Impact of the Maturing Varicella Vaccination Program on Varicella and Related Outcomes in the United States: 1994-2012

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.

Syndromic Surveillance as a Tool for Case-Based Varicella Reporting in Georgia, 2016-2019

OBJECTIVES

Syndromic surveillance can be used to enhance notifiable disease case-based surveillance. We analyzed features of varicella reported in Georgia to evaluate case detection through syndromic surveillance and to compare varicella reported through syndromic surveillance with varicella reported from all other sources.

METHODS

Syndromic surveillance was incorporated into case-based varicella surveillance by the Georgia Department of Public Health (GDPH) in May 2016. A cross-sectional study design evaluated syndromic and nonsyndromic varicella reported to GDPH from May 1, 2016, through December 31, 2019. Varicella was reported by nonsyndromic sources including health care providers, schools, and laboratories. We identified syndromic varicella cases from urgent care and emergency department visit data with discharge diagnoses containing the terms "varicella" or "chickenpox."

RESULTS

Syndromic notifications accounted for 589 of 2665 (22.1%) suspected varicella reports investigated by GDPH. The positive predictive value was 33.1% for syndromic notifications and 31.3% for nonsyndromic notifications. Mean days from rash onset to GDPH notification was 3.2 days fewer (P < .001) among patients identified through syndromic notification than among patients identified through nonsyndromic notification. The odds of varicella identified by syndromic notification being outbreak-associated were 0.18 (95% CI, 0.09-0.36) times those of varicella identified through nonsyndromic notification.

PRACTICE IMPLICATIONS

Syndromic notifications were an effective, timely means for varicella case detection. Syndromic patients were significantly less likely than nonsyndromic patients to be outbreak-associated, possibly because of early detection. Syndromic surveillance enhanced case-based reporting for varicella in Georgia and was a useful tool to improve notifiable disease surveillance.

The Impact of Universal Varicella Vaccination on Herpes Zoster Incidence in the United States: Comparison of Birth Cohorts Preceding and Following Varicella Vaccination Program Launch

When the US varicella vaccination program was introduced in 1995, its impacts on the epidemiology of herpes zoster (HZ) were not precisely known. We used a large claims database to examine HZ incidence in the US during 1998-2019 among persons aged ≥30 years (the prevaccine cohort, born before 1990), and aged 1-29 years (includes the postvaccine cohort, born since 1990). We defined incident HZ as the first instance of an outpatient or emergency department (ED) claim with an HZ diagnostic code. Additionally, we examined the proportion of HZ visits among all ED visits as a complementary method to assess for healthcare-seeking artifacts in the findings. In persons aged ≥30 years (prevaccine cohort), we observed age-specific increases in HZ incidence during the earlier study years, with decelerations in later years, starting in 2007 with oldest age groups. Similar patterns were seen when we examined HZ visits as a proportion of all ED visits. For persons aged 1-29 years, age-specific HZ incidence increased early in the study period for the oldest age groups who were born prevaccine, but later declined in a stepwise pattern once each age group was comprised of persons born in the postvaccine period. Our results, corroborated with previously published studies, do not support prior modeling predictions that the varicella vaccination program would increase HZ incidence among adult cohorts who previously experienced varicella. Our findings also suggest that continued declines in age-specific HZ incidence as varicella-vaccinated cohorts age are likely.

Health and Economic Impact of the United States Varicella Vaccination Program, 1996-2020

BACKGROUND

The aim of this study was to evaluate the health and economic impact of the varicella vaccination program on varicella disease in the United States (US), 1996-2020.

METHODS

Analysis was conducted using the Centers for Disease Control and Prevention or published annual population-based varicella incidence, and varicella-associated hospitalization, outpatient visit, and mortality rates in the US population aged 0-49 years during 1996-2020 (range, 199.5-214.2 million persons) compared to before vaccination (1990-1994). Disease costs were estimated using the societal perspective. Vaccination program costs included costs of vaccine, administration, postvaccination adverse events, and travel and work time lost to obtain vaccination. All costs were adjusted to 2020 US dollars using a 3% annual discount rate. The main outcome measures were the number of varicella-associated cases, hospitalizations, hospitalization days, and premature deaths prevented; life-years saved; and net societal savings from the US varicella vaccination program.

RESULTS

Among US persons aged 0-49 years, during 1996-2020, it is estimated that more than 91 million varicella cases, 238 000 hospitalizations, 1.1 million hospitalization days, and almost 2000 deaths were prevented and 118 000 life-years were saved by the varicella vaccination program, at net societal savings of $23.4 billion.

