Epidemiology of varicella in Connecticut, 2001-2005

Monitoring Varicella Vaccine Impact on Varicella Incidence in the United States: Surveillance Challenges and Changing Epidemiology, 1995-2019

Surveillance is critical for monitoring vaccine impact. Varicella surveillance challenges predated varicella vaccine US licensure in 1995. Several interim steps were needed before case-based surveillance could be established in most states, and both active and passive surveillance was needed to document the vaccination program's impact on varicella incidence. By the end of the 1-dose program in 2005, incidence had declined 90% in the active surveillance areas, with significant declines occurring in all age groups within 5 years of program implementation. Additional declines occurred during the 2-dose program leading to >97% decline in incidence over the 25 years of program implementation through 2019, based on data from 4 states with continuous passive reporting. Surveillance showed that declines were highest among children and adolescents covered by the routine vaccination recommendations but occurred in all age groups. Although surveillance systems changed and were adapted to reflect evolving epidemiology, data consistently demonstrated decreasing varicella incidence following the vaccination program implementation. The vaccination program dramatically decreased virus circulation and increased community protection. Continued and improved varicella surveillance is needed to accurately monitor disease epidemiology and further guide prevention efforts.

Seroepidemiology of varicella in Hangzhou, China in the vaccine era

Objective To delineate seroepidemiology of VZV in children aged 1-14 years in Hangzhou, to evaluate immunological response of VarV via 2 dose regimen immunization of VarV, for improving immunization strategy of VarV. Methods From 2014-2016, a multi-stage stratified random sampling method was employed to select participants included via physical examination for children in the Community Health Centre in Hangzhou. Results were compared among 11 various age groups: 1-,2-,3-,4-,5-,6-,7-,8-,9-,10-,11-14 years. Demographic data and vaccination history of all subjects derived from Zhejiang Information System for Immunization Program. Then, the second dose of the VarV was conducted on children aged 4-6 years who had immunization history of one dose of VarV. ELISA was used to detect VZV IgG in serum samples. Results 895 subjects with available information were included. The rate of VZV IgG seropositivity was 65.59% and the geometric mean concentration (GMC) for VZV IgG was 5.14 ± 1.89 mIU/ml. The GMC in urban subjects were higher than rural ones. Both the rate of VZV IgG seropositivity and the GMC in children aged 4-6 years groups were statistically lower than participants younger than 4 years and aged 7-14 years (1-,2-,3-,7-,8-,9-,10-,11-14 years). 627 subjects had immunization history of VarV. Both the rate of VZV IgG seropositivity and the GMC in subjects had immunization history of VarV was higher than who had no immunization history.90 subjects were included after the 2nd dose immunization of VarV. Both the rate of VZV IgG seropositivity and the GMC were significantly increased after the immunization of the 2nd dose of VarV. Conclusions The GMC for VZV IgG in children aged 4-6 years were lower than participants groups (1-,2-,3-,7-,8-,9-,10-,11-14 years).2 doses regimen immunization of VarV are effective for increasing both the rate of VZV IgG seropositivity and the GMC in these subjects.

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.

Continuing Decline in Varicella Incidence After the 2-Dose Vaccination Recommendation-Connecticut, 2009-2014

Background. Varicella is a highly contagious vaccine-preventable illness. In 1996, the Advisory Committee for Immunization Practices recommended 1 dose of vaccine for children, and in 2006 it recommended 2 doses; Connecticut required 1 dose for school entry in 2000 and 2 doses for school entry starting in 2011. Connecticut varicella incidence overall and among persons aged 1–14 years declined during 2005–2008. We analyzed varicella surveillance data for 2009–2014 to characterize overall and age group-specific trends in the setting of the 2-dose requirement.

Methods. Passive surveillance was used to collect data and identify incidence trends and changes in proportions, and these were assessed by χ² tests for trend and proportion, respectively.

Results. Varicella incidence decreased from 13.8 cases/100 000 persons during 2009 to 5.1 cases/100 000 persons during 2014 (P < .001); significant declines in incidence occurred among children aged 1–4, 5–9, and 10–14 years (P < .01 for each age group). Cases classified as preventable decreased from 44% during 2009 to 25% during 2014 (P < .01); significant declines in percentages of preventable cases occurred only among those aged 5–9 years (P < .05) and 10–14 (P < .01) years.

