Analysis of population immunity to poliovirus following cessation of trivalent oral polio vaccine

BACKGROUND

The global withdrawal of trivalent oral poliovirus vaccine (OPV) (tOPV, containing Sabin poliovirus strains serotypes 1, 2 and 3) from routine immunization, and the introduction of bivalent OPV (bOPV, containing Sabin poliovirus strains serotypes 1 and 3) and trivalent inactivated poliovirus vaccine (IPV) into routine immunization was expected to improve population serologic and mucosal immunity to types 1 and 3 poliovirus, while population mucosal immunity to type 2 poliovirus would decline. However, over the period since tOPV withdrawal, the implementation of preventive bOPV supplementary immunization activities (SIAs) has decreased, while outbreaks of type 2 circulating vaccine derived poliovirus (cVDPV2) have required targeted use of monovalent type 2 OPV (mOPV2).

METHODS

We develop a dynamic model of OPV-induced immunity to estimate serotype-specific, district-level immunity for countries in priority regions and characterize changes in immunity since 2016. We account for the changes in routine immunization schedules and varying implementation of preventive and outbreak response SIAs, assuming homogenous coverages of 50% and 80% for SIAs.

RESULTS

In areas with strong routine immunization, the switch from tOPV to bOPV has likely resulted in gains in population immunity to types 1 and 3 poliovirus. However, we estimate that improved immunogenicity of new schedules has not compensated for declines in preventive SIAs in areas with weak routine immunization. For type 2 poliovirus, without tOPV in routine immunization or SIAs, mucosal immunity has declined nearly everywhere, while use of mOPV2 has created highly heterogeneous population immunity for which it is important to take into account when responding to cVDPV2 outbreaks.

CONCLUSIONS

The withdrawal of tOPV and declining allocations of resources for preventive bOPV SIAs have resulted in reduced immunity in vulnerable areas to types 1 and 3 poliovirus and generally reduced immunity to type 2 poliovirus in the regions studied, assuming homogeneous coverages of 50% and 80% for SIAs. The very low mucosal immunity to type 2 poliovirus generates substantially greater risk for further spread of cVDPV2 outbreaks. Emerging gaps in immunity to all serotypes will require judicious targeting of limited resources to the most vulnerable populations by the Global Polio Eradication Initiative (GPEI).

How Does Option Value Affect the Potential Cost-Effectiveness of a Treatment? The Case of Ipilimumab for Metastatic Melanoma

BACKGROUND

Innovations that extend life can generate option value and cost of experiencing future technologies.

OBJECTIVES

To understand how consideration of option value may affect the potential cost-effectiveness of a treatment through a case study of ipilimumab for previously untreated metastatic melanoma.

METHODS

We estimated the cost-effectiveness of ipilimumab in 2 scenarios: a conventional scenario, for which we constructed the model using the standard methods that rely on efficacy data directly from the phase III trial of ipilimumab, and an option value scenario, where we incorporated future hypothetical improvements in mortality for metastatic melanoma owing to innovations. We developed 2 approaches to incorporate option value. In the first approach, we forecasted mortality trends based on historical trends from the Surveillance, Epidemiology, and End Results (SEER) Program registry. Alternatively, we identified drugs being studied in clinical trials at the time of ipilimumab's approval on clinicaltrials.gov and estimated their likelihood and timing of approval, potential efficacy, and cost. We accounted for increases in overall cancer treatment cost and unrelated medical cost in the option value scenario.

RESULTS

In the option value scenario, using the SEER approach, the incremental quality-adjusted life-years (QALYs) gained and the incremental cost increased by 6.2% and 3.8%, respectively, whereas the incremental cost-effectiveness ratio (ICER) decreased by 2.3% compared with the conventional scenario. Using the clinicaltrials.gov approach, the incremental QALY gained and the incremental cost increased by 7.5% and 7.1%, respectively, whereas the ICER decreased by 0.40%.

CONCLUSIONS

We developed generalizable approaches to estimating option value in cost-effectiveness analysis.