CONCLUSIONS

Varicella vaccination has resulted in substantial disease prevention and societal savings for the US over 25 years of program implementation.

Impact of universal varicella vaccination on the use and cost of antibiotics and antivirals for varicella management in the United States

Background

Our objective was to estimate the impact of universal varicella vaccination (UVV) on the use and costs of antibiotics and antivirals for the management of varicella among children in the United States (US).

Methods

A decision tree model of varicella vaccination, infections and treatment decisions was developed. Results were extrapolated to the 2017 population of 73.5 million US children. Model parameters were populated from published sources. Treatment decisions were derived from a survey of health care professionals’ recommendations. The base case modelled current vaccination coverage rates in the US with additional scenarios analyses conducted for 0%, 20%, and 80% coverage and did not account for herd immunity benefits.

Results

Our model estimated that 551,434 varicella cases occurred annually among children ≤ 18 years in 2017. Antivirals or antibiotics were prescribed in 23.9% of cases, with unvaccinated children receiving the majority for base case. The annual cost for varicella antiviral and antibiotic treatment was approximately $14 million ($26 per case), with cases with no complications accounting for $12 million. Compared with the no vaccination scenario, the current vaccination rates resulted in savings of $181 million (94.7%) for antivirals and $78 million (95.0%) for antibiotics annually. Scenario analyses showed that higher vaccination coverage (from 0% to 80%) resulted in reduced annual expenditures for antivirals (from $191 million to $41 million), and antibiotics ($82 million to $17 million).

Conclusions

UVV was associated with significant reductions in the use of antibiotics and antivirals and their associated costs in the US. Higher vaccination coverage was associated with lower use and costs of antibiotics and antivirals for varicella management.

Immune Responses to Varicella-Zoster Virus Vaccines

The live attenuated varicella vaccine is intended to mimic the tempo and nature of the humoral and cell-mediated immune responses to varicella infection. To date, two doses of varicella vaccine administered in childhood have been very effective in generating varicella-zoster virus (VZV) immune responses that prevent natural infection for at least several decades. After primary infection, the infecting VZV establishes latency in sensory and cranial nerve ganglia with the potential to reactivate and cause herpes zoster. Although, the immune responses developed during varicella are important for preventing herpes zoster they wane with increasing age (immune senescence) or with the advent of immune suppression. Protection can be restored by increasing cell-mediated immune responses with two doses of an adjuvanted recombinant VZV glycoprotein E vaccine that stimulates both VZV-and gE-specific immunity. This vaccine provides ~85-90% protection against herpes zoster for 7-8 years (to date).

Herpes Zoster and Postherpetic Neuralgia: Changing Incidence Rates From 1994 to 2018 in the United States

BACKGROUND

The incidence of herpes zoster (HZ) has been increasing in recent decades. Although 2 vaccines for HZ are available, there have been few studies on the incidence rates of HZ and postherpetic neuralgia (PHN) since their introduction. This study examined the incidence rates of HZ and PHN from 1994 to 2018 in the United States to determine if they have continued to increase since introduction of the HZ vaccines.

METHODS

A de-identified longitudinal administrative claims database, the OptumLabs Data Warehouse, was used to assess incidence rates among individuals continuously enrolled in the database for ≥365 days with no prior history of HZ or PHN. Unstandardized and standardized incidence rates were calculated by year, 10-year age groups, sex, and race/ethnicity.

RESULTS

There were 610 766 individuals with HZ (median age, 56.3; interquartile range, 43.0-68.7 years; 59.8% women; 70.6% white). From 1994 to 2018, the incidence of HZ increased from 286.0 (95% confidence interval [CI], 259.1-312.8) to 579.6 (95% CI, 554.2-605.0) cases per 100 000 person-years, an annual increase of 3.1% (95% CI, 2.5-3.6%). Since 2007, annual HZ incidence rates have decreased in individuals ≤20 and >60 years old. The overall incidence rate of PHN was 57.5 (95% CI, 56.0-59.0) cases per 100 000 person-years. The proportion of individuals with HZ who developed PHN was higher from 2007 to 2018 than from 1994 to 2006.

CONCLUSIONS

HZ incidence rates have continued to increase in age groups for which HZ vaccines are not currently recommended, warranting a review of current vaccine recommendations.

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.

