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Live attenuated Varicella-Zoster vaccine: Is it worth it?
... The disease outcomes reported were influenza in eight studies [4][5][6][7][8][9][10][11], tuberculosis in four studies [12][13][14][15], as well as three studies each of herpes zoster (HZ) [16][17][18], human papilloma virus (HPV) [19][20][21], and pertussis [22][23][24]. Two studies each focused on Hepatitis A [25,26] and pneumococcal disease [4,27]. ...
... One third of the included studies (n = 9) used data from observational studies, which were primarily cohort studies [8][9][10]12,17,23,27,28,30]. In addition, seven studies were cost-effectiveness and economic analyses [4,5,13,15,16,21,22], six studies were systematic reviews [6,7,11,14,26,29]; three were commentaries [18,20,25], and two studies utilized mathematical modelling [19,24]. Study characteristics of the included studies are summarized in Table 1. ...
... Two studies used NNV to evaluate the potential benefits against HZ. Skootsky described the NNV as an alternate measure of efficacy against HZ [18]. It was reported that one case of HZ was avoided for every 175 adults over 60 years of age who were vaccinated, and one prevented for every 231 adults 70 years of age or older. ...
The number needed to vaccinate (NNV) is a measure that has been widely used in the scientific literature to draw conclusions about the usefulness and cost-effectiveness of various immunization programmes. The main objective of this review is to examine how and why the NNV has been used and reported in the published literature.
Electronic databases were searched and records were screened against the eligibility criteria by two independent authors. We included papers that reported and interpreted NNV.
We identified 27 studies, the designs including observational studies, economic analyses, systematic reviews, and commentaries. The NNV has been used in the literature to describe three main themes: potential benefits of vaccination programmes, cost-effectiveness, and economic analyses, and modelling studies to compare different vaccination strategies.
NNV has been used in a wide variety of ways in the literature, yet there are no defined thresholds for what is a favourable NNV. Furthermore, the generalizability of the NNV is usually limited. Further work is required to determine the most appropriate use of this measure.
Copyright © 2014. Published by Elsevier Ltd.
... Based on the randomized, double-blind, placebo-controlled HZ trial by Oxman et al. which tracked 38,546 healthy subjects aged 60 years and older (median age 69 years) for a mean duration of 3.13 years [152] and using the current cost of about $200 per dose (based on the Rite Aid ® or Walgreens pharmacy fee), the costs per year to prevent one case of HZ and one case of PHN were, respectively: $35,000 (where number needed to vaccinate, NNV = 175) and $217,400 (where NNV = 1087) [153]. ...
Varicella vaccination is generally considered safe but there are usually no prescreening tests to determine whether an adverse reaction is likely to occur. The literature contains a surprising number of adverse reactions following varicella vaccination including vaccine-strain herpes-zoster (HZ) in children and adults. The Advisory Committee on Immunization Practices (ACIP) states, "VAERS data are limited by underreporting and unknown sensitivity of the reporting system, making it difficult to compare adverse event rates following vaccination reported to VAERS with those from complications following natural disease. Nevertheless, the magnitude of these differences makes it likely that serious adverse events following vacci-nation occur at a substantially lower rate than following natural disease." Since follow-up is not conducted, it may be argued that some reports may not be attributed to or associated with vaccination and therefore the true rate of adverse events is essentially unknown. Nevertheless, adverse reac-tions reported in VAERS have typically been shown to be only 5% or 10% of the true rates. Cost-benefit analyses of the universal varicella vaccina-tion program appear to be optimistic, especially when adverse vaccine reactions are completely ignored or excluded.
... Based on the randomized, double-blind, placebo-controlled HZ trial by Oxman et al. which tracked 38,546 healthy subjects aged 60 years and older (median age 69 years) for a mean duration of 3.13 years [152] and using the current cost of about $200 per dose (based on the Rite Aid ® or Walgreens pharmacy fee), the costs per year to prevent one case of HZ and one case of PHN were, respectively: $35,000 (where number needed to vaccinate, NNV = 175) and $217,400 (where NNV = 1087) [153]. ...
