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

Mahamud, Abdirahman; Wiseman, Rachel; Grytdal, Scott; Basham, Candyce; Asghar, Jawaid; Dang, Thi; Leung, Jessica; Lopez, Adriana; Schmid, Daniela; Bialek, Stephanie R.

doi:10.1016/j.vaccine.2012.07.076

Cited by 27 publications

(15 citation statements)

References 21 publications

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“…There were 2 large outbreaks with ≥51 cases reported in 2010–2012. One outbreak has been previously described 14 , involved 2 elementary schools and 60 vaccinated cases with 48% 1-dose cases and 52% 2-dose cases. The other large outbreak occurred in a K-8 th grade school and involved 55 cases; information on vaccination status was available for 13% of cases, all of whom were vaccinated with 1-dose.…”

Section: Resultsmentioning

confidence: 99%

Impact of the US Two-dose Varicella Vaccination Program on the Epidemiology of Varicella Outbreaks

Leung

Lopez

Blostein

et al. 2015

Pediatric Infectious Disease Journal

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Background A routine 2-dose varicella vaccination program was adopted in 2007 in the United States to help further decrease varicella disease and prevent varicella outbreaks. We describe trends and characteristics of varicella outbreaks reported to CDC during 2005–2012 from 9 states. Methods Data on varicella outbreaks collected by 9 state health departments were submitted to CDC using the CDC outbreak reporting worksheet. Information was collected on dates of the outbreak, outbreak setting, and number of cases by outbreak; aggregate data was provided on the numbers of outbreak-related cases by age group, vaccination status, and laboratory confirmation. Results Nine hundred and twenty-nine outbreaks were reported from the 6 states which provided data for each year during 2005–2012. Based on data from these 6 states, the number of outbreaks declined by 78%, decreasing from 147 in 2005 to 33 outbreaks in 2012 (p=0.0001). There were a total of 1,015 varicella outbreaks involving 13,595 cases reported by the 9 states from 2005–2012. The size and duration of outbreaks declined significantly over time (p<0.001). The median size of outbreaks was 12, 9, and 7 cases and median duration of outbreaks was 38, 35, and 26 days during 2005–2006, 2007–2009, and 2010–2012 respectively. Majority of outbreaks (95%) were reported from schools, declining from 97% in 2005–2006 to 89% in 2010–2012. Sixty-five percent of outbreak-related cases occurred among 5–9 year olds, with the proportion declining from 76% in 2005–2006 to 45% during 2010–2012. Conclusions The routine 2-dose varicella vaccination program appears to have significantly reduced the number, size, and duration of varicella outbreaks in the U.S.

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Section: Resultsmentioning

confidence: 99%

Impact of the US Two-dose Varicella Vaccination Program on the Epidemiology of Varicella Outbreaks

Leung

Lopez

Blostein

et al. 2015

Pediatric Infectious Disease Journal

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“…Although none of the outbreak-related cases identified in AV had received 2 doses of varicella vaccine, large outbreaks involving 2-dose vaccinees have been reported. 26 Investigating cases and outbreaks among 1- and 2-dose vaccinees who present with modified disease is challenging in that it can be difficult to distinguish mild breakthrough varicella from other causes of rash and collect adequate specimens from maculopapular lesions for laboratory testing. 26 As the positive predictive value of clinical diagnosis declines, better laboratory tools, including alternative specimen types suitable for collection in outbreak investigations that commence after rash resolution, are needed.…”

Section: Discussionmentioning

confidence: 99%

“…26 Investigating cases and outbreaks among 1- and 2-dose vaccinees who present with modified disease is challenging in that it can be difficult to distinguish mild breakthrough varicella from other causes of rash and collect adequate specimens from maculopapular lesions for laboratory testing. 26 As the positive predictive value of clinical diagnosis declines, better laboratory tools, including alternative specimen types suitable for collection in outbreak investigations that commence after rash resolution, are needed. 27 Going forward, clinician education on the growing importance of laboratory confirmation of varicella will be important to ensure appropriate implementation of varicella control strategies.…”