Pox Parties for Grannies? Chickenpox, Exogenous Boosting, and Harmful Injustices

Some societies tolerate or encourage high levels of chickenpox infection among children to reduce rates of shingles among older adults. This tradeoff is unethical. The varicella zoster virus (VZV) causes both chickenpox and shingles. After people recover from chickenpox, VZV remains in their nerve cells. If their immune systems become unable to suppress the virus, they develop shingles. According to the Exogenous Boosting Hypothesis (EBH), a person's ability to keep VZV suppressed can be 'boosted' through exposure to active chickenpox infections. We argue that even if this hypothesis were true, immunization policies that discourage routine childhood varicella vaccination in order to prevent shingles for other people are unethical. Such policies harm children and treat them as mere means for the benefit of others, and are inconsistent with how parents should treat their children and physicians should treat their patients. These policies also seem incompatible with institutional transparency.

The Epidemiology of Herpes Zoster in the United States During the Era of Varicella and Herpes Zoster Vaccines: Changing Patterns Among Children

Varicella vaccination can have complex direct and indirect influences on the epidemiology of herpes zoster among children. We evaluated pediatric herpes zoster trends using administrative databases. The incidence has declined in a step-wise pattern since the varicella vaccination program's introduction, suggesting that rates may eventually decline in the entire population.

Varicella seroepidemiology and immunization in a cohort of future healthcare workers in the pre-vaccination era

OBJECTIVES

The goal of this study was to establish the seroprevalence of positive antibodies against varicella and compliance with varicella vaccination in the pre-vaccination era.

METHODS

A cohort of 10 683 Italian students from Padua University Medical School (from 2004 to 2019) were enrolled and classified as unvaccinated, vaccinated once, or vaccinated twice against varicella, according to their vaccination certificate. The antibody titre was measured and the seroprevalence of positive subjects was determined. Subjects with negative or equivocal antibodies were invited for vaccination, and then the antibody titre was retested.

RESULTS

Unvaccinated students were mostly seropositive (95.6%), compared with vaccinated students who were less seropositive (68.0% after one dose and 78.6% after two doses) and had significantly lower antibody titres (p < 0.0001). The post-test vaccination had a positive response rate of 85.4%: 67.4% after one dose and 91.4% after two doses.

CONCLUSIONS

In the pre-vaccination era, only 3.3% of future healthcare workers were vaccinated against varicella (1.1% once and 2.2% twice). Vaccination or revaccination of negative and equivocal individuals could reduce the number of susceptible people. Implementation of varicella vaccine (two doses) in healthcare workers is of primary importance to reduce the risk of transmission.

Varicella-zoster virus post-exposure management and prophylaxis: A review

Varicella-zoster virus causes both varicella (chickenpox) and herpes zoster (shingles). Although varicella incidence has dramatically declined since introduction of the live-attenuated varicella vaccine, vaccination rates are suboptimal, and outbreaks still occur. Additionally, herpes zoster incidence continues to rise. Severe or fatal complications may result from varicella transmission to at-risk individuals who are exposed to either varicella or herpes zoster. An increasing number of children and adults are receiving immunosuppressive therapies and are at high risk for severe varicella and other complications if exposed to the virus. Clinical management of individuals exposed to varicella-zoster virus should take into consideration the type of exposure, evidence of immunity, and host-immune status with regard to ability to receive varicella vaccination safely. Post-exposure varicella vaccination may prevent infection or mitigate disease severity in persons eligible for vaccination. Post-exposure prophylaxis with varicella zoster immune globulin is indicated for populations ineligible for vaccination, including immunocompromised children and adults, pregnant women, newborns of mothers with varicella shortly before or after delivery, and premature infants. Appropriate post-exposure management of individuals exposed to either varicella or herpes zoster-including assessment of immune status and rapid provision of optimal prophylaxis-can help avoid potentially devastating complications of varicella-zoster virus infection.

Transmission of Vaccine-Strain Varicella-Zoster Virus: A Systematic Review

CONTEXT

Live vaccines usually provide robust immunity but can transmit the vaccine virus.

OBJECTIVE

To assess the characteristics of secondary transmission of the vaccine-strain varicella-zoster virus (Oka strain; vOka) on the basis of the published experience with use of live varicella and zoster vaccines.

DATA SOURCES

Systematic review of Medline, Embase, the Cochrane Library, Cumulative Index to Nursing and Allied Health Literature, and Scopus databases for articles published through 2018.

