Perspectives on the Impact of Varicella Immunization on Herpes Zoster. A Model-Based Evaluation from Three European Countries

Fundacion Huesped, Argentina
PLoS ONE (Impact Factor: 3.53). 04/2013; 8(4):e60732. DOI: 10.1371/journal.pone.0060732
Source: PubMed

ABSTRACT The introduction of mass vaccination against Varicella-Zoster-Virus (VZV) is being delayed in many European countries because of, among other factors, the possibility of a large increase in Herpes Zoster (HZ) incidence in the first decades after the initiation of vaccination, due to the expected decline of the boosting of Cell Mediated Immunity caused by the reduced varicella circulation. A multi-country model of VZV transmission and reactivation, is used to evaluate the possible impact of varicella vaccination on HZ epidemiology in Italy, Finland and the UK. Despite the large uncertainty surrounding HZ and vaccine-related parameters, surprisingly robust medium-term predictions are provided, indicating that an increase in HZ incidence is likely to occur in countries where the incidence rate is lower in absence of immunization, possibly due to a higher force of boosting (e.g. Finland), whereas increases in HZ incidence might be minor where the force of boosting is milder (e.g. the UK). Moreover, a convergence of HZ post vaccination incidence levels in the examined countries is predicted despite different initial degrees of success of immunization policies. Unlike previous model-based evaluations, our investigation shows that after varicella immunization an increase of HZ incidence is not a certain fact, rather depends on the presence or absence of factors promoting a strong boosting intensity and which might or not be heavily affected by changes in varicella circulation due to mass immunization. These findings might explain the opposed empirical evidences observed about the increases of HZ in sites where mass varicella vaccination is ongoing.

Download full-text


Available from: Giorgio Guzzetta, Jul 06, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: For viral infections conferring what is usually considered as permanent immunity, re-exposure to the pathogen due to contacts with infectious individuals might be critical for immunity boosting. A major example is represented by the varicella-zoster virus (VZV) where re-exposure is thought to lead to boosting of cell mediated immunity (CMI), which plays a protective role against the development of herpes zoster (HZ).Similar concerns have recently been raised also in relation to measles. However, while the first effective exposure, i.e. infection, has been the object of many studies, both theoretical and epidemiological, there has been no corresponding investigation of the re-exposure process. By combining basic concepts from deterministic and stochastic modelling of infection, we develop a basic model for quantifying the timing and number of re-exposures and, consequently, the potential for immune boosting at any given age. The model is then applied to measles, mumps and rubella (MMR) in the UK, and to varicella in Italy, using literature estimates of the pre-vaccination forces of infection. We supply analytical expressions for the expected number of lifetime re-exposures and for underlying age-patterns, including the average age at which the last re-exposure occurs. Based on updated estimates of the force of VZV infection, we show that the expected number of boosting opportunities of CMI might be in the range 2-3, which is consistent with recent findings about the development of herpes zoster. We also show that the estimate of the age at which the last re-exposure to VZV occurs is highly sensitive to the underlying form of age dependence of the force of infection. Our results contribute to the study of the potential immunity boosting effect of re-exposures to an infective agent by quantifying the re-exposure process.
    Mathematical biosciences 07/2013; 245(1). DOI:10.1016/j.mbs.2013.07.013 · 1.49 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Epidemiologic data of Herpes Zoster (HZ) disease in Spain are scarce. The objective of this study was to assess the epidemiology of HZ in the Valencian Community (Spain), using outpatient and hospital electronic health databases. Data from 2007 to 2010 was collected from computerized health databases of a population of around 5 million inhabitants. Diagnoses were recorded by physicians using the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM). A sample of medical records under different criteria was reviewed by a general practitioner, to assess the reliability of codification. The average annual incidence of HZ was 4.60 per 1000 persons-year (PY) for all ages (95% CI: 4.57-4.63), is more frequent in women [5.32/1000PY (95%CI: 5.28-5.37)] and is strongly age-related, with a peak incidence at 70-79 years. A total of 7.16/1000 cases of HZ required hospitalization. Electronic health database used in the Valencian Community is a reliable electronic surveillance tool for HZ disease and will be useful to define trends in disease burden before and after HZ vaccine introduction.
    BMC Infectious Diseases 10/2013; 13(1):463. DOI:10.1186/1471-2334-13-463 · 2.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study aimed to estimate total and age-specific incidence rates of HZ with data from electronic clinical records in primary care (ECRPC) and to analyze trends by sex and age. Descriptive cross-sectional study covering the incident HZ episodes registered in the ECRPC of the Madrid Regional Public Health System in 2005-2012. Annual crude and age-adjusted incidence rates were calculated. Differences by sex and age were assessed by poisson regression. The annual percentage of change (APC) of incidence rates and 'breakthrough points' of the time trends were determined with the Joinpoint Regression Program. 211,650 episodes of HZ were identified (60.6% women, 52.2% > 55 years). The incidence rate increased from 363.21 to 481.92 per 100,000 person-year in 2005-2012. Rates were higher among women and increased with age. The APC for the period was 3.59% in men and 3.67% in women (p<0.05). Age-specific rates increased in patients over 14 years. The APC in the 25-44 age group was 7.4% since 2007. The incidence rate ratio (women/men) was highest in this group. The incidence of HZ presents an upward trend in 2005-2012 in adults and the elderly. Monitoring the incidence and age-specific rates, will help to detect changes in trends.
    The Journal of infection 11/2013; 68(4). DOI:10.1016/j.jinf.2013.09.035 · 4.02 Impact Factor