Section: Discussionmentioning

confidence: 99%

Impact of a Routine Two-Dose Varicella Vaccination Program on Varicella Epidemiology

et al. 2013

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OBJECTIVE One-dose varicella vaccination for children was introduced in the United States in 1995. In 2006, a second dose was recommended to further decrease varicella disease and outbreaks. We describe the impact of the 2-dose vaccination program on varicella incidence, severity, and outbreaks in 2 varicella active surveillance areas. METHODS We examined varicella incidence rates and disease characteristics in Antelope Valley (AV), CA, and West Philadelphia, PA, and varicella outbreak characteristics in AV during 1995–2010. RESULTS In 2010, varicella incidence was 0.3 cases per 1000 population in AV and 0.1 cases per 1000 population in West Philadelphia: 76% and 67% declines, respectively, since 2006 and 98% declines in both sites since 1995; incidence declined in all age groups during 2006–2010. From 2006–2010, 61.7% of case patients in both surveillance areas had been vaccinated with 1 dose of varicella vaccine and 7.5% with 2 doses. Most vaccinated case patients had <50 lesions with no statistically significant differences among 1- and 2-dose cases (62.8% and 70.3%, respectively). Varicella-related hospitalizations during 2006–2010 declined >40% compared with 2002–2005 and >85% compared with 1995–1998. Twelve varicella outbreaks occurred in AV during 2007–2010, compared with 47 during 2003–2006 and 236 during 1995–1998 (P < .01). CONCLUSIONS Varicella incidence, hospitalizations, and outbreaks in 2 active surveillance areas declined substantially during the first 5 years of the 2-dose varicella vaccination program. Declines in incidence across all ages, including infants who are not eligible for varicella vaccination, and adults, in whom vaccination levels are low, provide evidence of the benefit of high levels of immunity in the population.

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“…However, 2 of the estimates, both from outbreak investigations, were <90% and that may have lowered the pooled estimate to the lower 90s. 32,33 The pooled VE estimates we report for 1 dose are a compilation of VE at different points of time since vaccination, primarily within the first decade. Considering the age of participants in the studies and vaccine recommendations in each country, the median time since vaccination is likely lower than 10 years.…”

Section: Figurementioning

confidence: 99%

Global Varicella Vaccine Effectiveness: A Meta-analysis

et al. 2016

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CONTEXT: Several varicella vaccines are available worldwide. Countries with a varicella vaccination program use 1-or 2-dose schedules. OBJECTIVE:We examined postlicensure estimates of varicella vaccine effectiveness (VE) among healthy children.DATA SOURCES: Systematic review and descriptive and meta-analysis of Medline, Embase, Cochrane libraries, and CINAHL databases for reports published during 1995-2014. STUDY SELECTION:Publications that reported original data on dose-specific varicella VE among immunocompetent children. DATA EXTRACTION:We used random effects meta-analysis models to obtain pooled one dose VE estimates by disease severity (all varicella and moderate/severe varicella). Within each severity category, we assessed pooled VE by vaccine and by study design. We used descriptive statistics to summarize 1-dose VE against severe disease. For 2-dose VE, we calculated pooled estimates against all varicella and by study design. RESULTS:The pooled 1-dose VE was 81% (95% confidence interval [CI]: 78%-84%) against all varicella and 98% (95% CI: 97%-99%) against moderate/severe varicella with no significant association between VE and vaccine type or study design (P > .1). For 1 dose, median VE for prevention of severe disease was 100% (mean = 99.4%). The pooled 2-dose VE against all varicella was 92% (95% CI: 88%-95%), with similar estimates by study design.LIMITATIONS: VE was assessed primarily during outbreak investigations and using clinically diagnosed varicella. CONCLUSIONS:One dose of varicella vaccine was moderately effective in preventing all varicella and highly effective in preventing moderate/severe varicella, with no differences by vaccine. The second dose adds improved protection against all varicella.a National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia; and b Department of Immunization, Vaccines and Biologicals, World Health Organization, Geneva, Switzerland Dr Marin conceptualized and designed the study, reviewed the articles and collected the data, supervised the analysis, interpreted the data, drafted the initial manuscript, and revised the manuscript; Dr Marti conceptualized the study, reviewed part of the articles, interpreted the data, and reviewed and revised the manuscript; Ms Kambhampati carried out the meta-analyses, interpreted the data, and reviewed the manuscript; Dr Jeram conducted an initial literature review, reviewed part of the articles and collected the data, and reviewed the manuscript; Dr Seward conceptualized and designed the study, reviewed part of the articles, critically reviewed the manuscript, and interpreted the data; and all authors approved the fi nal manuscript as submitted.The fi ndings and conclusions in this report are those of the authors and do not necessarily represent the offi cial position of the Centers for Disease Control and Prevention. For authors affi liated with the World Health Organization, the authors alone are responsible for the views expressed in this publication ...

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

Cited by 27 publications

References 21 publications

Impact of the US Two-dose Varicella Vaccination Program on the Epidemiology of Varicella Outbreaks

Impact of the US Two-dose Varicella Vaccination Program on the Epidemiology of Varicella Outbreaks

Impact of a Routine Two-Dose Varicella Vaccination Program on Varicella Epidemiology

Global Varicella Vaccine Effectiveness: A Meta-analysis

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