STUDY SELECTION

Articles that reported original data on vOka transmission from persons who received vaccines containing the live attenuated varicella-zoster virus.

DATA EXTRACTION

We abstracted data to describe vOka transmission by index patient's immune status, type (varicella or herpes zoster) and severity of illness, and whether transmission was laboratory confirmed.

RESULTS

Twenty articles were included. We identified 13 patients with vOka varicella after transmission from 11 immunocompetent varicella vaccine recipients. In all instances, the vaccine recipient had a rash: 6 varicella-like and 5 herpes zoster. Transmission occurred mostly to household contacts. One additional case was not considered direct transmission from a vaccine recipient, but the mechanism was uncertain. Transmission from vaccinated immunocompromised children also occurred only if the vaccine recipient developed a rash postvaccination. Secondary cases of varicella caused by vOka were mild.

LIMITATIONS

It is likely that other vOka transmission cases remain unpublished.

CONCLUSIONS

Healthy, vaccinated persons have minimal risk for transmitting vOka to contacts and only if a rash is present. Our findings support the existing recommendations for routine varicella vaccination and the guidance that persons with vaccine-related rash avoid contact with susceptible persons at high risk for severe varicella complications.

Varicella Virus Vaccine Live: A 22-Year Review of Postmarketing Safety Data

Background

Varicella, a contagious infectious disease caused by varicella zoster virus (VZV), can result in hospitalization and, occasionally, death. Varicella virus vaccine live (VVVL [VARIVAX]) was introduced in the United States in 1995.

Methods

This comprehensive review of the VVVL safety profile is based on 22 years of postmarketing adverse event (AE) data received through spontaneous and noninterventional study reports submitted by health care providers and on a review of the published literature (cumulatively from March 17, 1995, through March 16, 2017, during which period >212 million doses were distributed globally).

Results

The VVVL safety profile was consistent with previous publications, with common AEs including varicella, rash, and pyrexia. AE reports have decreased over time, from ~500 per million doses in 1995 to ~40 per million doses in 2016; serious AEs comprise 0.8 reports per million doses. Secondary transmission was rare (8 confirmed cases); polymerase chain reaction analysis indicated that 38 of the 66 reported potential secondary transmission cases of varicella were attributable to wild-type VZV. The prevalence of major birth defects in the Pregnancy Registry was similar to that in the general US population. In total, 86 cases of death were reported after vaccination with VVVL; immunocompromised individuals appeared to be most at risk for a fatal varicella- or herpes zoster–related outcome.

Conclusions

This comprehensive 22-year review confirms the overall safety profile for VVVL, with no new safety concerns identified. Since VVVL’s introduction in 1995, notable declines in varicella cases and in varicella-related deaths have occurred compared with the prevaccination period.

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.

Clinical Features of Varicella-Zoster Virus Infection

Varicella-zoster virus (VZV) is a pathogenic human herpes virus that causes varicella (chickenpox) as a primary infection, following which it becomes latent in peripheral ganglia. Decades later, the virus may reactivate either spontaneously or after a number of triggering factors to cause herpes zoster (shingles). Varicella and its complications are more severe in the immunosuppressed. The most frequent and important complication of VZV reactivation is postherpetic neuralgia, the cause of which is unknown and for which treatment is usually ineffective. Reactivation of VZV may also cause a wide variety of neurological syndromes, the most significant of which is a vasculitis, which is treated with corticosteroids and the antiviral drug acyclovir. Other VZV reactivation complications include an encephalitis, segmental motor weakness and myelopathy, cranial neuropathies, Guillain–Barré syndrome, enteric features, and zoster sine herpete, in which the viral reactivation occurs in the absence of the characteristic dermatomally distributed vesicular rash of herpes zoster. There has also been a recent association of VZV with giant cell arteritis and this interesting finding needs further corroboration. Vaccination is now available for the prevention of both varicella in children and herpes zoster in older individuals.

Update on trends in varicella mortality during the varicella vaccine era-United States, 1990-2016

We reported previously that the annual average mortality rate in the United States in 2008-2011 for varicella listed as the underlying cause declined 87% compared with the prevaccine period (1990-1994). Here, we update the analysis with five additional years of data. We used varicella death data from the 2012-2016 Mortality Multiple Cause-of Death records to calculate mortality rates during 2012-2016 and trends since the prevaccine period and end of 1-dose vaccination program (2005-2007). The annual average age-adjusted mortality rate for varicella as the underlying cause was 0.03 per million population during 2012-2016, a 94% reduction from prevaccine years and a 47% reduction from 2005-2007. Varicella deaths continue to decline due to the varicella vaccination program in the United States.

