose.

Varicella vaccination programs do not seem to shift the age of disease to older age groups

The paper of Baxter et al., recently published in Pediatrics show through five cross-sectional studies, a high impact of vaccination in the decline of varicella incidence and hospitalizations in all age groups in the United States between 1995 and 2009. As a consequence of herd immunity, varicella incidence has also diminished in those non vaccinated, which indicates no shift in the burden of varicella to older age groups.

Control of varicella in the post-vaccination era in Australia: a model-based assessment of catch-up and infant vaccination strategies for the future

In Australia, varicella vaccine was universally funded in late 2005 as a single dose at 18 months. A school-based catch-up programme for children aged 10-13 years without a history of infection or vaccination was funded until 2015, when those eligible for universal infant vaccination would have reached the age of high school entry. This study projects the impact of discontinuing catch-up vaccination on varicella and zoster incidence and morbidity using a transmission dynamic model, in comparison with alternative policy options, including two-dose strategies. At current vaccine coverage (83% at 2 years and 90% at 5 years), ceasing the adolescent catch-up programme in 2015 was projected to increase varicella-associated morbidity between 2035 and 2050 by 39%. Although two-dose infant programmes had the lowest estimated varicella morbidity, the incremental benefit from the second dose fell by 70% if first dose coverage increased from 83% to 95% by age 24 months. Overall zoster morbidity was predicted to rise after vaccination, but differences between strategies were small. Our results suggest that feasibility of one-dose coverage approaching 95% is an important consideration in estimating incremental benefit from a second dose of varicella vaccine.

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.