In a cooperative agreement starting January 1995, prior to the FDA's licensure of the varicella vaccine on March 17, the Centers for Disease Control and Prevention (CDC) funded the Los Angeles Department of Health Services' Antelope Valley Varicella Active Surveillance Project (AV-VASP). Since only varicella case reports were gathered, baseline incidence data for herpes zoster (HZ) or shingles was lacking. Varicella case reports decreased 72%, from 2834 in 1995 to 836 in 2000 at which time approximately 50% of children under 10years of age had been vaccinated. Starting in 2000, HZ surveillance was added to the project. By 2002, notable increases in HZ incidence rates were reported among both children and adults with a prior history of natural varicella. However, CDC authorities still claimed that no increase in HZ had occurred in any US surveillance site. The basic assumptions inherent to the varicella cost-benefit analysis ignored the significance of exogenous boosting caused by those shedding wild-type VZV. Also ignored was the morbidity associated with even rare serious events following varicella vaccination as well as the morbidity from increasing cases of HZ among adults. Vaccine efficacy declined below 80% in 2001. By 2006, because 20% of vaccinees were experiencing breakthrough varicella and vaccine-induced protection was waning, the CDC recommended a booster dose for children and, in 2007, a shingles vaccination was approved for adults aged 60years and older. In the prelicensure era, 95% of adults experienced natural chickenpox (usually as children)-these cases were usually benign and resulted in long-term immunity. Varicella vaccination is less effective than the natural immunity that existed in prevaccine communities. Universal varicella vaccination has not proven to be cost-effective as increased HZ morbidity has disproportionately offset cost savings associated with reductions in varicella disease. Universal varicella vaccination has failed to provide long-term protection from VZV disease.
... 6 The number needed to vaccinate (NNV), an analogous measure to the number needed to treat (NNT), 7 can be very helpful to illustrate the potential benefit of herpes zoster vaccination as it combines both the effect of vaccine efficacy and the age-specific background incidence of disease. Although a previous study, by Skootsky,8 has estimated the NNV to prevent a case of herpes zoster and a case of PHN, NNV for other herpes zoster health outcomes such as mortality and hospitalization have yet to be assessed. Furthermore, by estimating NNV directly from the Shingles Prevention Study, 6 Skootksy 8 did not incorporate uncertainties around the potential medium-to long-term decline in vaccine protection (maximum followup time in the clinical trial was 5 years (mean = 3.13 years)). ...
A clinical trial has shown that a live-attenuated varicella-zoster virus vaccine is effective against herpes zoster (HZ) and post-herpetic neuralgia (PHN). The aim of the study was to estimate the number needed to vaccinate (NNV) to prevent HZ-related outcomes.
A cohort model of HZ associated disease, health care resource use and mortality was developed. Canadian population-based data were used to estimate age-specific incidence, hospitalization, quality-adjusted life-year (QALY) lost and mortality. NNV was calculated as the number of individuals needed to be vaccinated to prevent a specific HZ-related outcome during their lifetime. Different ages at vaccination were examined and probabilistic sensitivity analysis was performed.
For 65 year olds, the NNV (HZ vaccine efficacy=63%, PHN vaccine efficacy=67%, no waning) to prevent a case of HZ, a case of PHN, a HZ death, a life-year lost and a QALY lost is estimated to be 11 (90% Crl: 10-13), 43 (90% Crl: 33-53), 23,319 (90% Crl: 15,312-33,139), 3762 (90% Crl: 1650-4629) and 165 (90% Crl: 105-197), respectively. Results were most sensitive to the duration of vaccine protection and the age at vaccination.
The predicted NNV to prevent HZ and PHN are low even though vaccine efficacy is between 50-70%, which reflects the high incidence of these diseases among older adults. Results clearly show that the main benefit of HZ vaccination is prevention of morbidity caused by pain (as measured by QALYs lost) rather than mortality.
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