Varicella Vaccination Among US Adolescents: Coverage and Missed Opportunities, 2007-2014

CONTEXT

Since 2007, 2 doses of varicella vaccine have been routinely recommended, with a catch-up second dose recommended for those who received only 1 prior dose.

OBJECTIVE

To examine varicella vaccination coverage with 2 or more doses and the proportions of adolescents with evidence of immunity to varicella (≥2 doses of vaccine or varicella history) during 2007-2014. To assess timing of second-dose receipt, factors associated with 2 or more vaccine doses, and missed second-dose opportunities during 2014.

DESIGN, SETTING, AND PARTICIPANTS

We used data from the 2007-2014 National Immunization Survey-Teen (NIS-Teen), which collects information on adolescents aged 13 to 17 years in the United States.

RESULTS

From 2007 to 2014, varicella vaccination coverage with 2 or more doses increased from 8.3% to 66.9% in 13- to 15-year-olds and from 3.6% to 56.7% in 16- to 17-year-olds. The proportions with evidence of immunity also increased from 68.0% to 84.1% (13- to 15-year-olds) and 78.6% to 83.4% (16- to 17-year-olds). In 2014, 13.4% of 13- to 15-year-olds and 3.2% of 16- to 17-year-olds had received their second dose at 4 to 6 years of age. Factors most significantly associated with lower coverage with 2 or more doses were not having an 11- to 12-year well-child visit, not receiving an adolescent vaccine, and residence in a state with no 2-dose immunization school entry requirement. Seventy-seven percent of 1-dose vaccinated adolescents had 1 or more missed opportunities to receive their second dose; if were they not missed, 2-dose coverage would have increased from 79.5% to 94.8%.

CONCLUSIONS

Levels of varicella vaccination coverage with 2 or more doses and the proportion of adolescents with evidence of immunity increased from 2007 to 2014, though 16% lacked evidence of immunity in 2014. Although catch-up campaigns have succeeded, missed vaccination opportunities persist.

Varicella Virus Vaccination in the United States

Varicella zoster virus (VZV) is the cause of chickenpox (varicella) and shingles (zoster), and was once responsible for over 4 million infections in the United States annually. The development of a live attenuated VZV vaccine was initially viewed with extreme skepticism. Nonetheless, a VZV vaccine was developed in the 1970s by Takahashi and his colleagues in Japan and was eventually licensed in the US. It is now known to be one of the safest and most effective vaccines available and is administered worldwide. Here are described important factors that contributed to the successful research and licensure of the highly successful VZV vaccine.

Post-varicella Arterial Ischemic Stroke in Denmark 2010 to 2016

BACKGROUND

Varicella, most often a benign disease of childhood, is associated with an increased risk of arterial ischemic stroke in children. The aim of the present study was to estimate the incidence of post-varicella arterial ischemic stroke in the Danish child population and describe clinical characteristics of children admitted with post-varicella arterial ischemic stroke.

METHODS

In the Danish National Patient Register, we identified inpatients 28 days to 16 years of age with a discharge diagnosis of stroke or cerebrovascular disease from 2010 to 2016. Medical files were reviewed, and children with arterial ischemic stroke and varicella infection less than 12 months before onset of symptoms were included.

RESULTS

We identified 15 children with arterial ischemic stroke and varicella less than 12 months before. In nine children, the diagnosis was confirmed by detection of varicella zoster virus DNA or varicella zoster virus immunoglobulin G in the cerebrospinal fluid. All children were previously healthy, the mean age was four years, and 67% were male. The median time from varicella rash to arterial ischemic stroke was 4.6 months. The most common location of arterial ischemic stroke was the basal ganglia, and affected vessels were most often in the anterior circulation. Fifty-three percent experienced neurological sequelae of varying degree.

CONCLUSIONS

In Denmark, where varicella vaccination is not part of the childhood vaccination program, the estimated risk of post-varicella arterial ischemic stroke was one case (including possible cases) per 26,000 children with varicella.

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.