Who should be included in a clinical trial of screening for bladder cancer?: a decision analysis of data from the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial

BACKGROUND

Because of its relatively low incidence, bladder cancer screening might have a better ratio of benefits to harms if it is restricted to a high-risk population. Data from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial were used and simple decision analytic techniques were applied to compare different eligibility criteria for a screening trial.

METHODS

For a variety of possible eligibility criteria, the percentage of the population aged 55 years to 74 years and classified as being at high risk for developing invasive or high-grade carcinoma, and therefore likely to benefit from screening, was calculated. Regression models were used to calculate a risk score based on age, sex, smoking history, and family history of bladder cancer. The reduction in cases was calculated given hypothetical risk reductions associated with screening. The trade-off between patients screened and tumors avoided was calculated as a net benefit.

RESULTS

The 5-year probability of being diagnosed with invasive bladder cancer was 0.24%. Using a risk score > 6 or > 8 as the eligibility criterion for a trial was generally superior to including all older adults. In a typical scenario, a risk score > 6 would result in approximately 25% of the population being screened to prevent 57 invasive or high-grade bladder cancers per 100,000 population; screening the entire population would prevent only an additional 38 cases.

CONCLUSIONS

Screening for bladder cancer can be optimized by restricting it to a subgroup of patients considered to be at elevated risk. Different eligibility criteria for a screening trial can be compared rationally using decision-analytic techniques.

Individualized estimation of the benefit of radical prostatectomy from the Scandinavian Prostate Cancer Group randomized trial

BACKGROUND

Although there is randomized evidence that radical prostatectomy improves survival, there are few data on how benefit varies by baseline risk.

OBJECTIVE

We aimed to create a statistical model to calculate the decrease in risk of death associated with surgery for an individual patient, using stage, grade, prostate-specific antigen, and age as predictors.

DESIGN, SETTING, AND PARTICIPANTS

A total of 695 men with T1 or T2 prostate cancer participated in the Scandinavian Prostate Cancer Group 4 trial (SPCG-4).

INTERVENTION

Patients in SPCG-4 were randomized to radical prostatectomy or conservative management.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Competing risk models were created separately for the radical prostatectomy and the watchful waiting group, with the difference between model predictions constituting the estimated benefit for an individual patient.

RESULTS AND LIMITATIONS

Individualized predictions of surgery benefit varied widely depending on age and tumor characteristics. At 65 yr of age, the absolute 10-yr risk reduction in prostate cancer mortality attributable to radical prostatectomy ranged from 4.5% to 17.2% for low- versus high-risk patients. Little expected benefit was associated with surgery much beyond age 70. Only about a quarter of men had an individualized benefit within even 50% of the mean. A limitation is that estimates from SPCG-4 have to be applied cautiously to contemporary patients.

CONCLUSIONS

Our model suggests that it is hard to justify surgery in patients with Gleason 6, T1 disease or in those patients much above 70 yr of age. Conversely, surgery seems unequivocally of benefit for patients who have Gleason 8, or Gleason 7, stage T2. For patients with Gleason 6 T2 and Gleason 7 T1, treatment is more of a judgment call, depending on patient preference and other clinical findings, such as the number of positive biopsy cores and comorbidities.

Against quantiles: categorization of continuous variables in epidemiologic research, and its discontents

Background

Quantiles are a staple of epidemiologic research: in contemporary epidemiologic practice, continuous variables are typically categorized into tertiles, quartiles and quintiles as a means to illustrate the relationship between a continuous exposure and a binary outcome.

Discussion

In this paper we argue that this approach is highly problematic and present several potential alternatives. We also discuss the perceived drawbacks of these newer statistical methods and the possible reasons for their slow adoption by epidemiologists.

Summary

The use of quantiles is often inadequate for epidemiologic research with continuous variables.

Feasibility study of a clinically-integrated randomized trial of modifications to radical prostatectomy

Abstract

Trial registration

ClinicalTrials.gov NCT00928850