Conclusions. Varicella incidence continued to decline in Connecticut in the setting of the 2-dose school-entry program. Continued surveillance is needed to assess the full influence of the 2-dose recommendation.

Trends in hospitalizations with primary varicella and herpes zoster during the prevaricella and initial postvaricella and herpes zoster vaccine eras, connecticut, 1994-2012

Background.  The introductions of the varicella vaccine in 1995 and herpes zoster (HZ) vaccine in 2006 have an ongoing potential to modify the epidemiology of both diseases. Analysis of data on hospitalizations can be conducted to examine trends in the occurrence of severe disease over time and to assess the possible impact of vaccination on the incidence of hospitalization. Methods.  Statewide hospital discharge data 1994-2012 in Connecticut were used to identify individuals discharged with a diagnosis of varicella and the initial admissions of persons with a discharge diagnosis of HZ in the first or second diagnostic position. Trends in overall age-standardized and age group-specific hospitalization rates for preselected time intervals before and after the introduction of vaccines were examined using Poisson regression models or Mantel-Haenszel χ(2) tests. Results.  Beginning in 2001, 5 years after the introduction of varicella vaccine, HZ hospitalization rates decreased significantly in individuals <15 years at an average rate of 19.4% per year through 2012. Among individuals ≥60 years, HZ hospitalization rates increased by 5.1% per year from 2001 to 2006 but decreased by 4.2% per year from 2007 to 2012. Primary varicella hospitalization rates declined 82.9% from the prevaccine era (1994-1995) to the 1-dose era (2001-2005) (P < .001). Rates further decreased significantly in the 2-dose era (2010-2012) among 5 to 9 year olds (100% decrease). Conclusions.  Varicella vaccine seems to have had an impact on both varicella and HZ hospitalizations, and introduction of the HZ vaccine may be having an impact on HZ hospitalizations.

Impact of 2-dose vaccination on varicella epidemiology: Connecticut--2005-2008

In 2006, the Advisory Committee on Immunization Practices recommended that children routinely receive 2 varicella vaccine doses in place of the 1 dose previously recommended. This recommendation's initial impact on varicella epidemiology in Connecticut was assessed. Reported incidence and case-specific data were compared for 2005 and 2008. Varicella incidence decreased from 48.7 cases/100,000 persons in 2005 to 24.5 in 2008. Age-specific incidence decreased significantly (P < .05) among children aged 1-14 years. Reported varicella incidence has declined in Connecticut after implementation of routine 2-dose varicella vaccination for children. Continued surveillance is needed to determine the recommendation's full impact.

Varicella vaccination in Europe - taking the practical approach

Varicella is a common viral disease affecting almost the entire birth cohort. Although usually self-limiting, some cases of varicella can be serious, with 2 to 6% of cases attending a general practice resulting in complications. The hospitalisation rate for varicella in Europe ranges from 1.3 to 4.5 per 100,000 population/year and up to 10.1% of hospitalised patients report permanent or possible permanent sequelae (for example, scarring or ataxia). However, in many countries the epidemiology of varicella remains largely unknown or incomplete. In countries where routine childhood vaccination against varicella has been implemented, it has had a positive effect on disease prevention and control. Furthermore, mathematical models indicate that this intervention strategy may provide economic benefits for the individual and society. Despite this evidence and recommendations for varicella vaccination by official bodies such as the World Health Organization, and scientific experts in the field, the majority of European countries (with the exception of Germany and Greece) have delayed decisions on implementation of routine childhood varicella vaccination, choosing instead to vaccinate high-risk groups or not to vaccinate at all. In this paper, members of the Working Against Varicella in Europe group consider the practicalities of introducing routine childhood varicella vaccination in Europe, discussing the benefits and challenges of different vaccination options (vaccination vs. no vaccination, routine vaccination of infants vs. vaccination of susceptible adolescents or adults, two doses vs. one dose of varicella vaccine, monovalent varicella vaccines vs. tetravalent measles, mumps, rubella and varicella vaccines, as well as the optimal interval between two doses of measles, mumps, rubella and varicella vaccines). Assessment of the epidemiology of varicella in Europe and evidence for the effectiveness of varicella vaccination provides support for routine childhood programmes in Europe. Although European countries are faced with challenges or uncertainties that may have delayed implementation of a childhood vaccination programme, many of these concerns remain hypothetical and with new opportunities offered by combined measles, mumps, rubella and varicella vaccines, reassessment may be timely.