One or two doses of live varicella virus-containing vaccines: Efficacy, persistence of immune responses, and safety six years after administration in healthy children during their second year of life

BACKGROUND

This phase III B follow-up of an initial multicenter study (NCT00226499) will evaluate the ten-year efficacy of two doses of the combined measles-mumps-rubella-varicella vaccine (MMRV) and one dose of the live attenuated varicella vaccine (V) versus a measles-mumps-rubella control group (MMR) for the prevention of clinical varicella disease. Here we present efficacy results for six years post-vaccination.

METHODS

In phase A of the study, healthy children aged 12-22 months from ten European countries were randomized (3:3:1) and received either two doses of MMRV, or one dose of combined MMR and one dose of monovalent varicella vaccine (MMR+V), or two doses of the MMR vaccine (control), 42 days apart. Vaccine efficacy against all and against moderate or severe varicella (confirmed by detection of viral DNA or epidemiological link) was assessed from six weeks up to six years post-dose 2 for the MMRV and MMR+V groups, and was calculated with 95% confidence intervals (CI). The severity of varicella was calculated using the modified Vázquez scale (mild ≤ 7; moderately severe = 8-15; severe ≥ 16). Herpes zoster cases were also recorded.

RESULTS

5289 children (MMRV = 2279, mean age = 14.2, standard deviation [SD] = 2.5; MMR+V = 2266, mean age = 14.2, SD = 2.4; MMR = 744, mean age = 14.2, SD = 2.5 months) were included in the efficacy cohort. 815 varicella cases were confirmed. Efficacy of two doses of MMRV against all and against moderate or severe varicella was 95.0% (95% CI: 93.6-96.2) and 99.0% (95% CI: 97.7-99.6), respectively. Efficacy of one dose of varicella vaccine against all and against moderate or severe varicella was 67.0% (95% CI: 61.8-71.4) and 90.3% (95% CI: 86.9-92.8), respectively. There were four confirmed herpes zoster cases (MMR+V = 2, MMR = 2), all were mild and three tested positive for the wild-type virus.

CONCLUSIONS

Two doses of the MMRV vaccine and one dose of the varicella vaccine remain efficacious through six years post-vaccination.

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.

Laboratory Diagnosis of Breakthrough Varicella in Children

BACKGROUND

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

SUBJECTS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Impact and effectiveness of childhood varicella vaccine program in Queensland, Australia

BACKGROUND

In November 2005, Australia introduced a publicly funded single dose of varicella vaccine for children aged 18-months. We describe the impact of this program on varicella hospitalisations in Queensland and provide the first assessment of single-dose varicella vaccine effectiveness in Australia since the program commenced.

METHODS

Age-standardised varicella hospitalisation rates were calculated for 2000-2014 and pre- and post-public funding period rates compared. Case-control studies were conducted to investigate the association between vaccine receipt and both varicella hospitalisations and uncomplicated varicella emergency department presentations. Cases were matched to controls from a population-based register by date of birth and state of residence. Vaccine effectiveness was calculated as (1-odds ratio)×100%.

RESULTS

Compared to the pre-funded period (2000-2003), age-standardised varicella hospitalisation rates declined by more than 70% in 2011-2014 with varicella principal diagnosis rates declining from 5.7 to 1.6 per 100,000 population per year. Varicella vaccine effectiveness at preventing hospitalisation with a principal diagnosis of varicella among children aged 19-months to 6-years was 81.9% (95% confidence interval: 61.8-91.4%), while for emergency department presentations among children aged 19-months to 8-years it was 57.9% (95% confidence interval: 48.5-65.5%).

CONCLUSIONS

In Australia, the single-dose varicella vaccination program has substantially reduced varicella morbidity. The single-dose varicella vaccine schedule is moderately-to-highly effective against hospitalisation, but appears less effective against emergency department presentations.

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.

Impact of Type I Interferon on the Safety and Immunogenicity of an Experimental Live-Attenuated Herpes Simplex Virus 1 Vaccine in Mice

Viral fitness dictates virulence and capacity to evade host immune defenses. Understanding the biological underpinnings of such features is essential for rational vaccine development. We have previously shown that the live-attenuated herpes simplex virus 1 (HSV-1) mutant lacking the nuclear localization signal (NLS) on the ICP0 gene (0ΔNLS) is sensitive to inhibition by interferon beta (IFN-β) in vitro and functions as a highly efficacious experimental vaccine. Here, we characterize the host immune response and in vivo pathogenesis of HSV-1 0ΔNLS relative to its fully virulent parental strain in C57BL/6 mice. Additionally, we explore the role of type 1 interferon (IFN-α/β) signaling on virulence and immunogenicity of HSV-1 0ΔNLS and uncover a probable sex bias in the induction of IFN-α/β in the cornea during HSV-1 infection. Our data show that HSV-1 0ΔNLS lacks neurovirulence even in highly immunocompromised mice lacking the IFN-α/β receptor. These studies support the translational viability of the HSV-1 0ΔNLS vaccine strain by demonstrating that, while it is comparable to a virulent parental strain in terms of immunogenicity, HSV-1 0ΔNLS does not induce significant tissue pathology.IMPORTANCE HSV-1 is a common human pathogen associated with a variety of clinical presentations ranging in severity from periodic "cold sores" to lethal encephalitis. Despite the consistent failures of HSV subunit vaccines in clinical trials spanning the past 28 years, opposition to live-attenuated HSV vaccines predicated on unfounded safety concerns currently limits their widespread acceptance. Here, we demonstrate that a live-attenuated HSV-1 vaccine has great translational potential.

Safety of Second-Dose Single-Antigen Varicella Vaccine

BACKGROUND AND OBJECTIVE

In 2006, routine 2-dose varicella vaccination for children was recommended to improve control of varicella. We assessed the safety of second-dose varicella vaccination.

METHODS

We identified second-dose single-antigen varicella vaccine reports in the Vaccine Adverse Event Reporting System during 2006 to 2014 among children aged 4 to 18 years. We analyzed reports by age group (4-6 and 7-18 years), sex, serious or nonserious status, most common adverse events (AEs), and whether other vaccines were administered concomitantly with varicella vaccine. We reviewed serious reports of selected AEs and conducted empirical Bayesian data mining to detect disproportional reporting of AEs.

RESULTS

We identified 14 641 Vaccine Adverse Event Reporting System reports after second-dose varicella vaccination, with 494 (3%) classified as serious. Among nonserious reports, injection site reactions were most common (48% of children aged 4-6 years, 38% of children aged 7-18 years). The most common AEs among serious reports were pyrexia (31%) for children aged 4 to 6 years and headache (28%) and vomiting (27%) for children aged 7 to 18 years. Serious reports of selected AEs included anaphylaxis (83), meningitis (5), encephalitis (16), cellulitis (52), varicella (6), herpes zoster (6), and deaths (7). One immunosuppressed adolescent was reported with vaccine-strain herpes zoster. Only previously known AEs were reported more frequently after second-dose varicella vaccination compared with other vaccines.

CONCLUSIONS

We identified no new or unexpected safety concerns for second-dose varicella vaccination. Robust safety monitoring remains an important component of the national varicella vaccination program.

Epidemiology of Varicella During the 2-Dose Varicella Vaccination Program - United States, 2005-2014

Before availability of varicella vaccine in the United States, an estimated 4 million varicella cases, 11,000-13,500 varicella-related hospitalizations, and 100-150 varicella-related deaths occurred annually. The varicella vaccination program was implemented in the United States in 1996 as a 1-dose routine childhood program. Based on data from two varicella active surveillance sites, the varicella vaccination program led to 90% decline in incidence over the next decade (1). However, because of continued varicella outbreaks, a routine 2-dose schedule (at ages 12-15 months and 4-6 years) was recommended and has been in place since 2006 (2). The declines in incidence (1,3-6) made it feasible for states to implement varicella case-based surveillance and to report varicella data to CDC through the National Notifiable Diseases Surveillance System (NNDSS). State data have become the primary source for monitoring trends in varicella incidence nationally (7). Using NNDSS data, CDC previously reported nationwide declines in varicella incidence of 72% from the end of the 1-dose to the early years of the 2-dose varicella vaccination program (2006-2010) (7). This report updates varicella incidence trends to include the most recent years in the 2-dose varicella vaccination program. Between the period 2005-2006 (before the 2-dose recommendation) and 2013-2014, overall varicella incidence declined 84.6%, with the largest declines reported in children aged 5-9 years (89.3%) and 10-14 years (84.8%). The availability of varicella-specific data varied over time. During the last 2 years examined (2013 and 2014), completeness of reporting of two critical variables monitored by CDC, vaccination status (receipt of at least 1 dose of varicella vaccine) of cases and severity of disease based on number of lesions, were 54.2% and 39.1%, respectively. State and local health departments, in collaboration with CDC, should continue working to improve reporting of cases and completeness of critical varicella-specific variables to better monitor impact of the varicella vaccination program.